Photoacoustic method for orientation and optical characterization of nonlinear crystals

Second-harmonic conversion of the 532-nm pulsed output of a doubled Nd:YAG laser in KDP was characterized by analyzing the changes in the acoustic sig nals generated in the crystal at different orientation conditions and for S everal incident fluences, Using a piezoelectric transducer, phase-matching condition was determined by maximizing the amplitude of the acoustic signal s detected. The angular orientation for optimum harmonic efficiency was obt ained with the same precision compared with the conventional optical proced ure. The-origin of the photoacoustic signals is the relaxed energy followin g the absorption of 266-nm photons. To determine the mechanisms of the 266- nm absorption processes, we: also performed experiments under direct illumi nation with the 266-nm emission of the quadrupled Nd:YAG laser. A combinati on of a linear and nonlinear process occurs. Direct absorption by KDP as we ll as the participation of transient defects produced in the material were analyzed.