Optical Breakdown In Liquid Research Articles

Condensation of laser‐produced gold plasma during expansion and cooling in a water environment

Physical processes involved in laser ablation in liquid (LAL) are studied using a gold target irradiated through transparent water. During and after irradiation, the heated material from the surface of a target produces a plume that expands into liquid‐forming nanoparticles (NPs). The LAL method of NP production is ecologically much cleaner than others. A better understanding of the processes associated with complicated hydrodynamic phenomena leading to LAL is important for controlled manufacturing. We consider laser pulses with different durations τL covering fifth orders of magnitudes ranging from 0.1 ps to 0.5 ns and large absorbed fluences Fabs near optical breakdown of liquid. It is shown that the trajectory of the contact boundary with liquid at the middle and late stages after passing the maximum intensity of the longest pulse is rather similar for very different pulse durations if energies Fabs are comparable. We trace how hot (in a few eV range) dense gold plasma expands, cools down, intersects a saturation curve, and condenses into NPs appearing first inside the water‐gold diffusively mixed intermediate layer where gold vapour has the lowest temperature. Later, the pressure around the gold‐water contact drops down below the critical pressure for water. As a result, the nanoparticles find themselves in gaseous water bubble where density of water gradually decreases to 10−4 − 10−5 g/cm3 at maximum bubble expansion.

Specific features of the acoustic emission upon the optical breakdown in liquid induced by the radiation of Nd:YAG laser

The acoustic emission from the zone of the optical breakdown in liquid is experimentally studied. The spectral characteristics and energy of the acoustic wave that is generated in liquid due to expansion of the plasma formation initiated by the optical breakdown at a wavelength of 532 nm are analyzed. Two spectral peaks that characterize the acoustic emission and the low-frequency shift of the low-frequency peak owing to an increase in the laser pulse energy are demonstrated. In general, the linear dependence of the acoustic pressure on the laser pulse energy is observed. The acoustic data can be used to reconstruct function R(t) that is in agreement with dependences R(t) resulting from the optical data. This circumstance is important for the study of breakdown in opaque media.

液体中光击穿所激发声场的理论研究

The sound field excited by laser-induced liquid breakdown is studied using fundamental theories of acoustics.Based on plasma ellipsoid model,a plasma elliptical disk model is proposed to simplify the processing and theoretical calculations.Via putting forward the plasma elliptical dish model,the law of sound pressure and a plasma elliptical dish vibration analytical expression of displacement are obtained,which provide certain theoretical basis to optical breakdown in liquid.

Influence of dissolved gas on optical breakdown and small-angle scattering of light in liquids

It is demonstrated that the small-angle laser beam scattering pattern in liquid depends greatly on the dissolved gas content: the intensity of the scattering steeply drops after degassing doubly distilled water. It was experimentally found that the parameters or small-angle scattering of light correlate strongly with those of optical breakdown in liquid. Namely, the fractal dimension and the gyration radius of scatterers in aqueous KCl solutions behave similar to the optical breakdown probability in those liquids versus salt concentration, while the optical breakdown cannot be induced after degassing. The effect might be associated with the presence of stable gas microbubbles in liquid.