In a conventional FT-IR spectrometer operating with an optical velocity appropriate for a pyroelectric detector, at 4 cm^-1 resolution, the time required for one scan is approximately 840 ms. An MCT detector produces better results with a substantially higher optical velocity, but the scan time is still about 42 times longer than the target of 1 millisecond. If a 4 cm^-1 interferogram is scanned at constant velocity in 1 millisecond, the reference laser will be modulated at 4 MHz and mid-infrared radiation will be modulated at frequencies between 100 kHz and 1 MHz. The mirror velocity under these conditions would be 250 cm/s.