EFFECTS OF THE SELF-EMISSION OF AN IR FOURIER-TRANSFORM SPECTROMETER ON MEASURED ABSORPTION-SPECTRA

Up to now the effect of the modulated thermal self-emission of Fourier -transform spectrometers has been investigated for emission measuremen ts only. But this instrumental radiation also influences Fourier-trans form absorption spectroscopy in the mid-IR when the Moon, a hot blackb ody, or even the Sun is taken as a radiation source, e.g., by causing small negative radiance values in the center of saturated absorption l ines. For our experimental investigations, a blackbody that can be coo led down to liquid-nitrogen temperature was constructed. Measurements at different temperatures of the blackbody and for different optical c onfigurations in the detector port of the Fourier spectrometer as well as transmission measurements of gas cells are used to examine the sta tements above. (C) 1996 Optical Society of America