Measurements of the high pressure ultrasonic wave and the cavitation bubble by optodynamic method

Laser induced breakdown in water represents an abrupt high intensity photoacoustic phenomenon. The pressure front that appears at its site represents an ultrasonic shock wave spreading into surrounding water. At the same time the cavitation bubble develops. The effect of both is particularly important in ocular microsurgery, where Q-switched lasers are used to vaporize the tissue in procedures such as posterior capsulotomy. Formation of the cavitation bubble and the propagation of the sound wave were analyzed by an optodynamic experimental set-up. It is based on two-dimensional scanning technique using a beam deflection probe. From the beam deflection probe signals the time of flights for both the sound wave and the cavitation bubble were determined. By using Hugoniot curves and the two-dimensional time of flight data field the pressure amplitude in the front was estimated. Simultaneously the expansion of the cavitation bubble was also analyzed and its energy was determined.