Scanning Mirror For A Spiraling Toroidal Spectrointerferometer

This paper discusses the generation of a scan mirror -- a critical component in a novel Fourier transform spectrometer that is being developed at the Naval Weapons Center. The instrument is a double-beam interferometer that uses rotational motion to change path length. The major component in this interferometer is a scan mirror that is locally spherical but has a continually changing (spiraling) radius. When the mirror is rotated around the axis of the spiral, the path length of one of the interferometer beams is changed. Since this interferometer uses rotational instead of linear motion to change the path difference, very accurate alignment during scanning is possible as well as higher scan speeds. The major drawback is that the scan mirror cannot be made by conventional optics fabrication techniques. The theory and design of the interferometer and scan mirror are discussed. The design details of the machine producing the scan mirror, the actual mirror fabrication, and the preliminary surface evaluation and test of a scan mirror are also discussed.