Theoretical considerations of laser-induced liquid-liquid interface deformation

• Published in: Physica scripta 2013-05, Vol.87 (5), p.55402-8
• Main Authors: Aanensen, N S, Ellingsen, S Å, Brevik, I
• Format: Article
• Language: English
• Subjects: Deformation; Heating; Lasers; Liquid-liquid interfaces; Liquids; Mathematical analysis; Nonlinearity; Searching
• ISSN: 0031-8949; 1402-4896
• DOI: 10.1088/0031-8949/87/05/055402

In the increasingly active field of optofluidics, a series of experiments involving near-critical two-fluid interfaces have shown a number of interesting nonlinear effects. We here offer, for the first time to our knowledge, an explanation for one such feature, observed in experiments by Casner and Delville (2003 Phys. Rev. Lett. 90 144503), namely the sudden formation of 'shoulder'-like shapes in a laser-induced deformation of the liquid-liquid interface at high laser power. Two candidate explanations are the following. Firstly, the shape can be explained by balancing forces of buoyancy, laser pull and surface tension only, and the observed change of deformation shape is the sudden jump from one solution of the strongly nonlinear governing differential equation to another. Secondly, it might be that the non-trivial shape observed could be the result of temperature gradients due to local absorptive heating of the liquid. We report that a systematic search for solutions of the governing equation in the first case yields no trace of solutions containing such features. By contrast, an investigation of the second option shows that the narrow shape of the tip of the deformation can be explained by a slight heating of the liquids. The local heating amounts to a few kelvins, with the parameters given, although there are uncertainties here. Our investigations suggest that local temperature variations are the crucial elements behind the instability and the shoulder-like deformation.