Optical Soppler imaging with field-widened Michelson interferometers

Abstract

In a field widened interferometer, the optical path difference changes by less than one wavelength over a field of view of ten degrees or more, making it particularly suitable for imaging. The Wide Angle Michelson Interferometer (WAMI) is a conceptually simple device, constructed for a single path difference, that generates a cosinusoidal output whose phase yields the Doppler velocity, and whose modulation depth gives the temperature. In practice, such a field widened configuration involves refractive material, but by careful selection the assembly can be compensated for thermal and wavelength variations of the glass constants. In this mode the WAMI provides an extremely efficient way of extracting Doppler information from a simple known spectrum, such as an isolated Gaussian line, or even a doublet. However, when additional spectral information is required, it is necessary to combine the WAMI with a low resolution Fabry-Perot etalon. Two spaceflight imaging WAMIs now under construction are described; the space shuttle WAMDII, and WINDII, which will fly on the Upper Atmosphere Research Satellite.