Study of optical-acoustical phenomena at surface of strongly absorbing clearing fluids

The clearing of water by laser radiation with a wavelength lambda = 2.94 microns was reported by K. L. Vodop'aynov, et al., (ZhETF, Vol. 82, p 1820, 1982). For further clarification of this problem, the authors studied optical-acoustic phenomena at the surface of a fluid under conditions of strong absorption and optical clearing with emphasis on detection of the characteristics of the thermal and evaporation regimes of generation of acoustic fields by laser radiation. Studies were made of different fluids containing hydroxyl groups (water, ethanol, glycerin, ethylene glycol) with different boundary conditions (free and fixed boundaries). In the case of a free boundary, the laser radiation was directed downward along the normal to the fluid surface, but in the case of a rigid boundary the fluid surface was covered by a backing of transparent material. Experimental results are presented. At the present time there is no certain interpretation of the observed effects. However, it is known that the presence of hydrogen bonds in fluids containing the OH group leads to a strong shift into the region of lesser frequencies of the absorption band. Partial breaking of the hydrogen bonds under the influence of laser radiation can result in a change in the absorption spectrum of the fluid and accordingly a clearing at the laser wavelength.