Abstract

We have measured the thermal lensing characteristics of a- and c-axes alexandrite laser rods using a diode laser operating at 790 nm as a probe and polarization parallel and perpendicular to the b-axis. In the case of c-axis rods, significant differences between the two polarization directions were found. While the average thermal lensing rates are comparable, the thermally induced lensing is much less astigmatic for beams polarized parallel to the b-axis than for those along the a-axis. For a-axis rods, the average lensing rate is 28% less than those of the c-axis but it is more astigmatic when the probe beam is polarized along the b-axis. The thermally induced nonspherical aberrations were also measured by passing probe beams at different radial locations. Similar to the average lensing rate, the a-axis rod was found to have much fewer nonspherical aberrations than the c-axis. The results provide explanations to the resonator stability conditions of the LANL 100-W laser. The results also provide guidelines to the proper choice of alexandrite laser rods for different performance requirements. A theoretical explanation of the observations based on crystal symmetry is discussed. The experimental techniques employed are presented.

© 1986 Optical Society of America