Cavitation Induced by Continuous Wave Lasers

摘要

Laser induced cavitation bubbles in water results from either dielectric breakdown or the fast evaporation due to radiation absorption. The bubbles expand, reach a maximum radius and then supersonically collapse producing a by shock wave. So far, laser induced cavitation has been observed by using short pulsed (femto to nanosecond) lasers. In this report, we observe laser induced cavitation bubbles by using relatively low power (200 mW) cw light sources. A beam from a cw Nd:YAG laser (λ=1.064 μm) is tightly focused on saturated solution of copper nitrate salt. The large absorption coefficient at the illumination wavelength produces large thermal gradients and high peak temperatures leading to the formation of cavitation bubbles near the solution-glass interface. The collapse of the bubbles is so violent that they can be listened without any special device. Cavitation appears at quite regular time escales. The frequency of bubble formation depends on the laser intensity reaching frequencies as high as 4 KHz. We present detailed experimental results on the bubble formation using a phase contrast, light scattering and hydrophones.