The Liquid Optical Breakdown Acoustic Effect

The interaction between laser and liquid can inspire sound waves in liquid, the way which produces sound source is called OA. There are a lot of mechanisms which can inspire sound waves by the interaction of laser and liquid, because of the different energy density in the laser irradiation area, they can be mainly divided into thermal expansion mechanism, gasification mechanism and optical breakdown mechanism, among these, and optical breakdown mechanism has the highest optical conversion efficiency.The waves effect produced by optical breakdown in liquid can be used to monitor chemical process; and be used to research the absorption of optical by chlorophyll and carotene and photosynthesis in biology; be used to study relationship among human, animal hard, soft tissue pathology and spectral, and the measurements of skin and bone, especially the breakdown effect in the eyes arouse the researchers'interest in the field of medicine; can conduct shoals detection, underwater communication, marine geomorphic features and ocean depth measurements, also can be used for measurement of the sound velocity in liquid, sound attenuation and weak optical absorption coefficient in the sea; In recent years, the application of laser in underwater sound, including the application in marine and national defense, always got the attention of people. Traditional sound source must be submerged in water to produce sound waves and source position has certain limitation. Lasers can remotely inspire sound waves, and can be easy to control the position of the optical source. Therefore, optical breakdown technology in liquid has important engineering application background.In this paper, based on plasma column model and plasma target disk model, considering laser pulse features in focus area, using the theory of acoustic base, the plasma ellipsoid model have been proposed, which principle applying to liquid optical breakdown.Via putting forward the plasma ellipsoid model, the directivity of the sound fields excited by laser-induced liquid breakdown is studied through theory by using fundamental theories of acoustics. So a conclusion is drawn that directivity calculated by theory. The directivity of the laser-induced sound field is related to energy range and radiation area of the laser beam.Comparing with the original column model and target disk model, plasma ellipsoid model can describe experimental conditions when the optical breakdown of the whole liquid occur in different energies and irradiation area size, especially laser beam energy is very high and larger irradiation regions of laser are more agreement with experimental conditions. Meantime, it also showed that the theory of plasma column model fits very well with experimental values, when energy of the laser beam is more than threshold optically and irradiation area was small. When energy of the laser beam is larger and irradiation area is larger, the plasma target disk model theory accords with experimental conditions better. In addition, another advantage of plasma ellipsoid model is able to estimate acoustic amplitude (Aij) and sound pressure (Pij) generated by single vibration source according to energy of laser beam and boundary conditions of optical breakdown in the liquid objectively. Through the theoretical analysis of this model, the results describe directivity of sound field produced by the optical breakdown in liquid and have certain directive significance to understand, develop and utilize optical breakdown technology.The sound field excited by laser-induced liquid breakdown is studied by using fundamental theories of acoustics. Based on plasma ellipsoid model, to simplify the processing and theoretical calculations, we proposed plasma elliptical disk model. Via putting forward the Plasma elliptical dish model, we get the law of sound pressure and a plasma elliptical dish vibration analytical expression of displacement, which provides certain theoretical basis to study optical breakdown in liquid.