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

We describe a method for the direct, absolute and noninvasive measurement of surface height profiles on air-liquid interfaces. Wave amplitude spectra are directly obtained from electronically imaged surface height profiles without resorting to problematic reconstructions from wave 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 of micrometers has been demonstrated. A suitable photodiode detector and an appropriate laser provide the two parameters which are sufficient to optimize system spatial and temporal resolution and spatial dynamic range.