Dybwad - In spite of the apparent symmetry mismatch, numerous interferometers based on rotation have been proposed and demonstrated. Apparently, none of these designs have been operated at more than 360 scans per second. This slide shows Dybwad’s design, disclosed in US patent 4,654,530, which uses a rotating infrared-transparent prism (28) to generate 4 scans per revolution. The length of the beam paths through the crystal vary with rotation angle. The advantages of this design include very compact layout, inexpensive components, simplicity and the generation of four scans per revolution of the prism. Disadvantages include low duty-cycle efficiency, dispersion, questions about the strength of suitable IR-transparent materials, and impedance of the flat prism spinning in air. Dispersion may be the most serious of these because it distorts the wavenumber-axis of resulting spectra.