Measurements of liquid surface fluctuations using a self-mixing solid-state laser

We propose a highly sensitive method for measurements of liquid surface fluctuations with nanometer-order displacement using a self-mixing laser Doppler velocimeter (LDV) comprising a laser-diode-pumped thin-slice solid-state laser and a simple photodiode. In this measurement system, the scattered light from the liquid surface is reinjected into the solid-state laser, and then the laser output from the solid-state laser is modulated by this reinjected laser light. The time dependence of the displacement of liquid surface fluctuations can be obtained from the analysis of the modulated laser output. We describe various measuring methods and the optical system of the self-mixing LDV for real-time measurements of liquid surface fluctuations. Real-time measurement of liquid surface fluctuations can be performed with high amplitude and frequency resolutions by the analysis of the modulated laser output.