Opto-Acoustic Effects by Laser Breakdown of Seawater in an Ultrasonic Field

Abstract

Studies of the opto-acoustic effects accompanying laser breakdown in water generated by focused laser and ultrasonic radiation are performed. For the first time, the experimental results were obtained showing sharply increasing effects of acoustic emission from the breakdown zone under the combined influence of laser and ultrasonic irradiation. Experiments were performed using the nanosecond pulses of a Nd:YAG laser operating at a wavelength of 532 nm. Acoustic radiation was generated by acoustic focusing systems at various frequencies. It is shown that recording of acoustic emission from the breakdown zone makes it possible to study the thresholds and dynamics of the laser breakdown, which coincide with the high-speed optical methods. The results obtained make it possible to find applications of the acoustic method of diagnostics of laser breakdown and cavitation in opaque environments for which optical methods are not applicable. The effect of the increase in the resolution of the spectral lines of chemical elements in seawater under the action of an ultrasonic field is established. This effect indicates the possibility of development of a combined method of laser–spark spectroscopy using ultrasound, which will make it possible to approach the sensitivity of the precision chemical analysis, and which should be more practical and advanced because it yields a high efficiency and detailed measurements.