the following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention , its application , or uses . referring now to the figures , a laser welding lens assembly , generally indicated at reference numeral 10 , is provided according to a first embodiment of the present invention . as best seen in fig1 and 2 , laser welding lens assembly 10 includes a fiber optic bundle 12 having a plurality of optical fibers 14 generally arranged in a circular pattern capable of carrying or transmitting radiative energy in the form of a laser beam therethrough . fiber optic bundle 12 is operably coupled to a laser source 16 , such as an infrared laser , according to known principles . laser welding lens assembly 10 further includes a waveguide 18 , a tailored lens 20 , and a window 22 . waveguide 18 is coupled to fiber optic bundle 12 along an interface 24 . fiber optic bundle 12 terminates at an end 26 within waveguide 18 generally adjacent tailored lens 20 . tailored lens 20 is securely retained within waveguide 18 and is capable of redistributing the laser beam in a uniform temperature distribution across a weld zone 28 , which will be discussed in detail below . window 22 is coupled to an end of waveguide 18 and is retained therein to protect tailored lens 20 from environment contaminates and / or damage . in operation , laser source 16 outputs a laser beam that is carried by fiber optic bundle 12 . this laser beam passes through tailored lens 20 and is redistributed to achieve a uniform temperature distribution across weld zone 28 . the laser beam then exits waveguide 18 and passes through a first plastic part 30 , also known as a transmissive piece . transmissive piece 30 generally permits the laser beam to pass therethrough . the laser beam is then absorbed by a second plastic part 32 , also known as an absorptive piece . absorptive piece 32 generally absorbs the radiative energy of the laser beam to produce heat in weld zone 28 . this heat causes transmissive piece 30 and absorptive piece 32 to be melted and thus welded together . still referring to fig1 and 2 , as described above , tailored lens 20 is capable of redistributing the laser beam in a uniform temperature distribution across weld zone 28 . this allows for uniform welding across weld zone 28 and , thus , prevents overheating , bubbling , and / or out - gassing at or near weld zone 28 . the actual cross - sectional design of tailored lens 20 is unique in that it redistributes the laser beam to achieve increased intensity along the edges of weld zone 28 to in turn achieve a uniform temperature distribution across weld zone 28 . turning now to fig3 - 5 , a laser welding lens assembly , generally indicated at reference numeral 10 ′, is provided according to a second embodiment of the present invention . as best seen in fig1 and 2 , laser welding lens assembly 10 ′ includes a fiber optic bundle 12 ′ having a plurality of optical fibers 14 generally arranged in a side - by - side arrangement capable of carrying or transmitting radiative energy in the form of a laser beam therethrough . fiber optic bundle 12 ′ is operably coupled to laser source 16 according to known principles . laser welding lens assembly 10 ′ further includes a linear weld waveguide 34 and a tailored lens 20 ′. linear weld waveguide 35 is coupled to fiber optic bundle 12 ′ along an interface 24 ′. fiber optic bundle 12 ′ terminates at an end 26 ′ within linear weld waveguide 35 generally adjacent tailored lens 20 ′. tailored lens 20 ′ is securely retained within linear weld waveguide 34 and is capable of redistributing the laser beam in a uniform temperature distribution across an elongated weld zone 28 , which will be discussed in detail below . in operation , laser source 16 outputs a laser beam that is carried by fiber optic bundle 12 ′. this laser beam passes through tailored lens 20 ′ and is redistributed into a uniform temperature distribution . the laser beam then exits linear weld waveguide 35 and passes through a first plastic part 30 , also known as a transmissive piece . transmissive piece 30 generally permits the laser beam to pass therethrough . the laser beam is then absorbed by a second plastic part 32 , also known as an absorptive piece . absorptive piece 32 generally absorbs the radiative energy of the laser beam to produce heat in weld zone 28 . this heat causes transmissive piece 30 and absorptive piece 32 to be melted and thus welded together . laser welding lens assembly 10 ′ is capable of producing an elongated laser beam adapted for linear welding applications due to the elongated shape of tailored lens 20 ′. as described above , tailored lens 20 , 20 ′ are capable of redistributing the laser beam in a uniform temperature distribution across weld zone 28 . this allows for uniform welding across weld zone 28 and , thus , prevents overheating , bubbling , and / or out - gassing at or near weld zone 28 . with particular reference to fig1 and 2 , tailored lens 20 is generally cylindrical in shape and includes a flat face 34 and a contoured face 36 . similarly , with reference to fig3 - 5 , tailored lens 20 ′ is generally elongated in shape and includes a flat face 34 ′ and a contoured face 36 ′. it should be understood that flat face 34 , 34 ′ may also be contoured in order to achieve the desired laser beam distribution . the shape of contoured face 36 , 36 ′ is determined through a process of mapping input light ray positions to output light ray positions , which yield the same temperature distribution . this process of determining the exact contour of contoured face 36 , 36 ′ will now be discussed in reference to a single application . with particular reference to fig6 a temperature distribution graph is provided that illustrates the temperature distribution of a uniform - intensity laser beam exiting fiber optic bundle 12 , without the use of tailored lens 20 . it should be appreciated that this temperature distribution is generally - parabolically shaped and , thus , has a higher temperature a in the middle of the distribution than along the edges . this higher temperature in the middle of the distribution may cause the aforementioned overheating , bubbling , and / or out - gassing at or near weld zone 28 . however , in order to achieve a uniform temperature distribution across weld zone 28 , it is first necessary to employ a finite element analysis ( fea ) program to determine the necessary intensity distribution capable of achieving a uniform temperature distribution . accordingly , as seen in fig7 a laser intensity distribution graph is produced that illustrates the laser intensity distribution ( q ) necessary to achieve a uniform temperature ( t ) at weld zone 28 . as can be seen from peaks b and valley c of fig7 it is necessary to direct increased laser intensity to the outer edges of the weld zone 28 , since according to heat transfer principles these outer edges of weld zone 28 require additional laser intensity to raise their temperature as they are surrounded by unheated ( i . e . cooler ) areas . however , the center of weld zone 28 requires comparatively less laser intensity because it is surrounded by heated areas and , thus , will heat up more quickly . in order to derive the light intensity output at the weld ( q x ) for a desired uniform welding temperature ( t ), it is necessary to use the following formula : q x = q *( t − t 0 )/( t x − t 0 ) where q x is the desired light intensity output at a given x position , q is the starting uniform light intensity used in the fea program , t is the desired uniform welding temperature , t x is the temperature at a given x position derived from the fea program , and t 0 is the ambient temperature . if we then assume that the input light has parallel rays , we then use the actual intensity of the input light at a given x position to map the input light ray positions to the output light ray positions to yield a uniform temperature distribution . it is then necessary to calculate the lens slope at a given x position . needed for a given index of refraction to bend the input light ray to the desired output light ray position . these slopes are then integrated to define the lens shape as seen in fig8 . with particular reference to fig8 we can see the desired lens shape for a generally - gaussian distributed input laser beam is a generally concave , divergent lens . however , with closer inspection of the preferred shape of contoured face 36 we see that the preferred shape for this particular application is actually a complex shape — including both convex and concave portions . that is , we can see that the center portion of the curve in fig8 is generally concave shaped between about 0 . 05 inches and 0 . 2 inches having an increasing slope outwardly from its center ( generally indicated at d ). however , the portion of the curve between about 0 - 0 . 05 inches and 0 . 2 - 0 . 25 inches is generally convex having a decreasing slope as we travel outwardly from the center concave portion ( generally indicated at e ). the particular shape of contoured face 36 , however , is dependent upon the particular application parameters set forth in the above equation and thus may vary . applying the above analysis and computation to laser welding lens assembly 10 ′ ( linear weld application ), we see from fig9 that the initial temperature distribution curve for a uniform laser intensity ( q ) is slightly different than that set forth in fig6 . however , we can still see the characteristic domed curve . accordingly , in order to achieve a generally uniform temperature distribution , it is necessary to redistribute the laser light to the edges , as seen by peaks f in fig1 . applying the above equation and computation , a lens shape is again determined for the specific application ( in this case , a linear weld ) as seen in fig1 . as can been seen in fig1 , contoured face 36 ′ is again a complex shape — including both convex and concave portions . that is , the center portion of contoured face 36 ′ is generally concave shaped between about 0 . 03 inches and 0 . 09 inches having an increasing slope outwardly from its center ( generally indicated at g ). the portion of the curve between about 0 - 0 . 03 inches and 0 . 09 - 0 . 13 inches is generally convex having a decreasing slope as we travel outwardly from the center concave portion ( generally indicated at h ). preferably , tailored lens 20 , 20 ′ is made of a silicone material , however tailored lens 20 , 20 ′ may be made of any material typically used in lens construction , including glass , acrylic , plastic , polycarbonate , and the like . an advantage to using silicone , however , is the fact that tailored lens 20 ′ and waveguide 24 ′ can be made or mechanically curved to permit the welding around corners or into tight and / or complex areas . an additional advantage of using silicon is its ability to resist particulates or other debris from sticking thereto . it should be appreciated that although it is preferred that the shape of contoured face 36 , 36 ′ is determined from an analysis and mapping of light intensity to a specific output position , it should be understood that many of the advantages of the present invention may be achieved using a concave divergent lens 50 in combination with a waveguide 51 , as seen in fig1 . concave divergent lens 50 may be a plano - concave , a concave - plano , concave - concave , or any other divergent lens system . the shape of concave divergent lens 50 and the length and inner diameter of waveguide 51 is selected such that as the laser beam exits concave divergent lens 50 , the now cone - shaped laser beam reflects off an inner portion 52 of waveguide 51 . a length 54 of waveguide downstream from concave divergent lens 50 is selected to permit only a predetermined portion of the cone - shaped laser beam to reflect off inner portion to produce a higher laser intensity distribution the edges of weld zone 28 than in the center of weld zone 28 . consequently , as discussed in connection with the previous embodiments , concave divergent lens 50 and waveguide 51 cooperate to tailor the appropriate laser intensity distribution necessary to achieve a uniform temperature distribution across weld zone 28 . the description of the invention is merely exemplary in nature and , thus , variations that do not depart from the gist of the invention are intended to be within the scope of the invention . such variations are not to be regarded as a departure from the spirit and scope of the invention .