Heterodyne method for refractometric measurement and stabilisation of wavelength

摘要

A description is given of a heterodyne interferometric method for measuring the refractive index of the air or of another medium using a two-chamber refractometer and a radiation source allocated to each. The mechanical chamber lengths of the vacuum chamber as reference and of the measuring chamber in free air are equal and constant relative to each other. In both chambers, the number of interferences is held constant over the chamber length by controlling the frequency of the radiation source allocated to the measuring chamber. The frequencies of both radiation sources are brought into interference and the beat frequency is measured. The ratio of the beat frequency to the carrier frequency is the measure of the refractive index. In terms of instrument construction, the method is very simple and of high resolution and can be used for stabilising both the wavelength and the frequency. <IMAGE>