In the past fifteen years, sample modulation infrared spectroscopy has been introduced for the analysis of dynamic processes. Sample modulation measurements were initially restricted to a few custom-built dispersive instruments, but the recent introduction of commercial step-scan Fourier transform infrared (FT-IR) spectrometers has made dynamic infrared spectrometry widely practical.
Boiana O. Budevska, Christopher J. Manning, and Peter R. Griffiths, "Comparison of Two-Dimensional Power and Phase Spectra Generated from Sample Modulation Step-Scan FT-IR Experiments," Appl. Spectrosc. 48, 1556-1559 (1994)