The Asymmetry Of Diffraction Patterns From Liquid Surface Waves And The Critical Light Reflection From The Curved Liquid Surface

The surface wave is a kind of elastic wave which travels along the substance (liquid or solid) surface. It acts as an important method to detect the characteristic of substance, which was recognized very early and applied widely. How to detect the physical properties of the surface and internal of the substance with use of surface wave, one always make his best to do this field. But until 60's, the development of the laser technology has provided the essential technology for the optical visualization of the surface wave. But most of them were performed for the waves on the solid surfaces. For the research of the liquid surface wave, due to the complicated physical properties on the interface between the fluid and gas, few researches were performed. In 1979, GWeisbuck realized the light diffraction by the liquid surface wave, which has established the measurement of the surface tension by the optical method. How to get the surface and internal properties of the liquid in a rapid way, which plays an important role in our daily life, such as in the Petroleum mining, Dye chemical industry and so on.Optical method is an important technique to detect the substance properties. By studying the optical effects, such as diffraction, reflection and refraction, occurring on the liquid surface, some parameters of the liquid can be measured. And the method was widely adopted in many fields, for example, fluid mechanics, ocean optics. In this thesis, we apply the optical method to study the dynamic liquid surface and static surface. In the dynamic surface research, the surface tension and the surface parameters can be gotten by studying the diffraction patterns from the liquid surface. And we can study the static curved liquid surface by means of the optical method, such as the wetting effect, surface tension and the optical transmission of the curved liquid surface and so on.In our research, the major phenomena and conclusions were obtained as follows:1) Not only the high visibility diffraction patterns were observed experimentally in the case of the Low-Frequency Liquid Surface Acoustic Wave (LFLSAW), but also the asymmetry distribution of the diffraction pattern was observed in our experiment. And the experiment can be repeated very well. Theoretically the approximate conditions of the surface wave diffraction were analyzed, and the corresponding analytic expressionof angle width of diffraction patterns was derived, which explained the asymmetry distribution well.2) Due to the wetting effect, when a needle was inserted into a liquid, a symmetric meniscus appeared around the needle. It is a great interesting to observe and study the liquid surface since few research has been performed. A rounded dark area formed on the observation plane, when a collimated-beam illuminated upon the symmetric meniscus surface in a vertical direction. And the diameter of the dark area will change with the diameter of the laser beam. The non-uniform distribution of intensity was observed around the boundary of the dark area. The phenomena were explained using the critical reflection on the local-curved liquid surface. The relation between the height of the curved liquid surface and the distance was obtained, and the theory and experiment results are in good agreement.