Nonlinear Laser-Induced Deformations of Liquid-Liquid Interfaces: an Optical Fiber Model
Experimentally, it turns out that radiation forces from a cw-laser on a liquid-liquid interface are able to produce giant deformations (up to about 100μm), if the system is close to the critical point where the surface tension becomes small. We present a new model for such a fingerlike deformation, implying that the system is described as an optical fiber. One reason for introducing such a model is that the refractive index difference in modern experiments, such as those of the Bordeaux group, is small, of the same order as in practical fibers in optics. It is natural therefore, to adopt the hybrid HE_{11} mode, known from fiber theory, as the fundamental mode for the liquid system. We show how the balance between hydrodynamical and radiation forces leads to a stable equilibrium point for the liquid column. Also, we calculate the narrowing of the column radius as the depth increases. Comparison with experimental results of the Bordeaux group yields quite satisfactory agreement as regards the column width.