The source of a problem with rapid-scanning fourier transform spectroscopy

In this paper, a difficulty with rapid-scanning interferometers will be discussed. By “rapid-scanning interferometer” is meant one which uses no chopper or lock-in amplifier in the data-acquisition system. Instead, the moving mirror is scanned at a constant velocity, making the infrared intensity at the detector be modulated in the audio frequency range. The signal from the detector is amplified by a broadband amplifier and digitized for later processing by a computer. This technique has advantages over the “step and integrate” procedure insofar as simplicity of interferometer drive, noise reduction, and suppression of long-term drifts in source or detector are concerned.