Optical Effect On Liquid Surface And Its Application

Compared with the bulk, the liquid surface has much difference in composition, structure, force, energy state, and so on. It is the difference that makes the liquid surface take on some characteristics. One can obtain some parameters of liquid by means of researching them.Optical method is an important technique to detect the substance properties. Of course, this method is a good choice for the surface research as well. When the optical effects, including diffraction, reflection, refraction, occur on the liquid surface, many fantastic phenomena will emerge, which may be used to measure some parameters of liquid, such as surface tension, contact angle, refraction index, consistence, and so on. Therefore, optical methods have been adopted extensively in many fields, for example, Fluid Mechanics, Ocean Optics.In this thesis, we studied liquid surface using optical methods: When a capillary wave propagating along the air-liquid interface, a grating will form on the surface under certain condition. When a collimated-beam illuminated upon the liquid surface, diffraction patterns may be observed. Based on the relationship between the distribution of diffraction intensity and the surface wave, we can study the liquid properties. On the other hand, we also investigated the static liquid surface. In principle, the distribution of the reflection or refraction intensity relates to the shapes of the liquid surface, so the liquid properties can be studied by means of analyzing the distribution. In our research, the major phenomena and conclusions were obtained as follows:1. The high visibility diffraction patterns were observed experimentally in the case of the Low-Frequency Liquid Surface Acoustic Wave (LFLSAW). Furthermore, the disappearance of zero-order diffraction was obtained, which was corresponding to the 100% diffraction efficiency. The phenomena were explained very well using the theory of Fourier Optics.2. When a light beam illuminated upon the static liquid surface, a dark ring appeared on the surface, which was named the Effect of Light-Obstructed in the thesis. The mechanism of the phenomenon was discussed using the theory of Geometrical Optics. In addition, the relationship between the radius of dark ring and the refraction index of liquid was derived. Based on the discovery and our analysis, a new method was established to measure the refraction index of transparence liquid.illFurthermore, owing to the quantitative correspondence relationship between the consistence and its refraction index, the consistence of solution was also measured by this method.3. When a needle was inserted into a liquid, a symmetric meniscus appeared around the needle, that is to say, a local-curved surface formed on the liquid surface, which was caused by the effect of the liquid wetting the needle. An ellipse-shape dark area or a star-shape bright area was formed on the observation plane, when a collimated-beam illuminated upon the symmetric meniscus surface. The phenomena were explained using the critical reflection on the local-curved liquid surface. The approximate curve of the symmetric meniscus was obtained by means of the numerical integrating the Young-Laplace Equation.