Laser Scanning Method for Time-Resolved Measurements of Wavefront Distortion Introduced by Active Elements in High-Power Laser Amplifiers

A novel method was proposed for the experimental investigation of wavefront distortion introduced to amplified radiation by pumped active elements in high-power laser amplifiers. The method is based on the simultaneous measurement of temperature distribution and the distribution of population density of the excited laser level in active elements. The underlying theory of the technique was presented; various factors affecting the accuracy of wavefront distortion determination were analyzed. The method was tested to study the wavefront distortion and the depolarization of radiation introduced by the Yb:YAG active element of a cryogenically cooled laser amplifier with high-power diode pumping. The focal length of the thermal lens was 0.40 ± 0.03 and 0.47 ± 0.05 m for the horizontal and vertical planes, respectively. The focal length of the electron lens was two orders of magnitude larger. The maximum value of losses induced by depolarization was 8.5%.