Laser-induced cavitation and explosive boiling in superheated liquids: a new GHz probe

Abstract

Sub- and microsecond relaxation dynamics of superheated surface layers of bulk water cavitating at near-spinodal conditions during heating sub-microsecond long TEA CO2 laser pulses were studied using contact broad-band photoacoustic spectroscopy. Characteristic nanosecond pressure-tension cycles representing steam bubble oscillations were recorded by an acoustic transducer and corresponding oscillation frequencies were measured as a function of incident instantaneous laser fluence during the heating laser pulses. Fundamental oscillation frequencies-9-11 MHz-were found to remain nearly constant in a broad laser fluence range, corresponding to bubble diameters close to thickness of the superheated surface layers. Damped nanosecond and microsecond oscillatory pressure-tension cycles recorded by an acoustic transducer are related to oscillations of steam bubbles of different sizes exhibiting strong dissipative losses and collective (coalescence and percolation) phenomena. These observations demonstrate the apparent ultimate thermodynamic limit of superheating for bulk liquids near their liquid-vapor spinode curves and provide an important insight into basic thermodynamic parameters and spatiotemporal scales of explosive liquid/vapor transformations in absorbing fluids ablated by short laser pulses in the thermal confinement regime.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.