Solid state lasers are commonly used in field applications where the operating temperature may vary from minus 50° C. to plus 50° C. However, the stimulated emission cross section of the laser material depends on the temperature as described in M. Bass, L. Weichman, S. Vigil, and B. Brickeen, “The temperature dependence of Nd3+ doped solid-state lasers,” IEEE Journal of Quantum Electronics, vol. 39, pp. 741-748, (2003). Therefore, long pulse and active/passive Q-switched solid state lasers are temperature dependent. It has been assumed that the reflectivity of the mirrors in the laser resonators were independent of temperature since the laser mirrors are typically dielectric coatings and do not show a change in reflectivity with temperature in the range of approximately minus 50° C. and approximately plus 50° C. The only temperature dependent quantity in the output energy of the laser was considered to be the stimulated emission cross section. This quantity in such lasers as Nd:YAG and Nd:GSGG lasers decreases with increasing temperature.
An actively Q-switched laser's output energy decreased when the input energy remained constant or increased if the Q-switched laser was pumped to the amplified spontaneous emission limit at different temperatures. In Bass et al., the temperature dependence was analyzed and demonstrated for lasers with mirrors having reflectivities that were independent of temperature. Dielectric coated laser mirror reflectance does not generally vary with temperature. On the other hand, the reflectivity of a VBG will depend on temperature since thermal expansion changes the spacing of the grating planes. The present invention involves the effect of the temperature dependence of the reflectivity of volume Bragg grating (VBG) mirrors on laser performance and using the temperature dependence of mirror reflectivity to produce lasers, such as Nd:YAG lasers, that operate in the field without temperature dependence.
USPTO Backgrounds
USPTO Backgrounds