Dispersed rayleigh interferometer

In order to further improve the performance of Rayleigh Interferometer (RI) used for measurement of gas/liquid index, a Dispersed Rayleigh Interferometer (DRI), which uses a broadband source and disperses monochromatic interference pattern perpendicular to the direction of baseline, is proposed to expand measurement range and to acquire optical path difference dynamically by only one frame of interference pattern. At the same time, an algorithm used to analyse the interference pattern automatically is proposed. A DRI which uses a pair of transmissive phase plates used for generating optical path difference has been built up. The measurement range reaches 200ìm, measurement error is less than 20nm and repeatability is better than 2nm in whole range. Good performance of DRI makes itself to be a suitable approach not only used in the conventional measurement of gas/quid index, but also in other aspects, for example, co-phasing of segmented mirrors for large telescopes.