Optical and Acoustic Study of Nucleation and Growth of Bubbles at a Liquid-Solid Interface Induced by Nanosecond-Pulsed-Laser Heating

The dynamics of liquid-vapor phase-change in the nanosecond time-scale induced by pulsed-laser heating of a liquid on a solid sample is studied by means of optical reflectance and scattering measurements, and the piezoelectric detection technique. The Iiquids studied include water, ethanol, merhanol, EsopmPmpyl Alcohol P A ) , and mixtures of water and IPA. The threshold fluence for nucleation is determined with high accuracy using the optical and acoustic signals. Heat diffusion calculations performed for the threshol$ fluences indicate that the Iiquids are sufficiently superheated before nucleation sets on. The transient optical reflectance signal is analyzed by an effective-medium theory to provide bubble-growth kinetics, so that Phe bubble-growth velocity for the test liquids could lx estimated. In addition, it is observed that, following the thermally induced nucleation, repetitive acoustic cavitation at the surface of the solid sample occurs, with a time interval related to the speed of sound in the liquid. PACS: 64.70.Fx, 79.20.D~ The science of the metastability behavior of superheated pure or mixed Iiquids is well established only in the nearsteady-state regime with a time scale of microseconds or longer [1-4]. In the much faster repme with a time-scale of nanoseconds, superheated liquids may have different behavior, including lhe limit of the superheat, bubble nucleation and growth lunetics, and heterogeneous nucleation process at a surface. Such behaviors in the fast regime have not been investigated, because the traditional experimental techniques, such as short-pulsed elecnical-current heating [l] and bubble column apparatus [5], lack speed and sensitivity. Recently, we have used pulsed-laser heating to produce faster superheating of liquids in the nanosecond-time-scale. In pulsed-laser heating the liquid can be heated directly if it is absorptive at the laser wavelength, as has been the approach in the heating of a liquid with the free surface in a container [6], or in the studies of explosive vaporization of aerosol droplets by C02 lasers 57, 81. Alternatively, the liquid can be heated indirectly if it is transparent to the laser wavelength but is in contact with an opaque solid sample which absorbs the laser light. Recently, it was observed that this kind of liquid evaporation can be efficiently used to remove submicron-sized particles from soIid surfaces [9,10]. Due to the practical significance of this "s;team laser cleaning", many physical aspects such as nucleation dynamics, explosion tlmsholds for different Iiquids and substrates, and the pressures generated by the evaporation process need detailed investigation. Various methods including piezoelectric detection [ I I], optical transmission probe [12,13], and probe-beam deflection [I41 have been applied previously to the studies of these phenomena with some experimental re-