IMAGING SURFACE-WAVE ANALYZER FOR LIQUID SURFACES

We have developed a wave-height sensor that can be used to measure sur face height directly and simultaneously over a two-dimensional imaged area of an air-liquid interface, thus permitting real-time two-dimensi onal wave-height spectra to be obtained directly by fast Fourier trans form. The absolute interface height (or surface-wave amplitude) is obt ained directly from the measured volume attenuation of the transmitted Light through the medium rather than by tedious reconstruction from s urface slope data obtained by light refraction or reflection methods. A surface-height resolution of tens of micrometers has been achieved. For this demonstration, two-dimensional gray-scale wave-height images of cylindrical surface waves are presented with corresponding two-dime nsional fast Fourier transforms. Line scans across the images indicate the ready utility of the instrument to obtain surface-height informat ion at any location on the imaged area. Applications of this diagnosti c and design issues of a two-dimensional wave-height spectrum analyzer are presented. (C) 1997 Optical Society of America.