Knowledge Bank

Interferometric modulation is a technique for obtaining spectral information in the far-infrared region of the spectrum, where detector noise limits the resolution that tan be obtained with diffraction gratings. The observations consist of obtaining a plot of the illumination resulting from the interference of two coherent beams of radiation as a function at their path difference. The transformation from observed data to spectra is discussed, and the scanning’‘ function for an interferometric modulator, similar to the diffraction grating scanning’‘ function, is arrived at. The resolving power to be expected from this interferometric technique is shown to be proportional to the maximum path difference between the interfering beams, the lamellar-grating type interferometer and auxiliary apparatus is described. Far-infrared spectra, obtained with the instrument, $indicating=(1/4]cm-1$ resolution, are presented.