|Smoke and Mirrors: Ultra-Rapid-Scan FT-IR
The reason that ranges of modulation frequencies were quoted is that
retardation and optical velocity in this interferometer, and in most completely rotating
designs, are sinusoidal functions of time. There is then a fundamental tradeoff between
duty cycle and velocity variation. A duty cycle efficiency of 66% was chosen, which
corresponds to a factor of two variation in velocity. The extremes of retardation must be
slightly larger than desired range of operation according to the duty cycle. At 90% duty
cycle the velocity varies by a factor of 4.5 from the middle of the scan to the end.