Selective modulation in submillimeter spectrometers

The characteristics of the method of internal interference modulation of radiation in two-beam interferometers with dispersion elements are studied. It is shown that it is possible to construct on the basis of this method a selective spectrometer for the submillimeter range with high transmission, high resolution, and synchronous detection. Internal modulation of radiation in a Michelson interferometer with diffraction gratings brings about the recording of the spectrum by matched rotation of the diffraction gratings, leading to change of the tuned interferometer wavelength. An experimental model on this principle was built, and a sample interferogram of the apparatus function and spectrogram of the absorption of submillimeter radiation by atmospheric water vapor are shown.