|Smoke and Mirrors: Ultra-Rapid-Scan FT-IR
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 Dybwads 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.