Measurement of thermal lensing in Cr/sup 3+/-doped colquiriites

The first direct measurements of thermally induced lensing in end-pumped Cr/sup 3+/-doped LiSrAlF/sub 6/, LiSrGaAlF/sub 6/, LiSrCaAlF/sub 6/, and LiCaAlF/sub 6/ are reported. Using a sensitive measurement technique, focal lengths as long as 40 m were measured. A thermal model has been created to determine the temperature rise as a function of position inside the laser crystal. This new model calculates the temperature distribution by considering quantum defect, upconversion, and upper state lifetime quenching as heating sources. Thermal lensing in the colquiriites is significantly reduced because of compensation of the temperature-dependent refractive index by the induced photoelastic stress inside the colquiriite crystal.