CCD camera as a multichannel analyzer for the spectral and azimuthal resolution of Fabry–Pérot fringes

The Fabry–Pérot interferometer is well known for its very favorable combination of high resolution and throughput. However, the radial dispersion of the spectrum makes multichannel detection difficult. Several systems have been devised that physically split the focal plane into annular elements, but these are normally limited to about ten channels while the Fabry–Pérot has potentially a much higher multichannel capability (e.g., the finesse is typically 20–50). In practice these devices have proved to be difficult to make. We have developed a more efficient and versatile technique where the interference pattern is focused onto a CCD array (640×1024 elements). The data can then be transformed to a circular coordinate system and, for example, provide the means of integrating all the information in selected annular ranges (i.e., a multichannel analyzer). The large number of pixels available enables a working finesse of up to 50 to be realized. The technique is particularly valuable for the detection of partial azimuthal fringes.