Optodynamic observation of double laser-induced breakdown at the water surface

A measurement technique based on the combination of beam deflection probe and photographic detection of optical emission is introduced for the study of laser-induced dielectric breakdown in the vicinity of the air-water interface. The plasma was photographed with a CCD camera and the shock wave generated by the breakdown in the air and inside the water was detected with a beam deflection probe as a function of the focus position. The comparative analysis of the photographic images and the characteristics of the simultaneously recorded ultrasonic signals shows that the amplitudes and the arrival times of the ultrasonic waves can reliably describe the characteristics of the breakdown and its position relative to the water surface. At certain focus positions the existence of double breakdown is evident.