Asymmetric optical radiation pressure effects on liquid interfaces under intense illumination

Deformations of horizontal liquid interfaces by optical radiation pressure are generally expected to display similar behavior, whatever the direction of propagation of the exciting laser beam is. We found that this expectation is borne out as long as the cw laser illumination is moderate in strength. However, we found that, as a striking contrast for high field strengths, either a large stable tether can be formed or a breakup of the interface can occur, depending on whether the laser beam is directed upward or downward. Physically, the reason for this asymmetry can be traced to whether total reflection can occur. We present two simple theoretical models, one based on geometrical optics, the other on wave optics, that are able to illustrate the essence of the effect. In the case leading to interface disruption our experimental results are compared with those obtained by Zhang and Chang for water droplets illuminated by intense laser pulses [Opt. Lett. 13, 916 (1988)]. A key point in our experimental investigations is to work with a near-critical liquid-liquid interface. The surface tension therefore becomes significantly reduced, which thus enhances the magnitude of the stationary deformations induced. (C) 2003 Optical Society of America.