REAL-TIME WAVE-AMPLITUDE SPECTRUM ANALYZER FOR AIR-LIQUID INTERFACES

We describe a method for the direct, absolute and noninvasive measurem ent of surface height profiles on air-liquid interfaces. Wave amplitud e spectra are directly obtained from electronically imaged surface hei ght profiles without resorting to problematic reconstructions from wav e slope measurements. This measurement principle relies on the volume attenuation of light in the liquid rather than the refraction of light at the wave-supporting interface. Surface height resolution of tens o f micrometers has been demonstrated. A suitable photodiode detector an d an appropriate laser provide the two parameters which are sufficient to optimize system spatial and temporal resolution and spatial dynami c range.