Directivity Pattern of OA Signals Accompanying Laser Induced Damage of a Thin Cr Film

Acoustic waves generated by a Q-switched Nd:YAG pulsed laser on a thin Cr film (80 nm) surface were detected in the free air surrounding the sample. The laser radiation caused visible degradation of the film. Deflection of a He-Ne laser probe beam [1,2] at several horizontal and vertical positions was used as a detection method. Dependence of the signal shape and amplitude on horizontal distance from the source was observed as well as amplitude dependence on source diameter. The amplitude directivity pattern also shows observable diminution of the first maxima amplitude at zenithal position.