title: Grizzly bear

text: Although variable in color from blond to nearly black, grizzly bear fur is typically brown with darker legs and commonly white or blond tipped fur on the flank and back.


title: Grizzly bear

text: In North America, grizzly bears previously ranged from Alaska down to Mexico and as far east as the western shores of Hudson Bay; the species is now found in Alaska, south through much of western Canada, and into portions of the northwestern United States (including Washington, Idaho, Montana and Wyoming), extending as far south as Yellowstone and Grand Teton National Parks. In Canada, there are approximately 25,000 grizzly bears occupying British Columbia, Alberta, the Yukon, the Northwest Territories, Nunavut, and the northern part of Manitoba.


title: Grizzly bear

text: An article published in 1954 suggested they may be present in the tundra areas of the Ungava Peninsula and the northern tip of Labrador-Quebec. In British Columbia, grizzly bears inhabit approximately 90% of their original territory. There were approximately 25,000 grizzly bears in British Columbia when the European settlers arrived. However, population size has since significantly decreased due to hunting and habitat loss. In 2008, it was estimated there were 16,000 grizzly bears. A revised Grizzly bear count in 2012 for British Columbia was 15,075. Population estimates for British Columbia are based on hair-snagging, DNA-based inventories, mark-and-recapture, and a refined multiple regression model. In 2003, researchers from the University of Alberta spotted a grizzly on Melville Island in the high Arctic, which is the most northerly sighting ever documented.


title: Grizzly bear

text: Around 60,000 wild grizzly bears are located throughout North America, 30,000 of which are found in Alaska. and up to 29,000 live in Canada. The Alaskan population of 30,000 individuals is the highest population of any province / state in North America. Populations in Alaska are densest along the coast, where food supplies such as salmon are more abundant. The Admiralty Island National Monument protects the densest population: 1,600 bears on a 1,600 square-mile island.The majority of Canada's grizzlies live in British Columbia.


title: Grizzly bear

text: In the lower 48 United States, around 1,000 are found in the Northern Continental Divide in northwestern Montana. About 1,000 more live in the Greater Yellowstone Ecosystem in the tri-state area of Wyoming, Idaho and Montana. There are an estimated 70–100 grizzly bears living in northern and eastern Idaho. In September 2007, a hunter produced evidence of one bear in the Selway-Bitterroot Wilderness ecosystem, by killing a male grizzly bear there.


title: Grizzly bear

text: In the North Cascades ecosystem of northern Washington, grizzly bear populations are estimated to be fewer than 20 bears, but there is a longterm management plan to reintroduce the bears to North Cascades National Park.


title: Grizzly bear

text: The grizzly bear's original range included much of the Great Plains and the southwestern states, but it has been extirpated in most of those areas. Combining Canada and the United States, grizzly bears inhabit approximately half the area of their historical range.


title: Grizzly bear

text: Although the once-abundant California grizzly bear appears prominently on the state flag of California and was the symbol of the Bear Flag Republic before the state of California's admission to the Union in 1850, the subspecies or population is currently extinct. The last known grizzlies in California were killed in the Sierra foothills east of Fresno in the early 1920s.


title: Grizzly bear

text: The killing of the last grizzly bear in Arizona in 1936 at Escudilla Mountain is included in Aldo Leopold's Sand County Almanac. There has been no confirmed sighting of a grizzly in Colorado since 1979.


title: Grizzly bear

text: Other provinces and the United States may use a combination of methods for population estimates. Therefore, it is difficult to say precisely what methods were used to produce total population estimates for Canada and North America, as they were likely developed from a variety of studies. The grizzly bear currently has legal protection in Mexico, European countries, some areas of Canada, and in all of the United States. However, it is expected that repopulating its former range will be a slow process, due to various reasons, including the bear's slow reproductive habits and the effects of reintroducing such a large animal to areas prized for agriculture and livestock.


title: Grizzly bear

text: Grizzly bears hibernate for five to seven months each year (except where the climate is warm—the California grizzly did not hibernate). During this time, female grizzly bears give birth to their offspring, who then consume milk from their mother and gain strength for the remainder of the hibernation period. To prepare for hibernation, grizzlies must prepare a den and consume an immense amount of food because they do not eat during hibernation. Grizzly bears also do not defecate or urinate throughout the entire hibernation period. The male grizzly bear's hibernation ends in early to mid-March, while females emerge in April or early May.


title: Grizzly bear

text: In preparation for winter, bears can gain approximately , during a period of hyperphagia, before going into hibernation. The bear often waits for a substantial snowstorm before it enters its den: such behavior lessens the chances that predators will find the den. The dens are typically at elevations above on north-facing slopes. There is some debate among professionals as to whether grizzly bears technically hibernate: much of this debate revolves around body temperature and the ability of the bears to move around during hibernation on occasion. Grizzly bears can "partially" recycle their body wastes during this period. Although inland or Rocky Mountain grizzlies spend nearly half of their life in dens, coastal grizzlies with better access to food sources spend less time in dens. In some areas where food is very plentiful year round, grizzly bears skip hibernation altogether.


title: Grizzly bear

text: Except for females with cubs, grizzlies are normally solitary, active animals, but in coastal areas, grizzlies gather around streams, lakes, rivers, and ponds during the salmon spawn. Females (sows) produce one to four young (usually two) that are small and weigh only about at birth. A sow is protective of her offspring and will attack if she thinks she or her cubs are threatened.


title: Grizzly bear

text: Grizzly bears have one of the lowest reproductive rates of all terrestrial mammals in North America. This is due to numerous ecological factors. Grizzly bears do not reach sexual maturity until they are at least five years old. Once mated with a male in the summer, the female delays embryo implantation until hibernation, during which miscarriage can occur if the female does not receive the proper nutrients and caloric intake. On average, females produce two cubs in a litter and the mother cares for the cubs for up to two years, during which the mother will not mate.


title: Grizzly bear

text: Once the young leave or are killed, females may not produce another litter for three or more years, depending on environmental conditions. Male grizzly bears have large territories, up to , making finding a female scent difficult in such low population densities. Population fragmentation of grizzlies may destabilize the population from inbreeding depression. The gestation period for grizzly bears is approximately 180–250 days.


title: Grizzly bear

text: Litter size varies between one and four cubs, typically comprising twins or triplets. Cubs are always born in the mother's winter den while she is in hibernation. Female grizzlies are fiercely protective of their cubs, being able to fend off predators including larger male bears. Cubs feed entirely on their mother's milk until summer comes, after which they still drink milk but begin to eat solid foods. Cubs gain weight rapidly during their time with the mother—their weight will have increased from in the two years spent with the mother. Mothers may see their cubs in later years but both avoid each other.


title: Grizzly bear

text: The average lifespan for a male is estimated at 22 years, with that of a female being slightly longer at 26. Females live longer than males due to their less dangerous life; they do not engage in seasonal breeding fights as males do. The oldest known wild inland grizzly was about 34 years old in Alaska; the oldest known coastal bear was 39, but most grizzlies die in their first year of life. Captive grizzlies have lived as long as 44 years.


title: Grizzly bear

text: They have a tendency to chase fleeing animals, and although it has been said anecdotally that grizzly bears ("Ursus arctos horribilis") can run at , the maximum speed reliably recorded at Yellowstone is . In addition, they can climb trees.


title: Grizzly bear

text: Although grizzlies are of the order Carnivora and have the digestive system of carnivores, they are normally omnivores: their diets consist of both plants and animals. They have been known to prey on large mammals, when available, such as moose, elk, caribou, white-tailed deer, mule deer, bighorn sheep, bison, and even black bears, though they are more likely to take calves and injured individuals rather than healthy adults. Grizzly bears feed on fish such as salmon, trout, and bass, and those with access to a more protein-enriched diet in coastal areas potentially grow larger than inland individuals. Grizzly bears also readily scavenge food or carrion left behind by other animals. Grizzly bears will also eat birds and their eggs, and gather in large numbers at fishing sites to feed on spawning salmon. They frequently prey on baby deer left in the grass, and occasionally they raid the nests of raptors such as bald eagles.


title: Grizzly bear

text: Coastal Canadian and Alaskan grizzlies are larger than those that reside in the Rocky Mountains. This is due, in part, to the richness of their diets. In Yellowstone National Park in the United States, the grizzly bear's diet consists mostly of whitebark pine nuts, tubers, grasses, various rodents, army cutworm moths, and scavenged carcasses. None of these, however, match the fat content of the salmon available in Alaska and British Columbia. With the high fat content of salmon, it is not uncommon to encounter grizzlies in Alaska weighing . Grizzlies in Alaska supplement their diet of salmon and clams with sedge grass and berries. In areas where salmon are forced to leap waterfalls, grizzlies gather at the base of the falls to feed on and catch the fish. Salmon are at a disadvantage when they leap waterfalls because they cluster together at their bases and are therefore easier targets for the grizzlies. Grizzly bears are well-documented catching leaping salmon in their mouths at Brooks Falls in Katmai National Park and Preserve in Alaska. They are also very experienced in chasing the fish around and pinning them with their claws. At such sites such as Brooks Falls and McNeil Falls in Alaska, big male grizzlies fight regularly for the best fishing spots. Grizzly bears along the coast also forage for razor clams, and frequently dig into the sand to seek them. During the spring and fall, directly before and after the salmon runs, berries and grass make up the mainstay of the diets of coastal grizzlies.


title: Grizzly bear

text: Inland grizzlies may eat fish too, most notably in Yellowstone grizzlies eating Yellowstone cutthroat trout. The relationship with cutthroat trout and grizzlies is unique because it is the only example where Rocky Mountain grizzlies feed on spawning salmonid fish. However, grizzly bears themselves and invasive lake trout threaten the survival of the trout population and there is a slight chance that the trout will be eliminated.


title: Grizzly bear

text: Grizzly bears occasionally prey on small mammals, such as marmots, ground squirrels, lemmings, and voles. The most famous example of such predation is in Denali National Park and Preserve, where grizzlies chase, pounce on, and dig up Arctic ground squirrels to eat. In some areas, grizzly bears prey on hoary marmots, overturning rocks to reach them, and in some cases preying on them when they are in hibernation. Larger prey includes bison and moose, which are sometimes taken by bears in Yellowstone National Park. Because bison and moose are dangerous prey, grizzlies usually use cover to stalk them and/or pick off weak individuals or calves. Grizzlies in Alaska also regularly prey on moose calves, which in Denali National Park may be their main source of meat. In fact, grizzly bears are such important predators of moose and elk calves in Alaska and Yellowstone that they may kill as many as 51 percent of elk or moose calves born that year. Grizzly bears have also been blamed in the decline of elk in Yellowstone National Park when the actual predators were thought to be gray wolves. In northern Alaska, grizzlies are a significant predator of caribou, mostly taking sick or old individuals or calves. Several studies show that grizzly bears may follow the caribou herds year-round in order to maintain their food supply. In northern Alaska, grizzly bears often encounter muskox. Despite the fact that muskox do not usually occur in grizzly habitat and that they are bigger and more powerful than caribou, predation on muskox by grizzlies has been recorded.


title: Grizzly bear

text: Grizzlies along the Alaskan coast also scavenge on dead or washed up whales. Usually such incidents involve only one or two grizzlies at a carcass, but up to ten large males have been seen at a time eating a dead humpback whale. Dead seals and sea lions are also consumed.


title: Grizzly bear

text: Although the diets of grizzly bears vary extensively based on seasonal and regional changes, plants make up a large portion of them, with some estimates as high as 80–90%. Various berries constitute an important food source when they are available. These can include blueberries, blackberries ("Rubus fruticosus"), salmon berries ("Rubus spectabilis"), cranberries ("Vaccinium oxycoccos"), buffalo berries ("Shepherdia argentea"), soapberries ("Shepherdia canadensis"), and huckleberries ("Vaccinium parvifolium"), depending on the environment. Insects such as ladybugs, ants, and bees are eaten if they are available in large quantities. In Yellowstone National Park, grizzly bears may obtain half of their yearly caloric needs by feeding on miller moths that congregate on mountain slopes. When food is abundant, grizzly bears will feed in groups. For example, many grizzly bears will visit meadows right after an avalanche or glacier slide. This is due to an influx of legumes, such as "Hedysarum", which the grizzlies consume in massive amounts. When food sources become scarcer, however, they separate once again.


title: Grizzly bear

text: The relationship between grizzly bears and other predators is mostly one-sided; grizzly bears will approach feeding predators to steal their kill. In general, the other species will leave the carcasses for the bear to avoid competition or predation. Any parts of the carcass left uneaten are scavenged by smaller animals.


title: Grizzly bear

text: With the reintroduction of gray wolves to Yellowstone, many visitors have witnessed a once common struggle between a keystone species, the grizzly bear, and its historic rival, the gray wolf. The interactions of grizzly bears with the wolves of Yellowstone have been under considerable study. Typically, the conflict will be in the defence of young or over a carcass, which is commonly an elk killed by wolves.


title: Grizzly bear

text: The grizzly bear uses its keen sense of smell to locate the kill. As the wolves and grizzly compete for the kill, one wolf may try to distract the bear while the others feed. The bear then may retaliate by chasing the wolves. If the wolves become aggressive with the bear, it is normally in the form of quick nips at its hind legs. Thus, the bear will sit down and use its ability to protect itself in a full circle. Rarely do interactions such as these end in death or serious injury to either animal. One carcass simply is not usually worth the risk to the wolves (if the bear has the upper hand due to strength and size) or to the bear (if the wolves are too numerous or persistent).


title: Grizzly bear

text: While wolves usually dominate grizzly bears during interactions at wolf dens, both grizzly and black bears have been reported killing wolves and their cubs at wolf dens even when the wolves were acting in defence.


title: Grizzly bear

text: Cougars generally give the bears a wide berth. Grizzlies have less competition with cougars than with other predators, such as coyotes, wolves, and other bears. When a grizzly descends on a cougar feeding on its kill, the cougar usually gives way to the bear. When a cougar does stand its ground, it will use its superior agility and its claws to harass the bear, yet stay out of its reach until one of them gives up. Grizzly bears occasionally kill cougars in disputes over kills. There have been several anecdotes, primarily from the late 19th and early 20th centuries, of cougars and grizzly bears killing each other in fights to the death.


title: Grizzly bear

text: The other big cat present in the United States which might pose a threat to bears is the jaguar; however, both species have been extirpated in the regions of the Southwest where their former habitats overlapped, and grizzlies remain so far absent from the regions along the U.S.-Mexico border, where jaguars appear to be returning.


title: Grizzly bear

text: Black bears generally stay out of grizzly territory, but grizzlies may occasionally enter black bear terrain to obtain food sources both bears enjoy, such as pine nuts, acorns, mushrooms, and berries. When a black bear sees a grizzly coming, it either turns tail and runs or climbs a tree.


title: Grizzly bear

text: Black bears are not strong competition for prey because they have a more herbivorous diet. Confrontations are rare because of the differences in size, habitats, and diets of the bear species. When this happens, it is usually with the grizzly being the aggressor. The black bear will only fight when it is a smaller grizzly such as a yearling or when the black bear has no other choice but to defend itself. There is at least one confirmed observation of a grizzly bear digging out, killing, and eating a black bear when the latter was in hibernation.


title: Grizzly bear

text: The segregation of black bear and grizzly bear populations is possibly due to competitive exclusion. In certain areas, grizzly bears outcompete black bears for the same resources. For example, many Pacific coastal islands off British Columbia and Alaska support either the black bear or the grizzly, but rarely both.


title: Grizzly bear

text: In regions where both species coexist, they are divided by landscape gradients such as the age of forest, elevation, and land openness. Grizzly bears tend to favor old forests with high productivity, higher elevations and more open habitats compared with black bears. However, a bear shot in autumn 1986 in Michigan was thought by some to be a grizzly×black bear hybrid, due to its unusually large size and its proportionately larger braincase and skull, but DNA testing was unable to determine whether it was a large American black bear or a grizzly bear.


title: Grizzly bear

text: Coyotes, foxes, and wolverines are generally regarded merely as pests to grizzlies rather than competition, though they may compete for smaller prey, such as ground squirrels and rabbits. All three will try to scavenge whatever they can from the bears. Wolverines are aggressive enough to occasionally persist until the bear finishes eating, leaving more scraps than normal for the smaller animal. Packs of coyotes have also displaced grizzly bears in disputes over kills.


title: Grizzly bear

text: The removal of wolves and grizzlies in California may have greatly reduced the abundance of the endangered San Joaquin Kit Fox.


title: Grizzly bear

text: The grizzly bear has several relationships with its ecosystem. One such relationship is a mutualistic relationship with fleshy-fruit bearing plants. After the grizzly consumes the fruit, the seeds are excreted and thereby dispersed in a germinable condition. Some studies have shown germination success is indeed increased as a result of seeds being deposited along with nutrients in feces. This makes grizzly bears important seed distributors in their habitats.


title: Grizzly bear

text: While foraging for tree roots, plant bulbs, or ground squirrels, bears stir up the soil. This process not only helps grizzlies access their food, but also increases species richness in alpine ecosystems. An area that contains both bear digs and undisturbed land has greater plant diversity than an area that contains just undisturbed land. Along with increasing species richness, soil disturbance causes nitrogen to be dug up from lower soil layers, and makes nitrogen more readily available in the environment. An area that has been dug by the grizzly bear has significantly more nitrogen than an undisturbed area.


title: Grizzly bear

text: Nitrogen cycling is not only facilitated by grizzlies digging for food, it is also accomplished via their habit of carrying salmon carcasses into surrounding forests. It has been found that spruce tree ("Picea glauca") foliage within of the stream where the salmon have been obtained contains nitrogen originating from salmon on which the bears preyed. These nitrogen influxes to the forest are directly related to the presence of grizzly bears and salmon.


title: Grizzly bear

text: Grizzlies directly regulate prey populations and also help prevent overgrazing in forests by controlling the populations of other species in the food chain. An experiment in Grand Teton National Park in Wyoming in the United States showed removal of wolves and grizzly bears caused populations of their herbivorous prey to increase. This, in turn, changed the structure and density of plants in the area, which decreased the population sizes of migratory birds. This provides evidence grizzly bears represent a keystone predator, having a major influence on the entire ecosystem they inhabit.


title: Grizzly bear

text: When grizzly bears fish for salmon along the coasts of Alaska and British Columbia, they often only eat the skin, brain and roe of the fish. In doing so, they provide a food source for gulls, ravens, and foxes, all of which eat salmon as well; this benefits both the bear and the smaller predators.


title: Grizzly bear

text: Native American tribes living among brown bears often view them with a mixture of awe and fear. North American brown bears have at times been so feared by the Natives that they were rarely hunted by them, especially when alone. At traditional grizzly hunts in some western tribes such as the Gwichʼin, the expedition was conducted with the same preparation and ceremoniality as intertribal warfare and was never done except with a company of four to ten warriors. The tribe members who dealt the killing blow were highly esteemed among their compatriots. Californian Natives actively avoided prime bear habitat and would not allow their young men to hunt alone for fear of bear attacks. During the Spanish colonial period, some tribes would seek aid from European colonists to deal with problem bears instead of hunting grizzlies themselves. Many authors in the American West wrote of Natives or voyageurs with lacerated faces and missing noses or eyes, due to attacks from grizzlies.


title: Grizzly bear

text: Many Native American tribes both respect and fear the brown bear. In Kwakiutl mythology, American black and brown bears became enemies when Grizzly Bear Woman killed Black Bear Woman for being lazy. Black Bear Woman's children, in turn, killed Grizzly Bear Woman's own cubs. Sleeping Bear Dunes is named after an Ojibwe legend, where a female bear and her cubs swam across Lake Michigan. According to the legend, the two cubs drowned and became the Manitou islands. The mother bear eventually got to shore and slept, waiting patiently for her cubs to arrive. Over the years, the sand covered the mother bear up, creating a huge sand dune.


title: Grizzly bear

text: Grizzlies are considered more aggressive compared to black bears when defending themselves and their offspring. Unlike the smaller black bears, adult grizzlies do not climb trees well, and respond to danger by standing their ground and warding off their attackers. Mothers defending cubs are the most prone to attacking, and are responsible for 70% of humans killed by grizzlies.


title: Grizzly bear

text: Grizzly bears normally avoid contact with people. In spite of their obvious physical advantage they rarely actively hunt humans. Most grizzly bear attacks result from a bear that has been surprised at very close range, especially if it has a supply of food to protect, or female grizzlies protecting their offspring.


title: Grizzly bear

text: Increased human–bear interaction has created "problem bears": bears adapted to human activities or habitat. Exacerbating this is the fact that intensive human use of grizzly habitat coincides with the seasonal movement of grizzly bears. Aversive conditioning using rubber bullets, foul-tasting chemicals, or acoustic deterrent devices attempt to condition bears to associate humans with unpleasantness, but is ineffective when the bears have already learned to positively associate humans with food. Such bears are translocated or killed because they pose a threat to humans. The B.C. government kills approximately 50 problem bears each year and overall spends more than one million dollars annually to address bear complaints, relocate bears or kill them. A bear killing a human in a national park may be killed to prevent its attacking again.


title: Grizzly bear

text: Bear awareness programs have been developed by communities in grizzly bear territory to help prevent conflicts with both black and grizzly bears. The main premise of these programs is to teach humans to manage foods that attract bears. Keeping garbage securely stored, harvesting fruit when ripe, securing livestock behind electric fences, and storing pet food indoors are all measures promoted by bear awareness programs. Revelstoke, British Columbia, is a community that demonstrates the success of this approach. In the ten years preceding the development of a community education program in Revelstoke, 16 grizzlies were destroyed and a further 107 were relocated away from the town. An education program run by Revelstoke Bear Aware was put in place in 1996. Since the program began just four grizzlies have been eliminated and five have been relocated.


title: Grizzly bear

text: For back-country campers, hanging food between trees at a height unreachable to bears is a common procedure, although some grizzlies can climb and reach hanging food in other ways. An alternative to hanging food is to use a bear canister.


title: Grizzly bear

text: Traveling in groups of six or more can significantly reduce the chance of bear-related injuries while hiking in bear country. Grizzly bears are especially dangerous because of the force of their bite, which has been measured at over 8 megapascals (1160 psi). It has been estimated that a bite from a grizzly could even crush a bowling ball.


title: Grizzly bear

text: In the past 20 years in Alaska, ecotourism has boomed. While many people come to Alaska to bear-hunt, the majority come to watch the bears and observe their habits. Some of the best bear viewing in the world occurs on coastal areas of the Alaska Peninsula, including in Lake Clark National Park and Preserve, Katmai National Park and Preserve, and the McNeil River State Game Sanctuary and Refuge. Here bears gather in large numbers to feast on concentrated food sources, including sedges in the salt marshes, clams in the nearby tidal flats, salmon in the estuary streams, and berries on the neighboring hillsides.


title: Grizzly bear

text: Katmai National Park and Preserve is one of the best spots to view brown bears. The bear population in Katmai is estimated at a healthy 2,100. The park is located on the Alaskan Peninsula about southwest of the city of Anchorage. At Brooks Camp, a famous site exists where grizzlies can be seen catching salmon from atop a platform—it can be even viewed online from a cam. In coastal areas of the park, such as Hallo Bay, Geographic Harbor, Swikshak Lagoon, American Creek, Big River, Kamishak River, Savonoski River, Moraine Creek, Funnel Creek, Battle Creek, Nantuk Creek, Kukak Bay, and Kaflia Bay bears can be seen fishing alongside wolves, eagles, and river otters. Coastal areas host the highest population densities year round because there is a larger variety of food sources available, but Brooks Camp hosts the highest population (100 bears).


title: Grizzly bear

text: The McNeil River State Game Sanctuary and Refuge, on the McNeil River, is home to the greatest concentration of brown bears in the world. An estimated 144 individual bears have been identified at the falls in a single summer with as many as 74 at one time; 60 or more bears at the falls is a frequent sight, and it is not uncommon to see 100 bears at the falls throughout a single day. The McNeil River State Game Refuge, containing Chenik Lake and a smaller number of grizzly bears, has been closed to grizzly hunting since 1995. All of the Katmai-McNeil area is closed to hunting except for Katmai National Preserve, where regulated legal hunting takes place. In all, the Katmai-McNeil area has an estimated 2,500 grizzly bears.


title: Grizzly bear

text: Admiralty Island, in southeast Alaska, was known to early natives as "Xootsnoowú", meaning "fortress of bears," and is home to the densest grizzly population in North America. An estimated 1600 grizzlies live on the island, which itself is only long. One place to view grizzly bears in the island is probably Pack Creek, in the Stan Price State Wildlife Sanctuary. 20 to 30 grizzlies can be observed at the creek at one time and like Brooks Camp, visitors can watch bears from an above platform. Kodiak Island, hence its name, is another place to view bears. An estimated 3,500 Kodiak grizzly bears inhabit the island, 2,300 of these in the Kodiak National Wildlife Refuge. The O'Malley River is considered the best place on Kodiak Island to view grizzly bears.


title: Grizzly bear

text: The grizzly bear is listed as threatened in the contiguous United States and endangered in parts of Canada. In May 2002, the Canadian Species at Risk Act listed the Prairie population (Alberta, Saskatchewan and Manitoba range) of grizzly bears as extirpated in Canada. As of 2002, grizzly bears were listed as special concern under the COSEWIC registry and considered threatened under the U.S. Fish and Wildlife Service.


title: Grizzly bear

text: Within the United States, the U.S. Fish and Wildlife Service concentrates its effort to restore grizzly bears in six recovery areas. These are Northern Continental Divide (Montana), Yellowstone (Montana, Wyoming, and Idaho), Cabinet-Yaak (Montana and Idaho), Selway-Bitterroot (Montana and Idaho), Selkirk (Idaho and Washington), and North Cascades (Washington). The grizzly population in these areas is estimated at 750 in the Northern Continental Divide, 550 in Yellowstone, 40 in the Yaak portion of the Cabinet-Yaak, and 15 in the Cabinet portion (in northwestern Montana), 105 in Selkirk region of Idaho, 10–20 in the North Cascades, and none currently in Selway-Bitterroots, although there have been sightings. These are estimates because bears move in and out of these areas. In the recovery areas that adjoin Canada, bears also move back and forth across the international boundary.


title: Grizzly bear

text: The U.S. Fish and Wildlife Service claims the Cabinet-Yaak and Selkirk areas are linked through British Columbia, a claim that is disputed. U.S. and Canadian national parks, such as Banff National Park, Yellowstone and Grand Teton, and Theodore Roosevelt National Park are subject to laws and regulations designed to protect the bears.


title: Grizzly bear

text: On 9 January 2006, the US Fish and Wildlife Service proposed to remove Yellowstone grizzlies from the list of threatened and protected species. In March 2007, the U.S. Fish and Wildlife Service "de-listed" the population, effectively removing Endangered Species Act protections for grizzlies in the Yellowstone National Park area. Several environmental organizations, including the NRDC, brought a lawsuit against the federal government to relist the grizzly bear. On 22 September 2009, U.S. District Judge Donald W. Molloy reinstated protection due to the decline of whitebark pine tree, whose nuts are an important source of food for the bears. In early March 2016, the U.S. Fish and Wildlife Service proposed to withdraw Endangered Species Act protections from grizzly bears in and around Yellowstone National Park. The population has risen from 136 bears in 1975 to an estimated 700 in 2017, and was "delisted" in June 2017. It was argued that the population had sufficiently recovered from the threat of extinction, however numerous conservation and tribal organizations argued that the grizzly population remained genetically vulnerable. They successfully sued the administration ("Crow Tribe et al v. Zinke") and on July 30, 2019, the Yellowstone grizzly was officially returned to federal protection.


title: Grizzly bear

text: Farther north, in Alberta, Canada, intense DNA hair-snagging studies in 2000 showed the grizzly population to be increasing faster than what it was formerly believed to be, and Alberta Sustainable Resource Development calculated a population of 841 bears. In 2002, the Endangered Species Conservation Committee recommended that the Alberta grizzly bear population be designated as threatened due to recent estimates of grizzly bear mortality rates that indicated the population was in decline. A recovery plan released by the provincial government in March 2008 indicated the grizzly population is lower than previously believed. In 2010, the provincial government formally listed its population of about 700 grizzlies as "Threatened".


title: Grizzly bear

text: Environment Canada consider the grizzly bear to a "special concern" species, as it is particularly sensitive to human activities and natural threats. In Alberta and British Columbia, the species is considered to be at risk. In 2008, it was estimated there were 16,014 grizzly bears in the British Columbia population, which was lower than previously estimated due to refinements in the population model.


title: Grizzly bear

text: Conservation efforts have become an increasingly vital investment over recent decades, as population numbers have dramatically declined. Establishment of parks and protected areas are one of the main focuses currently being tackled to help reestablish the low grizzly bear population in British Columbia. One example of these efforts is the Khutzeymateen Grizzly Bear Sanctuary located along the north coast of British Columbia; at in size, it is composed of key habitat for this threatened species. Regulations such as limited public access, as well as a strict no hunting policy, have enabled this location to be a safe haven for local grizzlies in the area. When choosing the location of a park focused on grizzly bear conservation, factors such as habitat quality and connectivity to other habitat patches are considered.


title: Grizzly bear

text: The Refuge for Endangered Wildlife located on Grouse Mountain in Vancouver is an example of a different type of conservation effort for the diminishing grizzly bear population. The refuge is a five-acre terrain which has functioned as a home for two orphaned grizzly bears since 2001. The purpose of this refuge is to provide awareness and education to the public about grizzly bears, as well as providing an area for research and observation of this secluded species.


title: Grizzly bear

text: Another factor currently being taken into consideration when designing conservation plans for future generations are anthropogenic barriers in the form of urban development and roads. These elements are acting as obstacles, causing fragmentation of the remaining grizzly bear population habitat and prevention of gene flow between subpopulations (for example, Banff National Park). This, in turn, is creating a decline in genetic diversity, and therefore the overall fitness of the general population is lowered. In light of these issues, conservation plans often include migration corridors by way of long strips of "park forest" to connect less developed areas, or by way of tunnels and overpasses over busy roads. Using GPS collar tracking, scientists can study whether or not these efforts are actually making a positive contribution towards resolving the problem. To date, most corridors are found to be infrequently used, and thus genetic isolation is currently occurring, which can result in inbreeding and therefore an increased frequency of deleterious genes through genetic drift. Current data suggest female grizzly bears are disproportionately less likely than males to use these corridors, which can prevent mate access and decrease the number of offspring.


title: Grizzly bear

text: In the United States, national efforts have been made since 1982 for the recovery plan of grizzly bears. A lot of the efforts made have been through different organizations efforts to educate the public on grizzly bear safety, habits of grizzly bears and different ways to reduce human-bear conflict. The Interagency Grizzly Bear Recovery Committee is one of many organizations committed to the recovery of grizzly bears in the lower 48 states. There are five recovery zones for grizzly bears in the lower 48 states including the North Cascades ecosystem in Washington state. The National Park Service and U.S. Fish and Wildlife initiated the process of an environmental impact statement that started in the fall of 2014 to begin the recovery process of grizzly bears to the North Cascades region. A final plan and environmental impact statement was released in the spring of 2017 with a record of decision to follow.


title: Grizzly bear

text: In 2017, the Trump administration stripped parklands of previous regulations that protected wildlife living on the land, putting species such as the grizzly bear at risk. Specifically, federal protections on the grizzly bear in Yellowstone National Parks were removed. Regulations that protected the bears against hunting methods with Park Service rules (specifically in park lands in Alaska) were revisited by the Department of Interior. The National Parks Conservation Association (NPCA) supports common sense opportunities for hunting in national preserves," but the state of Alaska’s wildlife management leads for the killing of more bears, which increases the population of moose and caribou. The rise in moose and caribou works in favor of sport hunters. Theresa Pierno, President and CEO of National Parks Conservation Association stated, "The State of Alaska’s lawsuit against the Park Service and Fish and Wildlife Service seeks to overturn common sense regulations, which underwent a thorough and transparent public process. More than 70,000 Americans said ‘no’ to baiting bears with grease-soaked donuts in Denali National Park and Preserve. The public was right to want to stop sport hunters from crawling into bears’ dens and using flashlights to wake and kill mother bears and their cubs. The state’s attempt to dismantle the results of this public process jeopardizes the stewardship of federal public lands, which belong to all Americans."


title: Grizzly bear

text: A press release on October 3, 2022 stated that a federal district court, based in Alaska, will be returning to look over a National Park Service rule relating to hunting practices, including baiting bears. The Interior Department and Park Service’s decision permits the law to reside in place while conducting revisions.


title: Laser

text: A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow.


title: Laser

text: A laser differs from other sources of light in that it emits light which is "coherent". Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances (collimation), enabling applications such as laser pointers and lidar (light detection and ranging). Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum. Alternatively, temporal coherence can be used to produce ultrashort pulses of light with a broad spectrum but durations as short as a femtosecond.


title: Laser

text: Lasers are used in optical disc drives, laser printers, barcode scanners, DNA sequencing instruments, fiber-optic and free-space optical communication, semiconducting chip manufacturing (photolithography), laser surgery and skin treatments, cutting and welding materials, military and law enforcement devices for marking targets and measuring range and speed, and in laser lighting displays for entertainment. Semiconductor lasers in the blue to near-UV have also been used in place of light-emitting diodes (LEDs) to excite fluorescence as a white light source. This permits a much smaller emitting area due to the much greater radiance of a laser and avoids the droop suffered by LEDs; such devices are already used in some car headlamps.


title: Laser

text: Lasers are distinguished from other light sources by their coherence. Spatial (or transverse) coherence is typically expressed through the output being a narrow beam, which is diffraction-limited. Laser beams can be focused to very tiny spots, achieving a very high irradiance, or they can have very low divergence in order to concentrate their power at a great distance. Temporal (or longitudinal) coherence implies a polarized wave at a single frequency, whose phase is correlated over a relatively great distance (the coherence length) along the beam. A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase that vary randomly with respect to time and position, thus having a short coherence length.


title: Laser

text: Lasers are characterized according to their wavelength in a vacuum. Most "single wavelength" lasers actually produce radiation in several "modes" with slightly different wavelengths. Although temporal coherence implies some degree of monochromaticity, there are lasers that emit a broad spectrum of light or emit different wavelengths of light simultaneously. Some lasers are not single spatial mode and have light beams that diverge more than is required by the diffraction limit. All such devices are classified as "lasers" based on the method of producing light by stimulated emission. Lasers are employed where light of the required spatial or temporal coherence can not be produced using simpler technologies.


title: Laser

text: The first device using amplification by stimulated emission operated at microwave frequencies, and was named "maser", an acronym for "microwave amplification by stimulated emission of radiation". When similar optical devices were developed they were first known as "optical masers", until "microwave" was replaced by "light" in the acronym.


title: Laser

text: All such devices operating at frequencies higher than microwaves are called lasers (including "infrared laser", "ultraviolet laser", "X-ray laser" and "gamma-ray laser"). All devices operating at microwave or lower radio frequencies are called masers.


title: Laser

text: A laser that produces light by itself is technically an optical oscillator rather than an optical amplifier as suggested by the acronym. It has been humorously noted that the acronym LOSER, for "light oscillation by stimulated emission of radiation", would have been more correct. With the widespread use of the original acronym as a common noun, optical amplifiers have come to be referred to as "laser amplifiers".


title: Laser

text: The back-formed verb "to lase" is frequently used in the field, meaning "to give off coherent light," especially in reference to the gain medium of a laser; when a laser is operating it is said to be "lasing". The words "laser" and "maser" are also used in cases where there is a coherent state unconnected with any manufactured device, as in "astrophysical maser" and "atom laser".


title: Laser

text: A laser consists of a gain medium, a mechanism to energize it, and something to provide optical feedback. The gain medium is a material with properties that allow it to amplify light by way of stimulated emission. Light of a specific wavelength that passes through the gain medium is amplified (increases in power). Feedback enables stimulated emission to amplify predominantly the optical frequency at the peak of the gain-frequency curve. As stimulated emission grows, eventually one frequency dominates over all others, meaning that a coherent beam has been formed. The process of stimulated emission is analogous to that of an audio oscillator with positive feedback which can occur, for example, when the speaker in a public-address system is placed in proximity to the microphone. The screech one hears is audio oscillation at the peak of the gain-frequency curve for the amplifier.


title: Laser

text: For the gain medium to amplify light, it needs to be supplied with energy in a process called pumping. The energy is typically supplied as an electric current or as light at a different wavelength. Pump light may be provided by a flash lamp or by another laser.


title: Laser

text: The most common type of laser uses feedback from an optical cavity—a pair of mirrors on either end of the gain medium. Light bounces back and forth between the mirrors, passing through the gain medium and being amplified each time. Typically one of the two mirrors, the output coupler, is partially transparent. Some of the light escapes through this mirror. Depending on the design of the cavity (whether the mirrors are flat or curved), the light coming out of the laser may spread out or form a narrow beam. In analogy to electronic oscillators, this device is sometimes called a "laser oscillator".


title: Laser

text: Most practical lasers contain additional elements that affect properties of the emitted light, such as the polarization, wavelength, and shape of the beam.


title: Laser

text: Electrons and how they interact with electromagnetic fields are important in our understanding of chemistry and physics.


title: Laser

text: In the classical view, the energy of an electron orbiting an atomic nucleus is larger for orbits further from the nucleus of an atom. However, quantum mechanical effects force electrons to take on discrete positions in orbitals. Thus, electrons are found in specific energy levels of an atom, two of which are shown below:


title: Laser

text: An electron in an atom can absorb energy from light (photons) or heat (phonons) only if there is a transition between energy levels that matches the energy carried by the photon or phonon. For light, this means that any given transition will only absorb one particular wavelength of light. Photons with the correct wavelength can cause an electron to jump from the lower to the higher energy level. The photon is consumed in this process.


title: Laser

text: When an electron is excited from one state to that at a higher energy level with energy difference ΔE, it will not stay that way forever. Eventually, a photon will be spontaneously created from the vacuum having energy ΔE . Conserving energy, the electron transitions to a lower energy level which is not occupied, with transitions to different levels having different time constants. This process is called "spontaneous emission". Spontaneous emission is a quantum-mechanical effect and a direct physical manifestation of the Heisenberg uncertainty principle. The emitted photon has random direction, but its wavelength matches the absorption wavelength of the transition. This is the mechanism of fluorescence and thermal emission.


title: Laser

text: A photon with the correct wavelength to be absorbed by a transition can also cause an electron to drop from the higher to the lower level, emitting a new photon. The emitted photon exactly matches the original photon in wavelength, phase, and direction. This process is called stimulated emission.


title: Laser

text: The gain medium is put into an excited state by an external source of energy. In most lasers this medium consists of a population of atoms which have been excited into such a state by means of an outside light source, or an electrical field which supplies energy for atoms to absorb and be transformed into their excited states.


title: Laser

text: The gain medium of a laser is normally a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission described above. This material can be of any state: gas, liquid, solid, or plasma. The gain medium absorbs pump energy, which raises some electrons into higher-energy ("excited") quantum states. Particles can interact with light by either absorbing or emitting photons. Emission can be spontaneous or stimulated. In the latter case, the photon is emitted in the same direction as the light that is passing by. When the number of particles in one excited state exceeds the number of particles in some lower-energy state, population inversion is achieved. In this state, the rate of stimulated emission is larger than the rate of absorption of light in the medium, and therefore the light is amplified. A system with this property is called an optical amplifier. When an optical amplifier is placed inside a resonant optical cavity, one obtains a laser.


title: Laser

text: For lasing media with extremely high gain, so-called superluminescence, it is possible for light to be sufficiently amplified in a single pass through the gain medium without requiring a resonator. Although often referred to as a laser (see for example nitrogen laser), the light output from such a device lacks the spatial and temporal coherence achievable with lasers. Such a device cannot be described as an oscillator but rather is a high gain optical amplifier which amplifies its own spontaneous emission. The same mechanism describes so-called astrophysical masers/lasers.


title: Laser

text: The optical resonator is sometimes referred to as an "optical cavity", but this is a misnomer: lasers use open resonators as opposed to the literal cavity that would be employed at microwave frequencies in a maser.


title: Laser

text: The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting back on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption.


title: Laser

text: If the gain (amplification) in the medium is larger than the resonator losses, then the power of the recirculating light can rise exponentially. But each stimulated emission event returns an atom from its excited state to the ground state, reducing the gain of the medium. With increasing beam power the net gain (gain minus loss) reduces to unity and the gain medium is said to be saturated. In a continuous wave (CW) laser, the balance of pump power against gain saturation and cavity losses produces an equilibrium value of the laser power inside the cavity; this equilibrium determines the operating point of the laser. If the applied pump power is too small, the gain will never be sufficient to overcome the cavity losses, and laser light will not be produced. The minimum pump power needed to begin laser action is called the "lasing threshold". The gain medium will amplify any photons passing through it, regardless of direction; but only the photons in a spatial mode supported by the resonator will pass more than once through the medium and receive substantial amplification.


title: Laser

text: In most lasers, lasing begins with spontaneous emission into the lasing mode. This initial light is then amplified by stimulated emission in the gain medium. Stimulated emission produces light that matches the input signal in direction, wavelength, and polarization, whereas the phase of emitted light is 90 degrees in lead of the stimulating light. This, combined with the filtering effect of the optical resonator gives laser light its characteristic coherence, and may give it uniform polarization and monochromaticity, depending on the resonator's design. The fundamental laser linewidth of light emitted from the lasing resonator can be orders of magnitude narrower than the linewidth of light emitted from the passive resonator. Some lasers use a separate injection seeder to start the process off with a beam that is already highly coherent. This can produce beams with a narrower spectrum than would otherwise be possible.


title: Laser

text: In 1963, Roy J. Glauber showed that coherent states are formed from combinations of photon number states, for which he was awarded the Nobel Prize in physics. A coherent beam of light is formed by single-frequency quantum photon states distributed according to a Poisson distribution. As a result, the arrival rate of photons in a laser beam is described by Poisson statistics.


title: Laser

text: Many lasers produce a beam that can be approximated as a Gaussian beam; such beams have the minimum divergence possible for a given beam diameter. Some lasers, particularly high-power ones, produce multimode beams, with the transverse modes often approximated using Hermite–Gaussian or Laguerre-Gaussian functions. Some high power lasers use a flat-topped profile known as a "tophat beam". Unstable laser resonators (not used in most lasers) produce fractal-shaped beams. Specialized optical systems can produce more complex beam geometries, such as Bessel beams and optical vortexes.


title: Laser

text: Near the "waist" (or focal region) of a laser beam, it is highly "collimated": the wavefronts are planar, normal to the direction of propagation, with no beam divergence at that point. However, due to diffraction, that can only remain true well within the Rayleigh range. The beam of a single transverse mode (gaussian beam) laser eventually diverges at an angle which varies inversely with the beam diameter, as required by diffraction theory. Thus, the "pencil beam" directly generated by a common helium–neon laser would spread out to a size of perhaps 500 kilometers when shone on the Moon (from the distance of the earth). On the other hand, the light from a semiconductor laser typically exits the tiny crystal with a large divergence: up to 50°. However even such a divergent beam can be transformed into a similarly collimated beam by means of a lens system, as is always included, for instance, in a laser pointer whose light originates from a laser diode. That is possible due to the light being of a single spatial mode. This unique property of laser light, spatial coherence, cannot be replicated using standard light sources (except by discarding most of the light) as can be appreciated by comparing the beam from a flashlight (torch) or spotlight to that of almost any laser.


title: Laser

text: A laser beam profiler is used to measure the intensity profile, width, and divergence of laser beams.


title: Laser

text: Diffuse reflection of a laser beam from a matte surface produces a speckle pattern with interesting properties.


title: Laser

text: The mechanism of producing radiation in a laser relies on stimulated emission, where energy is extracted from a transition in an atom or molecule. This is a quantum phenomenon that was predicted by Albert Einstein, who derived the relationship between the A coefficient describing spontaneous emission and the B coefficient which applies to absorption and stimulated emission. However, in the case of the free electron laser, atomic energy levels are not involved; it appears that the operation of this rather exotic device can be explained without reference to quantum mechanics.


title: Laser

text: A laser can be classified as operating in either continuous or pulsed mode, depending on whether the power output is essentially continuous over time or whether its output takes the form of pulses of light on one or another time scale. Of course even a laser whose output is normally continuous can be intentionally turned on and off at some rate in order to create pulses of light. When the modulation rate is on time scales much slower than the cavity lifetime and the time period over which energy can be stored in the lasing medium or pumping mechanism, then it is still classified as a "modulated" or "pulsed" continuous wave laser. Most laser diodes used in communication systems fall in that category.


title: Laser

text: Some applications of lasers depend on a beam whose output power is constant over time. Such a laser is known as "continuous-wave" ("CW") laser. Many types of lasers can be made to operate in continuous-wave mode to satisfy such an application. Many of these lasers actually lase in several longitudinal modes at the same time, and beats between the slightly different optical frequencies of those oscillations will, in fact, produce amplitude variations on time scales shorter than the round-trip time (the reciprocal of the frequency spacing between modes), typically a few nanoseconds or less. In most cases, these lasers are still termed "continuous-wave" as their output power is steady when averaged over any longer time periods, with the very high-frequency power variations having little or no impact in the intended application. (However, the term is not applied to mode-locked lasers, where the "intention" is to create very short pulses at the rate of the round-trip time.)


title: Laser

text: For continuous-wave operation, it is required for the population inversion of the gain medium to be continually replenished by a steady pump source. In some lasing media, this is impossible. In some other lasers, it would require pumping the laser at a very high continuous power level, which would be impractical or destroy the laser by producing excessive heat. Such lasers cannot be run in CW mode.


title: Laser

text: Pulsed operation of lasers refers to any laser not classified as continuous wave, so that the optical power appears in pulses of some duration at some repetition rate. This encompasses a wide range of technologies addressing a number of different motivations. Some lasers are pulsed simply because they cannot be run in continuous mode.


title: Laser

text: In other cases, the application requires the production of pulses having as large an energy as possible. Since the pulse energy is equal to the average power divided by the repetition rate, this goal can sometimes be satisfied by lowering the rate of pulses so that more energy can be built up in between pulses. In laser ablation, for example, a small volume of material at the surface of a work piece can be evaporated if it is heated in a very short time, while supplying the energy gradually would allow for the heat to be absorbed into the bulk of the piece, never attaining a sufficiently high temperature at a particular point.


title: Laser

text: Other applications rely on the peak pulse power (rather than the energy in the pulse), especially in order to obtain nonlinear optical effects. For a given pulse energy, this requires creating pulses of the shortest possible duration utilizing techniques such as Q-switching.


title: Laser

text: The optical bandwidth of a pulse cannot be narrower than the reciprocal of the pulse width. In the case of extremely short pulses, that implies lasing over a considerable bandwidth, quite contrary to the very narrow bandwidths typical of CW lasers. The lasing medium in some "dye lasers" and "vibronic solid-state lasers" produces optical gain over a wide bandwidth, making a laser possible which can thus generate pulses of light as short as a few femtoseconds (10 s).


title: Laser

text: In a Q-switched laser, the population inversion is allowed to build up by introducing loss inside the resonator which exceeds the gain of the medium; this can also be described as a reduction of the quality factor or 'Q' of the cavity. Then, after the pump energy stored in the laser medium has approached the maximum possible level, the introduced loss mechanism (often an electro- or acousto-optical element) is rapidly removed (or that occurs by itself in a passive device), allowing lasing to begin which rapidly obtains the stored energy in the gain medium. This results in a short pulse incorporating that energy, and thus a high peak power.


title: Laser

text: A mode-locked laser is capable of emitting extremely short pulses on the order of tens of picoseconds down to less than 10 femtoseconds. These pulses repeat at the round-trip time, that is, the time that it takes light to complete one round trip between the mirrors comprising the resonator. Due to the Fourier limit (also known as energy–time uncertainty), a pulse of such short temporal length has a spectrum spread over a considerable bandwidth. Thus such a gain medium must have a gain bandwidth sufficiently broad to amplify those frequencies. An example of a suitable material is titanium-doped, artificially grown sapphire (Ti:sapphire), which has a very wide gain bandwidth and can thus produce pulses of only a few femtoseconds duration.


title: Laser

text: Such mode-locked lasers are a most versatile tool for researching processes occurring on extremely short time scales (known as femtosecond physics, femtosecond chemistry and ultrafast science), for maximizing the effect of nonlinearity in optical materials (e.g. in second-harmonic generation, parametric down-conversion, optical parametric oscillators and the like). Unlike the giant pulse of a Q-switched laser, consecutive pulses from a mode-locked laser are phase-coherent, that is, the pulses (and not just their envelopes) are identical and perfectly periodic. For this reason, and the extremely large peak powers attained by such short pulses, such lasers are invaluable in certain areas of research.


title: Laser

text: Another method of achieving pulsed laser operation is to pump the laser material with a source that is itself pulsed, either through electronic charging in the case of flash lamps, or another laser which is already pulsed. Pulsed pumping was historically used with dye lasers where the inverted population lifetime of a dye molecule was so short that a high energy, fast pump was needed. The way to overcome this problem was to charge up large capacitors which are then switched to discharge through flashlamps, producing an intense flash. Pulsed pumping is also required for three-level lasers in which the lower energy level rapidly becomes highly populated preventing further lasing until those atoms relax to the ground state. These lasers, such as the excimer laser and the copper vapor laser, can never be operated in CW mode.


title: Laser

text: In 1917, Albert Einstein established the theoretical foundations for the laser and the maser in the paper "Zur Quantentheorie der Strahlung" (On the Quantum Theory of Radiation) via a re-derivation of Max Planck's law of radiation, conceptually based upon probability coefficients (Einstein coefficients) for the absorption, spontaneous emission, and stimulated emission of electromagnetic radiation. In 1928, Rudolf W. Ladenburg confirmed the existence of the phenomena of stimulated emission and negative absorption. In 1939, Valentin A. Fabrikant predicted the use of stimulated emission to amplify "short" waves. In 1947, Willis E. Lamb and R.C. Retherford found apparent stimulated emission in hydrogen spectra and effected the first demonstration of stimulated emission. In 1950, Alfred Kastler (Nobel Prize for Physics 1966) proposed the method of optical pumping, which was experimentally demonstrated two years later by Brossel, Kastler, and Winter.


title: Laser

text: In 1951, Joseph Weber submitted a paper on using stimulated emissions to make a microwave amplifier to the June 1952 Institute of Radio Engineers Vacuum Tube Research Conference at Ottawa, Ontario, Canada. After this presentation, RCA asked Weber to give a seminar on this idea, and Charles Hard Townes asked him for a copy of the paper.


title: Laser

text: In 1953, Charles Hard Townes and graduate students James P. Gordon and Herbert J. Zeiger produced the first microwave amplifier, a device operating on similar principles to the laser, but amplifying microwave radiation rather than infrared or visible radiation. Townes's maser was incapable of continuous output. Meanwhile, in the Soviet Union, Nikolay Basov and Aleksandr Prokhorov were independently working on the quantum oscillator and solved the problem of continuous-output systems by using more than two energy levels. These gain media could release stimulated emissions between an excited state and a lower excited state, not the ground state, facilitating the maintenance of a population inversion. In 1955, Prokhorov and Basov suggested optical pumping of a multi-level system as a method for obtaining the population inversion, later a main method of laser pumping.


title: Laser

text: Townes reports that several eminent physicists—among them Niels Bohr, John von Neumann, and Llewellyn Thomas—argued the maser violated Heisenberg's uncertainty principle and hence could not work. Others such as Isidor Rabi and Polykarp Kusch expected that it would be impractical and not worth the effort. In 1964 Charles H. Townes, Nikolay Basov, and Aleksandr Prokhorov shared the Nobel Prize in Physics, "for fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the maser–laser principle".


title: Laser

text: In April 1957, Japanese engineer Jun-ichi Nishizawa proposed the concept of a "semiconductor optical maser" in a patent application.


title: Laser

text: That same year, Charles Hard Townes and Arthur Leonard Schawlow, then at Bell Labs, began a serious study of infrared "optical masers". As ideas developed, they abandoned infrared radiation to instead concentrate on visible light. In 1958, Bell Labs filed a patent application for their proposed optical maser; and Schawlow and Townes submitted a manuscript of their theoretical calculations to the "Physical Review", which was published in 1958.


title: Laser

text: Simultaneously, at Columbia University, graduate student Gordon Gould was working on a doctoral thesis about the energy levels of excited thallium. When Gould and Townes met, they spoke of radiation emission, as a general subject; afterwards, in November 1957, Gould noted his ideas for a "laser", including using an open resonator (later an essential laser-device component). Moreover, in 1958, Prokhorov independently proposed using an open resonator, the first published appearance of this idea. Meanwhile, Schawlow and Townes had decided on an open-resonator laser design – apparently unaware of Prokhorov's publications and Gould's unpublished laser work.


title: Laser

text: At a conference in 1959, Gordon Gould first published the acronym "LASER" in the paper "The LASER, Light Amplification by Stimulated Emission of Radiation". Gould's intention was that different "-ASER" acronyms should be used for different parts of the spectrum: "XASER" for x-rays, "UVASER" for ultraviolet, etc. "LASER" ended up becoming the generic term for non-microwave devices, although "RASER" was briefly popular for denoting radio-frequency-emitting devices.


title: Laser

text: Gould's notes included possible applications for a laser, such as spectrometry, interferometry, radar, and nuclear fusion. He continued developing the idea, and filed a patent application in April 1959. The U.S. Patent Office denied his application, and awarded a patent to Bell Labs, in 1960. That provoked a twenty-eight-year lawsuit, featuring scientific prestige and money as the stakes. Gould won his first minor patent in 1977, yet it was not until 1987 that he won the first significant patent lawsuit victory, when a Federal judge ordered the U.S. Patent Office to issue patents to Gould for the optically pumped and the gas discharge laser devices. The question of just how to assign credit for inventing the laser remains unresolved by historians.


title: Laser

text: On May 16, 1960, Theodore H. Maiman operated the first functioning laser at Hughes Research Laboratories, Malibu, California, ahead of several research teams, including those of Townes, at Columbia University, Arthur Schawlow, at Bell Labs, and Gould, at the TRG (Technical Research Group) company. Maiman's functional laser used a flashlamp-pumped synthetic ruby crystal to produce red laser light at 694 nanometers wavelength. The device was only capable of pulsed operation, due to its three-level pumping design scheme. Later that year, the Iranian physicist Ali Javan, and William R. Bennett, and Donald Herriott, constructed the first gas laser, using helium and neon that was capable of continuous operation in the infrared (U.S. Patent 3,149,290); later, Javan received the Albert Einstein World Award of Science in 1993. Basov and Javan proposed the semiconductor laser diode concept. In 1962, Robert N. Hall demonstrated the first "laser diode" device, which was made of gallium arsenide and emitted in the near-infrared band of the spectrum at 850 nm. Later that year, Nick Holonyak, Jr. demonstrated the first semiconductor laser with a visible emission. This first semiconductor laser could only be used in pulsed-beam operation, and when cooled to liquid nitrogen temperatures (77 K). In 1970, Zhores Alferov, in the USSR, and Izuo Hayashi and Morton Panish of Bell Telephone Laboratories also independently developed room-temperature, continual-operation diode lasers, using the heterojunction structure.


title: Laser

text: Since the early period of laser history, laser research has produced a variety of improved and specialized laser types, optimized for different performance goals, including:


title: Laser

text: In 2015, researchers made a white laser, whose light is modulated by a synthetic nanosheet made out of zinc, cadmium, sulfur, and selenium that can emit red, green, and blue light in varying proportions, with each wavelength spanning 191 nm.


title: Laser

text: In 2017, researchers at TU Delft demonstrated an AC Josephson junction microwave laser. Since the laser operates in the superconducting regime, it is more stable than other semiconductor-based lasers. The device has potential for applications in quantum computing. In 2017, researchers at TU Munich demonstrated the smallest mode locking laser capable of emitting pairs of phase-locked picosecond laser pulses with a repetition frequency up to 200 GHz.


title: Laser

text: In 2017, researchers from the Physikalisch-Technische Bundesanstalt (PTB), together with US researchers from JILA, a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder, established a new world record by developing an erbium-doped fiber laser with a linewidth of only 10 millihertz.


title: Laser

text: Following the invention of the HeNe gas laser, many other gas discharges have been found to amplify light coherently.


title: Laser

text: Gas lasers using many different gases have been built and used for many purposes. The helium–neon laser (HeNe) is able to operate at a number of different wavelengths, however the vast majority are engineered to lase at 633 nm; these relatively low cost but highly coherent lasers are extremely common in optical research and educational laboratories. Commercial carbon dioxide (CO) lasers can emit many hundreds of watts in a single spatial mode which can be concentrated into a tiny spot. This emission is in the thermal infrared at 10.6 µm; such lasers are regularly used in industry for cutting and welding. The efficiency of a CO laser is unusually high: over 30%. Argon-ion lasers can operate at a number of lasing transitions between 351 and 528.7 nm. Depending on the optical design one or more of these transitions can be lasing simultaneously; the most commonly used lines are 458 nm, 488 nm and 514.5 nm. A nitrogen transverse electrical discharge in gas at atmospheric pressure (TEA) laser is an inexpensive gas laser, often home-built by hobbyists, which produces rather incoherent UV light at 337.1 nm. Metal ion lasers are gas lasers that generate deep ultraviolet wavelengths. Helium-silver (HeAg) 224 nm and neon-copper (NeCu) 248 nm are two examples. Like all low-pressure gas lasers, the gain media of these lasers have quite narrow oscillation linewidths, less than 3 GHz (0.5 picometers), making them candidates for use in fluorescence suppressed Raman spectroscopy.


title: Laser

text: Lasing without maintaining the medium excited into a population inversion was demonstrated in 1992 in sodium gas and again in 1995 in rubidium gas by various international teams. This was accomplished by using an external maser to induce "optical transparency" in the medium by introducing and destructively interfering the ground electron transitions between two paths, so that the likelihood for the ground electrons to absorb any energy has been cancelled.


title: Laser

text: Chemical lasers are powered by a chemical reaction permitting a large amount of energy to be released quickly. Such very high power lasers are especially of interest to the military, however continuous wave chemical lasers at very high power levels, fed by streams of gasses, have been developed and have some industrial applications. As examples, in the hydrogen fluoride laser (2700–2900 nm) and the deuterium fluoride laser (3800 nm) the reaction is the combination of hydrogen or deuterium gas with combustion products of ethylene in nitrogen trifluoride.


title: Laser

text: Excimer lasers are a special sort of gas laser powered by an electric discharge in which the lasing medium is an excimer, or more precisely an exciplex in existing designs. These are molecules which can only exist with one atom in an excited electronic state. Once the molecule transfers its excitation energy to a photon, its atoms are no longer bound to each other and the molecule disintegrates. This drastically reduces the population of the lower energy state thus greatly facilitating a population inversion. Excimers currently used are all ; noble gasses are chemically inert and can only form compounds while in an excited state. Excimer lasers typically operate at ultraviolet wavelengths with major applications including semiconductor photolithography and LASIK eye surgery. Commonly used excimer molecules include ArF (emission at 193 nm), KrCl (222 nm), KrF (248 nm), XeCl (308 nm), and XeF (351 nm).


title: Laser

text: The molecular fluorine laser, emitting at 157 nm in the vacuum ultraviolet is sometimes referred to as an excimer laser, however this appears to be a misnomer inasmuch as F is a stable compound.


title: Laser

text: Solid-state lasers use a crystalline or glass rod which is "doped" with ions that provide the required energy states. For example, the first working laser was a ruby laser, made from ruby (chromium-doped corundum). The population inversion is actually maintained in the dopant. These materials are pumped optically using a shorter wavelength than the lasing wavelength, often from a flashtube or from another laser. The usage of the term "solid-state" in laser physics is narrower than in typical use. Semiconductor lasers (laser diodes) are typically "not" referred to as solid-state lasers.


title: Laser

text: Neodymium is a common dopant in various solid-state laser crystals, including yttrium orthovanadate (Nd:YVO), yttrium lithium fluoride () and yttrium aluminium garnet (). All these lasers can produce high powers in the infrared spectrum at 1064 nm. They are used for cutting, welding and marking of metals and other materials, and also in spectroscopy and for pumping dye lasers. These lasers are also commonly frequency doubled, tripled or quadrupled to produce 532 nm (green, visible), 355 nm and 266 nm (UV) beams, respectively. Frequency-doubled diode-pumped solid-state (DPSS) lasers are used to make bright green laser pointers.


title: Laser

text: Ytterbium, holmium, thulium, and erbium are other common "dopants" in solid-state lasers. Ytterbium is used in crystals such as Yb:YAG, Yb:KGW, Yb:KYW, Yb:SYS, Yb:BOYS, Yb:CaF, typically operating around 1020–1050 nm. They are potentially very efficient and high powered due to a small quantum defect. Extremely high powers in ultrashort pulses can be achieved with Yb:YAG. Holmium-doped YAG crystals emit at 2097 nm and form an efficient laser operating at infrared wavelengths strongly absorbed by water-bearing tissues. The Ho-YAG is usually operated in a pulsed mode, and passed through optical fiber surgical devices to resurface joints, remove rot from teeth, vaporize cancers, and pulverize kidney and gall stones.


title: Laser

text: Titanium-doped sapphire (Ti:sapphire) produces a highly tunable infrared laser, commonly used for spectroscopy. It is also notable for use as a mode-locked laser producing ultrashort pulses of extremely high peak power.


title: Laser

text: Thermal limitations in solid-state lasers arise from unconverted pump power that heats the medium. This heat, when coupled with a high thermo-optic coefficient (d"n"/d"T") can cause thermal lensing and reduce the quantum efficiency. Diode-pumped thin disk lasers overcome these issues by having a gain medium that is much thinner than the diameter of the pump beam. This allows for a more uniform temperature in the material. Thin disk lasers have been shown to produce beams of up to one kilowatt.


title: Laser

text: Solid-state lasers or laser amplifiers where the light is guided due to the total internal reflection in a single mode optical fiber are instead called fiber lasers. Guiding of light allows extremely long gain regions providing good cooling conditions; fibers have high surface area to volume ratio which allows efficient cooling. In addition, the fiber's waveguiding properties tend to reduce thermal distortion of the beam. Erbium and ytterbium ions are common active species in such lasers.


title: Laser

text: Quite often, the fiber laser is designed as a double-clad fiber. This type of fiber consists of a fiber core, an inner cladding and an outer cladding. The index of the three concentric layers is chosen so that the fiber core acts as a single-mode fiber for the laser emission while the outer cladding acts as a highly multimode core for the pump laser. This lets the pump propagate a large amount of power into and through the active inner core region, while still having a high numerical aperture (NA) to have easy launching conditions.


title: Laser

text: Fiber lasers have a fundamental limit in that the intensity of the light in the fiber cannot be so high that optical nonlinearities induced by the local electric field strength can become dominant and prevent laser operation and/or lead to the material destruction of the fiber. This effect is called photodarkening. In bulk laser materials, the cooling is not so efficient, and it is difficult to separate the effects of photodarkening from the thermal effects, but the experiments in fibers show that the photodarkening can be attributed to the formation of long-living color centers.


title: Laser

text: Photonic crystal lasers are lasers based on nano-structures that provide the mode confinement and the density of optical states (DOS) structure required for the feedback to take place. They are typical micrometer-sized and tunable on the bands of the photonic crystals.


title: Laser

text: Semiconductor lasers are diodes which are electrically pumped. Recombination of electrons and holes created by the applied current introduces optical gain. Reflection from the ends of the crystal form an optical resonator, although the resonator can be external to the semiconductor in some designs.


title: Laser

text: Commercial laser diodes emit at wavelengths from 375 nm to 3500 nm. Low to medium power laser diodes are used in laser pointers, laser printers and CD/DVD players. Laser diodes are also frequently used to optically pump other lasers with high efficiency. The highest power industrial laser diodes, with power up to 20 kW, are used in industry for cutting and welding. External-cavity semiconductor lasers have a semiconductor active medium in a larger cavity. These devices can generate high power outputs with good beam quality, wavelength-tunable narrow-linewidth radiation, or ultrashort laser pulses.


title: Laser

text: In 2012, Nichia and OSRAM developed and manufactured commercial high-power green laser diodes (515/520 nm), which compete with traditional diode-pumped solid-state lasers.


title: Laser

text: Vertical cavity surface-emitting lasers (VCSELs) are semiconductor lasers whose emission direction is perpendicular to the surface of the wafer. VCSEL devices typically have a more circular output beam than conventional laser diodes. As of 2005, only 850 nm VCSELs are widely available, with 1300 nm VCSELs beginning to be commercialized, and 1550 nm devices an area of research. VECSELs are external-cavity VCSELs. Quantum cascade lasers are semiconductor lasers that have an active transition between energy "sub-bands" of an electron in a structure containing several quantum wells.


title: Laser

text: The development of a silicon laser is important in the field of optical computing. Silicon is the material of choice for integrated circuits, and so electronic and silicon photonic components (such as optical interconnects) could be fabricated on the same chip. Unfortunately, silicon is a difficult lasing material to deal with, since it has certain properties which block lasing. However, recently teams have produced silicon lasers through methods such as fabricating the lasing material from silicon and other semiconductor materials, such as indium(III) phosphide or gallium(III) arsenide, materials which allow coherent light to be produced from silicon. These are called hybrid silicon laser. Recent developments have also shown the use of monolithically integrated nanowire lasers directly on silicon for optical interconnects, paving the way for chip level applications. These heterostructure nanowire lasers capable of optical interconnects in silicon are also capable of emitting pairs of phase-locked picosecond pulses with a repetition frequency up to 200 GHz, allowing for on-chip optical signal processing. Another type is a Raman laser, which takes advantage of Raman scattering to produce a laser from materials such as silicon.


title: Laser

text: Dye lasers use an organic dye as the gain medium. The wide gain spectrum of available dyes, or mixtures of dyes, allows these lasers to be highly tunable, or to produce very short-duration pulses (on the order of a few femtoseconds). Although these tunable lasers are mainly known in their liquid form, researchers have also demonstrated narrow-linewidth tunable emission in dispersive oscillator configurations incorporating solid-state dye gain media. In their most prevalent form these solid state dye lasers use dye-doped polymers as laser media.


title: Laser

text: Free-electron lasers, or FELs, generate coherent, high power radiation that is widely tunable, currently ranging in wavelength from microwaves through terahertz radiation and infrared to the visible spectrum, to soft X-rays. They have the widest frequency range of any laser type. While FEL beams share the same optical traits as other lasers, such as coherent radiation, FEL operation is quite different. Unlike gas, liquid, or solid-state lasers, which rely on bound atomic or molecular states, FELs use a relativistic electron beam as the lasing medium, hence the term "free-electron".


title: Laser

text: The pursuit of a high-quantum-energy laser using transitions between isomeric states of an atomic nucleus has been the subject of wide-ranging academic research since the early 1970s. Much of this is summarized in three review articles. This research has been international in scope, but mainly based in the former Soviet Union and the United States. While many scientists remain optimistic that a breakthrough is near, an operational gamma-ray laser is yet to be realized.


title: Laser

text: Some of the early studies were directed toward short pulses of neutrons exciting the upper isomer state in a solid so the gamma-ray transition could benefit from the line-narrowing of Mössbauer effect. In conjunction, several advantages were expected from two-stage pumping of a three-level system. It was conjectured that the nucleus of an atom, embedded in the near field of a laser-driven coherently-oscillating electron cloud would experience a larger dipole field than that of the driving laser. Furthermore, nonlinearity of the oscillating cloud would produce both spatial and temporal harmonics, so nuclear transitions of higher multipolarity could also be driven at multiples of the laser frequency.


title: Laser

text: In September 2007, the BBC News reported that there was speculation about the possibility of using positronium annihilation to drive a very powerful gamma ray laser. Dr. David Cassidy of the University of California, Riverside proposed that a single such laser could be used to ignite a nuclear fusion reaction, replacing the banks of hundreds of lasers currently employed in inertial confinement fusion experiments.


title: Laser

text: Space-based X-ray lasers pumped by a nuclear explosion have also been proposed as antimissile weapons. Such devices would be one-shot weapons.


title: Laser

text: Living cells have been used to produce laser light. The cells were genetically engineered to produce green fluorescent protein, which served as the laser's gain medium. The cells were then placed between two 20 micrometer wide mirrors, which acted as the laser cavity. When the cell was illuminated with blue light, it emitted intense, directed green laser light.


title: Laser

text: Like astrophysical masers, irradiated planetary or stellar gases may amplify light producing a natural laser. Mars, Venus and MWC 349 exhibit this phenomenon.


title: Laser

text: When lasers were invented in 1960, they were called "a solution looking for a problem". Since then, they have become ubiquitous, finding utility in thousands of highly varied applications in every section of modern society, including consumer electronics, information technology, science, medicine, industry, law enforcement, entertainment, and the military. Fiber-optic communication using lasers is a key technology in modern communications, allowing services such as the Internet.


title: Laser

text: The first widely noticeable use of lasers was the supermarket barcode scanner, introduced in 1974. The laserdisc player, introduced in 1978, was the first successful consumer product to include a laser but the compact disc player was the first laser-equipped device to become common, beginning in 1982 followed shortly by laser printers.


title: Laser

text: In 2004, excluding diode lasers, approximately 131,000 lasers were sold with a value of US$2.19 billion. In the same year, approximately 733 million diode lasers, valued at $3.20 billion, were sold.


title: Laser

text: Lasers have many uses in medicine, including laser surgery (particularly eye surgery), laser healing (photobiomodulation therapy), kidney stone treatment, ophthalmoscopy, and cosmetic skin treatments such as acne treatment, cellulite and striae reduction, and hair removal.


title: Laser

text: Lasers are used to treat cancer by shrinking or destroying tumors or precancerous growths. They are most commonly used to treat superficial cancers that are on the surface of the body or the lining of internal organs. They are used to treat basal cell skin cancer and the very early stages of others like cervical, penile, vaginal, vulvar, and non-small cell lung cancer. Laser therapy is often combined with other treatments, such as surgery, chemotherapy, or radiation therapy. Laser-induced interstitial thermotherapy (LITT), or interstitial laser photocoagulation, uses lasers to treat some cancers using hyperthermia, which uses heat to shrink tumors by damaging or killing cancer cells. Lasers are more precise than traditional surgery methods and cause less damage, pain, bleeding, swelling, and scarring. A disadvantage is that surgeons must acquire specialized training and thus it will likely be more expensive than other treatments.


title: Laser

text: In recent years, some hobbyists have taken an interest in lasers. Lasers used by hobbyists are generally of class IIIa or IIIb (see Safety), although some have made their own class IV types. However, compared to other hobbyists, laser hobbyists are far less common, due to the cost and potential dangers involved. Due to the cost of lasers, some hobbyists use inexpensive means to obtain lasers, such as salvaging laser diodes from broken DVD players (red), Blu-ray players (violet), or even higher power laser diodes from CD or DVD burners.


title: Laser

text: Hobbyists have also used surplus lasers taken from retired military applications and modified them for holography. Pulsed ruby and YAG lasers work well for this application.


title: Laser

text: Different applications need lasers with different output powers. Lasers that produce a continuous beam or a series of short pulses can be compared on the basis of their average power. Lasers that produce pulses can also be characterized based on the "peak" power of each pulse. The peak power of a pulsed laser is many orders of magnitude greater than its average power. The average output power is always less than the power consumed.


title: Laser

text: Even the first laser was recognized as being potentially dangerous. Theodore Maiman characterized the first laser as having a power of one "Gillette" as it could burn through one Gillette razor blade. Today, it is accepted that even low-power lasers with only a few milliwatts of output power can be hazardous to human eyesight when the beam hits the eye directly or after reflection from a shiny surface. At wavelengths which the cornea and the lens can focus well, the coherence and low divergence of laser light means that it can be focused by the eye into an extremely small spot on the retina, resulting in localized burning and permanent damage in seconds or even less time.


title: Laser

text: The indicated powers are for visible-light, continuous-wave lasers. For pulsed lasers and invisible wavelengths, other power limits apply. People working with class 3B and class 4 lasers can protect their eyes with safety goggles which are designed to absorb light of a particular wavelength.


title: Laser

text: Infrared lasers with wavelengths longer than about 1.4 micrometers are often referred to as "eye-safe", because the cornea tends to absorb light at these wavelengths, protecting the retina from damage. The label "eye-safe" can be misleading, however, as it applies only to relatively low power continuous wave beams; a high power or Q-switched laser at these wavelengths can burn the cornea, causing severe eye damage, and even moderate power lasers can injure the eye.


title: Laser

text: Lasers can be a hazard to both civil and military aviation, due to the potential to temporarily distract or blind pilots. See Lasers and aviation safety for more on this topic.


title: Laser

text: Cameras based on charge-coupled devices may actually be more sensitive to laser damage than biological eyes.


title: Pancreatitis

text: Pancreatitis is a condition characterized by inflammation of the pancreas. The pancreas is a large organ behind the stomach that produces digestive enzymes and a number of hormones. There are two main types: acute pancreatitis, and chronic pancreatitis. Signs and symptoms of pancreatitis include pain in the upper abdomen, nausea and vomiting. The pain often goes into the back and is usually severe. In acute pancreatitis, a fever may occur, and symptoms typically resolve in a few days. In chronic pancreatitis weight loss, fatty stool, and diarrhea may occur. Complications may include infection, bleeding, diabetes mellitus, or problems with other organs.


title: Pancreatitis

text: The two most common causes of acute pancreatitis are a gallstone blocking the common bile duct after the pancreatic duct has joined; and heavy alcohol use. Other causes include direct trauma, certain medications, infections such as mumps, and tumors. Chronic pancreatitis may develop as a result of acute pancreatitis. It is most commonly due to many years of heavy alcohol use. Other causes include high levels of blood fats, high blood calcium, some medications, and certain genetic disorders, such as cystic fibrosis, among others. Smoking increases the risk of both acute and chronic pancreatitis. Diagnosis of acute pancreatitis is based on a threefold increase in the blood of either amylase or lipase. In chronic pancreatitis, these tests may be normal. Medical imaging such as ultrasound and CT scan may also be useful.


title: Pancreatitis

text: Acute pancreatitis is usually treated with intravenous fluids, pain medication, and sometimes antibiotics. Typically eating and drinking are disallowed, and a nasogastric tube is placed in the stomach. A procedure known as an endoscopic retrograde cholangiopancreatography (ERCP) may be done to examine the distal common bile duct and remove a gallstone if present. In those with gallstones the gallbladder is often also removed. In chronic pancreatitis, in addition to the above, temporary feeding through a nasogastric tube may be used to provide adequate nutrition. Long-term dietary changes and pancreatic enzyme replacement may be required. And occasionally surgery is done to remove parts of the pancreas.


title: Pancreatitis

text: Globally, in 2015 about 8.9 million cases of pancreatitis occurred. This resulted in 132,700 deaths, up from 83,000 deaths in 1990. Acute pancreatitis occurs in about 30 per 100,000 people a year. New cases of chronic pancreatitis develop in about 8 per 100,000 people a year and currently affect about 50 per 100,000 people in the United States. It is more common in men than women. Often chronic pancreatitis starts between the ages of 30 and 40 while it is rare in children. Acute pancreatitis was first described on autopsy in 1882 while chronic pancreatitis was first described in 1946.


title: Pancreatitis

text: The most common symptoms of pancreatitis are severe upper abdominal or left upper quadrant burning pain radiating to the back, nausea, and vomiting that is worse with eating. The physical examination will vary depending on severity and presence of internal bleeding. Blood pressure may be elevated by pain or decreased by dehydration or bleeding. Heart and respiratory rates are often elevated. The abdomen is usually tender but to a lesser degree than the pain itself. As is common in abdominal disease, bowel sounds may be reduced from reflex bowel paralysis. Fever or jaundice may be present. Chronic pancreatitis can lead to diabetes or pancreatic cancer. Unexplained weight loss may occur from a lack of pancreatic enzymes hindering digestion.


title: Pancreatitis

text: Early complications include shock, infection, systemic inflammatory response syndrome, low blood calcium, high blood glucose, and dehydration. Blood loss, dehydration, and fluid leaking into the abdominal cavity (ascites) can lead to kidney failure. Respiratory complications are often severe. Pleural effusion is usually present. Shallow breathing from pain can lead to lung collapse. Pancreatic enzymes may attack the lungs, causing inflammation. Severe inflammation can lead to intra-abdominal hypertension and abdominal compartment syndrome, further impairing renal and respiratory function and potentially requiring management with an open abdomen to relieve the pressure.


title: Pancreatitis

text: Late complications include recurrent pancreatitis and the development of pancreatic pseudocysts—collections of pancreatic secretions that have been walled off by scar tissue. These may cause pain, become infected, rupture and bleed, block the bile duct and cause jaundice, or migrate around the abdomen. Acute necrotizing pancreatitis can lead to a pancreatic abscess, a collection of pus caused by necrosis, liquefaction, and infection. This happens in approximately 3% of cases or almost 60% of cases involving more than two pseudocysts and gas in the pancreas.


title: Pancreatitis

text: Eighty percent of cases of pancreatitis are caused by alcohol or gallstones. Gallstones are the single most common cause of acute pancreatitis. Alcohol is the single most common cause of chronic pancreatitis. Triglyceride levels greater than 1000 mg/dL (11.29 mmol/L) is another cause.


title: Pancreatitis

text: There are seven classes of medications associated with acute pancreatitis: statins, ACE inhibitors, oral contraceptives/hormone replacement therapy (HRT), diuretics, antiretroviral therapy, valproic acid, and oral hypoglycemic agents. Mechanisms of these drugs causing pancreatitis are not known exactly, but it is possible that statins have direct toxic effect on the pancreas or through the long-term accumulation of toxic metabolites. Meanwhile, ACE inhibitors cause angioedema of the pancreas through the accumulation of bradykinin. Birth control pills and HRT cause arterial thrombosis of the pancreas through the accumulation of fat (hypertriglyceridemia). Diuretics such as furosemide have a direct toxic effect on the pancreas. Meanwhile, thiazide diuretics cause hypertriglyceridemia and hypercalcemia, where the latter is the risk factor for pancreatic stones.


title: Pancreatitis

text: HIV infection itself can cause a person to be more likely to get pancreatitis. Meanwhile, antiretroviral drugs may cause metabolic disturbances such as hyperglycemia and hypercholesterolemia, which predisposes to pancreatitis. Valproic acid may have direct toxic effect on the pancreas. There are various oral hypoglycemic agents that contributes to pancreatitis including metformin. But, glucagon-like peptide-1 (GLP-1) is more strongly associated with pancreatitis by promoting inflammation.