Nanosecond resolution photography system for laser-induced cavitation based on PIV dual-head laser and industrial camera.

The detailed study of the initial and collapse processes of the laser-induced cavitation requires nanosecond resolution (both nanoseconds exposure and nanoseconds interframe time) of the photography measurement system. The high-speed video cameras are difficult to achieve nanoseconds interval time. The framing and streak cameras are able to reach the nanosecond resolution, but their complex technology and expensive prices make them far from being commercially available. The present study builds a nanosecond resolution photography system based on PIV dual-head laser and conventional industrial camera. The exposure time of the photography system is controlled by the laser pulse width, which is 5 ns. The two heads of the PIV laser are operated independently thus the smallest time interval between two laser pulses can be set to less than 10 ns. A double-pulse per-exposure imaging technique is used to record the information from two laser pulses on single frame on a low-speed industrial camera. The nanosecond resolution photography system was applied to the laser-induced cavitation experiments to verify the reliability of the measurement results. The measurement of the shock wave velocity demonstrates the ability of the system to capture ultrafast phenomena, which reduces from 3611 m/s to approximately 1483 m/s within 400 ns. The experimental results also reveal the asymmetric evolution of laser-induced cavitation bubbles. The major axis of the ellipsoidal bubble has twice reversals along the laser propagation and perpendicular direction from the laser-induced breakdown to the first collapse.