History of spectroscopy

The history of spectroscopy began in India. There are various references wherein the use of spectroscopy was done by Rishis in ancient India. 
This knowledge, however, was considered to be the guidance from Para Brahman or the Universal Source, the head deity in Hinduism, and hence no one claimed the discoveries in their name.
Modern spectroscopy in the Western world started in the 17th century. New designs in optics, specifically prisms, enabled systematic observations of the solar spectrum. Isaac Newton first applied the word "spectrum" to describe the rainbow of colors that combine to form white light. During the early 1800s, Joseph von Fraunhofer conducted experiments with dispersive spectrometers that enabled spectroscopy to become a more precise and quantitative scientific technique. Since then, spectroscopy has played and continues to play a significant role in chemistry, physics and astronomy. Fraunhofer observed and measured dark lines in the Sun's spectrum, which now bear his name although several of them were observed earlier by Wollaston.
Origins and experimental development.
The Romans were already familiar with the ability of a prism to generate a rainbow of colors. Newton is traditionally regarded as the founder of spectroscopy, but he was not the first scientist who studied and reported on the solar spectrum. The works of Athanasius Kircher (1646), Jan Marek Marci (1648), Robert Boyle (1664), and Francesco Maria Grimaldi (1665), predate Newton's optics experiments (1666–1672). Newton published his experiments and theoretical explanations of dispersion of light in his "Opticks". His experiments demonstrated that white light could be split up into component colors by means of a prism and that these components could be recombined to generate white light. He demonstrated that the prism is not imparting or creating the colors but rather separating constituent parts of the white light. Newton's corpuscular theory of light was gradually succeeded by the wave theory. It was not until the 19th century that the quantitative measurement of dispersed light was recognized and standardized. As with many subsequent spectroscopy experiments, Newton's sources of white light included flames and stars, including the Sun. Subsequent studies of the nature of light include those of Hooke, Huygens, Young. Subsequent experiments with prisms provided the first indications that spectra were associated uniquely with chemical constituents. Scientists observed the emission of distinct patterns of colour when salts were added to alcohol flames.
Early 19th century (1800–1829).
In 1802, William Hyde Wollaston built a spectrometer, improving on Newton's model, that included a lens to focus the Sun’s spectrum on a screen. Upon use, Wollaston realized that the colors were not spread uniformly, but instead had missing patches of colors, which appeared as dark bands in the sun's spectrum. At the time, Wollaston believed these lines to be natural boundaries between the colors, but this hypothesis was later ruled out in 1815 by Fraunhofer's work.
Joseph von Fraunhofer made a significant experimental leap forward by replacing a prism with a diffraction grating as the source of wavelength dispersion. Fraunhofer built off the theories of light interference developed by Thomas Young, François Arago and Augustin-Jean Fresnel. He conducted his own experiments to demonstrate the effect of passing light through a single rectangular slit, two slits, and so forth, eventually developing a means of closely spacing thousands of slits to form a diffraction grating. The interference achieved by a diffraction grating both improves the spectral resolution over a prism and allows for the dispersed wavelengths to be quantified. Fraunhofer's establishment of a quantified wavelength scale paved the way for matching spectra observed in multiple laboratories, from multiple sources (flames and the sun) and with different instruments. Fraunhofer made and published systematic observations of the solar spectrum, and the dark bands he observed and specified the wavelengths of are still known as Fraunhofer lines.
Throughout the early 1800s, a number of scientists pushed the techniques and understanding of spectroscopy forward. In the 1820s, both John Herschel and William H. F. Talbot made systematic observations of salts using flame spectroscopy.
Mid-19th century (1830–1869).
In 1835, Charles Wheatstone reported that different metals could be easily distinguished by the different bright lines in the emission spectra of their sparks, thereby introducing an alternative mechanism to flame spectroscopy. In 1849, J. B. L. Foucault experimentally demonstrated that absorption and emission lines appearing at the same wavelength are both due to the same material, with the difference between the two originating from the temperature of the light source. In 1853, the Swedish physicist Anders Jonas Ångström presented observations and theories about gas spectra in his work "Optiska Undersökningar" (Optical investigations) to the [[Royal Swedish Academy of Sciences]]. Ångström postulated that an incandescent gas emits luminous rays of the same wavelength as those it can absorb. Ångström was unaware of Foucalt's experimental results. At the same time [[Sir George Stokes, 1st Baronet|George Stokes]] and [[William Thomson, 1st Baron Kelvin|William Thomson (Kelvin)]] were discussing similar postulates. Ångström also measured the emission spectrum from hydrogen later labeled the [[Balmer lines]]. In 1854 and 1855, [[David Alter]] published observations on the spectra of metals and gases, including an independent observation of the [[Balmer lines]] of hydrogen.
[[Image:Kirchhoffs first spectroscope.jpg|thumb|Spectroscope of Kirchhoff and Bunsen]]
The systematic attribution of spectra to [[chemical element]]s began in the 1860s with the work of German physicists [[Robert Bunsen]] and [[Gustav Kirchhoff]], who found that [[Fraunhofer lines]] correspond to emission spectral lines observed in laboratory light sources. This laid way for spectrochemical analysis in laboratory and astrophysical science. Bunsen and Kirchhoff applied the optical techniques of Fraunhofer, Bunsen's [[Bunsen burner|improved flame source]] and a highly systematic experimental procedure to a detailed examination of the spectra of chemical compounds. They established the linkage between chemical elements and their unique spectral patterns. In the process, they established the technique of analytical spectroscopy. In 1860, they published their findings on the spectra of eight elements and identified these elements' presence in several natural compounds. They demonstrated that spectroscopy could be used for trace chemical analysis and several of the chemical elements they discovered were previously unknown. Kirchhoff and Bunsen also definitively established the link between absorption and emission lines, including attributing solar absorption lines to particular elements based on their corresponding spectra. Kirchhoff went on to contribute fundamental research on the nature of spectral absorption and emission, including what is now known as [[Kirchhoff's law of thermal radiation]]. Kirchhoff's applications of this law to spectroscopy are captured in [[Gustav Kirchhoff#Kirchhoff.27s three laws of spectroscopy|three laws of spectroscopy]]:
In the 1860s the husband-and-wife team of [[William Huggins|William]] and [[Margaret Lindsay Huggins|Margaret Huggins]] used spectroscopy to determine that the stars were composed of the same elements as found on earth. They also used the non-relativistic [[Doppler effect|Doppler shift]] ([[redshift]]) equation on the spectrum of the star [[Sirius]] in 1868 to determine its axial speed. They were the first to take a spectrum of a planetary nebula when the [[Cat's Eye Nebula]] (NGC 6543) was analyzed. Using spectral techniques, they were able to distinguish [[nebula]]e from [[Galaxy|galaxies]].
[[August Beer]] observed a relationship between light absorption and concentration and created the color comparator which was later replaced by a more accurate device called the [[Spectrophotometry|spectrophotometer]].
Late 19th century (1870–1899).
In the 19th century new developments such as the discovery of photography, [[Henry Augustus Rowland|Rowland's]] invention of the concave [[diffraction grating]], and [[Victor Schumann|Schumann's]] works on discovery of [[vacuum ultraviolet]] (fluorite for prisms and lenses, low-gelatin [[photographic plate]]s and absorption of UV in air below 185 [[Nanometre|nm]]) made advance to shorter wavelengths very fast. At the same time [[James Dewar|Dewar]] observed series in alkali spectra, [[Walter Noel Hartley|Hartley]] found constant wave-number differences, [[Johann Jakob Balmer|Balmer]] discovered a relation connecting wavelengths in the visible [[hydrogen]] spectrum, and finally [[Johannes Rydberg|Rydberg]] derived a formula for [[Wavenumber|wave-numbers]] of spectral series.
[[Johann Balmer]] discovered in 1885 that the four visible lines of hydrogen were part of a [[Balmer series|series]] that could be expressed in terms of integers. This was followed a few years later by the [[Rydberg formula]], which described additional series of lines.
Meanwhile, the substantial summary of past experiments performed by [[James Clerk Maxwell|Maxwell]] (1873), resulted in his [[Maxwell's equations|equations of electromagnetic waves]].
In 1895, the German physicist [[Wilhelm Conrad Röntgen]] discovered and extensively studied [[X-ray]]s, which were later used in [[X-ray spectroscopy]]. One year later, in 1896, French physicist [[Antoine Henri Becquerel]] discovered radioactivity, and Dutch physicist [[Pieter Zeeman]] observed spectral lines being split by a magnetic field.
Early 20th century (1900–1950).
The first decade of the 20th century brought the basics of [[Quantum mechanics|quantum theory]] ([[Max Planck|Planck]], [[Albert Einstein|Einstein]]) and interpretation of spectral series of hydrogen by [[Theodore Lyman|Lyman]] in [[Vacuum ultraviolet|VUV]] and by [[Friedrich Paschen|Paschen]] in [[infrared]]. [[Walther Ritz|Ritz]] formulated the [[Rydberg–Ritz combination principle|combination principle]].
In 1913 [[Niels Bohr|Bohr]] formulated his quantum mechanical model of atom. This stimulated empirical term analysis. Bohr published a theory of the hydrogen-like atoms that could explain the observed wavelengths of spectral lines due to electrons transitioning from different energy states. In 1937 "E. Lehrer created the first fully-automated spectrometer" to help more accurately measure spectral lines. With the development of more advanced instruments such as photo-detectors scientists were then able to more accurately measure specific wavelength absorption of substances.
Development of quantum mechanics.
Between 1920 and 1930 fundamental concepts of quantum mechanics were developed by [[Wolfgang Pauli|Pauli]], [[Werner Heisenberg|Heisenberg]], [[Erwin Schrödinger|Schrödinger]], and [[Paul Dirac|Dirac]]. Understanding of the [[Spin (physics)|spin]] and exclusion principle allowed conceiving how [[Electron configuration|electron shells]] of atoms are filled with the increasing [[atomic number]].
Multiply ionized atoms.
This branch of [[spectroscopy]] deals with radiation related to [[atom]]s that are stripped of several electrons (multiply ionized atoms (MIA), multiply charged ions, highly charged [[ion]]s). These are observed in very [[Plasma (physics)|hot plasmas]] (laboratory or astrophysical) or in [[Accelerator physics|accelerator]] experiments ([[Particle accelerator|beam-foil]], [[electron beam ion trap]] (EBIT)). The lowest exited electron shells of such ions decay into stable ground states producing photons in [[Ultraviolet|VUV]], [[Extreme ultraviolet|EUV]] and soft [[X-ray]] spectral regions (so-called resonance transitions).
Structure studies.
Further progress in studies of atomic structure was in tight connection with the advance to shorter [[wavelength]] in EUV region. [[Robert Andrews Millikan|Millikan]], [[Ralph A. Sawyer|Sawyer]], [[Ira Sprague Bowen|Bowen]] used [[electric discharge]]s in vacuum to observe some emission spectral lines down to 13 nm they prescribed to stripped atoms. In 1927 Osgood and Hoag reported on [[Grazing incidence diffraction|grazing incidence]] concave grating spectrographs and photographed lines down to 4.4 nm (Kα of carbon). Dauvillier used a fatty acid crystal of large crystal grating space to extend soft x-ray spectra up to 12.1 nm, and the gap was closed. In the same period [[Manne Siegbahn]] constructed a very sophisticated grazing incidence spectrograph that enabled Ericson and [[Bengt Edlén|Edlén]] to obtain spectra of vacuum spark with high quality and to reliably identify lines of multiply ionized atoms up to O VI, with five stripped electrons. [[Walter Grotrian|Grotrian]] developed his graphic presentation of energy structure of the atoms. [[Henry Norris Russell|Russel]] and Saunders proposed their [[Angular momentum coupling|coupling]] scheme for the spin-orbit interaction and their generally recognized notation for [[Term symbol|spectral terms]].
Accuracy.
Theoretical quantum-mechanical calculations become rather accurate to describe the energy structure of some simple electronic configurations. The results of theoretical developments were summarized by [[Edward Condon|Condon]] and Shortley in 1935.
[[Bengt Edlén|Edlén]] thoroughly analyzed spectra of MIA for many chemical elements and derived regularities in energy structures of MIA for many isoelectronic sequences (ions with the same number of electrons, but different nuclear charges). Spectra of rather high ionization stages (e.g. Cu XIX) were observed.
The most exciting event was in 1942, when [[Bengt Edlén|Edlén]] proved the identification of some solar coronal lines on the basis of his precise analyses of spectra of MIA. This implied that the [[solar corona]] has a temperature of a million degrees, and strongly advanced understanding of solar and stellar physics.
After the [[World War II|WW II]] experiments on balloons and rockets were started to observe the VUV radiation of the Sun. (See [[X-ray astronomy]]). More intense research continued since 1960 including [[spectrometer]]s on satellites.
In the same period the laboratory spectroscopy of MIA becomes relevant as a diagnostic tool for hot plasmas of thermonuclear devices (see [[Nuclear fusion]]) which begun with building [[Stellarator]] in 1951 by Spitzer, and continued with [[tokamak]]s, z-pinches and the laser produced plasmas. Progress in ion [[Accelerator physics|accelerators]] stimulated beam-foil spectroscopy as a means to measure lifetimes of exited states of MIA. Many various data on highly exited energy levels, [[autoionization]] and inner-core ionization states were obtained. 
Electron beam ion trap.
Simultaneously theoretical and computational approaches provided data necessary for identification of new spectra and interpretation of observed line intensities. New laboratory and theoretical data become very useful for spectral observation in space. It was a real upheaval of works on MIA in USA, England, France, Italy, Israel, Sweden, Russia and other countries
A new page in the spectroscopy of MIA may be dated as 1986 with development of [[Electron beam ion trap|EBIT]] (Levine and Marrs, [[Lawrence Livermore National Laboratory|LLNL]]) due to a favorable composition of modern high technologies such as [[cryogenics]], [[ultra-high vacuum]], [[superconducting magnet]]s, powerful [[Electron-beam technology|electron beams]] and [[semiconductor detector]]s. Very quickly EBIT sources were created in many countries (see [[National Institute of Standards and Technology|NIST]] summary for many details as well as reviews.)
A wide field of spectroscopic research with EBIT is enabled including achievement of highest grades of ionization (U92+), wavelength measurement, [[hyperfine structure]] of energy levels, [[Quantum electrodynamics|quantum electrodynamic]] studies, ionization [[Cross section (physics)|cross-sections]] (CS) measurements, electron-impact excitation CS, X-ray [[Polarization (waves)|polarization]], relative line intensities, dielectronic [[Recombination (physics)|recombination]] CS, magnetic octupole decay, lifetimes of [[Forbidden mechanism|forbidden transitions]], charge-exchange recombination, etc.
Infrared and Raman spectroscopy.
Many early scientists who studied the IR spectra of compounds had to develop and build their own instruments to be able to record their measurements making it very difficult to get accurate measurements. During [[World War II]], the U.S. government contracted different companies to develop a method for the polymerization of [[butadiene]] to create [[synthetic rubber|rubber]], but this could only be done through analysis of Ca hydrocarbon isomers. These contracted companies started developing optical instruments and eventually created the first infrared spectrometers. With the development of these commercial spectrometers Infrared Spectroscopy became a more popular method to determine the "fingerprint" for any molecule. Raman spectroscopy was first observed in 1928 by Sir [[C. V. Raman|Chandrasekhara Venkata Raman]] in liquid substances and also by "Grigory Landsberg and Leonid Mandelstam in crystals". Raman spectroscopy is based on the observation of the raman effect which is defined as "The intensity of the scattered light is dependent on the amount of the polarization potential change". The raman spectrum records light intensity vs. light frequency (wavenumber) and the wavenumber shift is characteristic to each individual compound.
Laser spectroscopy.
Laser spectroscopy is a spectroscopic technique that uses [[laser]]s to be able determine the emitted frequencies of matter. The laser was invented because spectroscopists took the concept of its predecessor, the [[maser]], and applied it to the visible and infrared ranges of light. The maser was invented by [[Charles H. Townes|Charles Townes]] and other spectroscopists to stimulate matter to determine the radiative frequencies that specific atoms and molecules emitted. While working on the maser, Townes realized that more accurate detections were possible as the frequency of the microwave emitted increased. This led to an idea a few years later to use the visible and eventually the infrared ranges of light for spectroscopy that became a reality with the help of [[Arthur Leonard Schawlow|Arthur Schawlow]]. Since then, lasers have gone on to significantly advance experimental spectroscopy. The laser light allowed for much higher precision experiments specifically in the uses of studying collisional effects of light as well as being able to accurately detect specific wavelengths and frequencies of light, allowing for the invention of devices such as laser atomic clocks. Lasers also made spectroscopy that used time methods more accurate by using speeds or decay times of photons at specific wavelengths and frequencies to keep time. Laser spectroscopic techniques have been used for many different applications. One example is using laser spectroscopy to detect compounds in materials. One specific method is called Laser-induced Fluorescence Spectroscopy, and uses spectroscopic methods to be able to detect what materials are in a solid, liquid, or gas, "[[in situ]]". This allows for direct testing of materials, instead of having to take the material to a lab to figure out what the solid, liquid, or gas is made of.
External links.
[[Category:Spectroscopy]]
[[Category:Quantum mechanics]]
[[Category:History of chemistry]]
[[Category:History of physics]]
[[Category:Plasma physics]]
[[Category:Ionizing radiation]]