Thermal lensing measurements of Ti: Sapphire crystal pumped at 80 MHz picosecond pulses by Shack-Hartmann wavefront sensor

The thermal lensing effects in the lasing crystal appear to be dominant when the pump laser focused on the lasing crystal which causes the local heating effect. The spatial refractive index variations observed if the crystal has non-uniform temperature distribution. In the present study, the demonstration of thermal lensing effect of Brewster-cut Ti: Sapphire crystal carried out when pumped by 25 ps pulses at 80 MHz repetition rate with 532 nm central wavelength, while the average pump power controlled by the attenuator. The thermal lensing effects measured first at the ~293 K temperature and later at ~40 K by using the cryogenic cooling system. The thermal lensing variations at different average pump power were calculated and measured by using the HASO4 Shack-Hartmann wavefront sensor.