Multi-column Liquid Surface Waves Diffraction Theory

Wave movement phenomena are common in nature, and then the surface wave have been known and studied before many years. SAW travels along the medium surface, which carries a large number of surface information. Therefore the research of SAW become more and more important and have been noticed by many scholars. Especially, the laser which was invented in 1960s is used to study SAW immediately. Researchers are favor of the optical means which possess the lossless, no contacted, real-time and prompt characters.This paper has three sections:First, it introduces knowledge of water wave which people in many years ago had seized ,and the detecting ways of liquid surface acoustic wave. The technologies, including scanning laser slope, the imaging detector of capillary waves, laser interference and laser diffraction so on, are described.Second, at the basis of hydrokinetics theory, derives function of SAW and dispersion relation ofliquid. SAW is known as a 1-D sinusoidal grating, the theory of interference and diffraction are papered in detail, the patterns of interference and diffraction is charactered at last.Finally, it introduces superposition theory of general wave, and analyze the diffraction theory of the resultant wave by some waves, guessed the distribution of diffraction patterns. At the same time, the experimental patterns are obtained. The results of experiment and theory are no difference.In my research, the main conclusions were obtained as follows:1. The formula of laser diffraction from one-dimensional SAW in oblique incidence is derived under proper coordinate system. Furthermore, the relation on between distribution direction of diffraction pattern and incidence angle is also achieved. Although strength of each diffraction grade change by Bessel's function, the angleφno longer corresponds to the angleθ. When the direction of incident laser and the propagation direction of SAW are in same plane, it is observed that the diffraction distribution direction is also located in this plane. However, When the direction of incident laser and the propagation direction of SAW are not in same plane, the diffraction distribution direction is not located in the plane with incident light.2. Referring to combined theory of sinusoidal grating, The formula of laser diffraction from "cross-grating" in oblique incidence is derived. At the same time, the experimental patterns are obtained. The results of experiment are as same as the theory.