Distortion free interferograms in Fourier transform spectroscopy with nonlinear detectors.

A new method for removing the most important distortions from Fourier transform spectra recorded with nonlinear detectors is reported and illustrated with practical examples. The removal of these distortions is obtained with a two-output interferometer configuration. This essentially works because the resulting interferogram is made up of the difference between the signals of the two detectors and because these signals have the same amplitude and opposite phases. The proposed method leaves the detectors unchanged and makes use of their distorted signals. The correction is not restricted to the nonlinear effects of the only detectors but also of the entire electronic system amplifying each detector signal. It easily applies to absorption, emission, low and high resolution spectra, as well as spectra of short and long lifetime phenomena. The benefit of the method is not restricted to Fourier transform spectroscopy. It is even not restricted to techniques making use of detectors. Its advantages are available for any data treatment where the important information is made up of the difference between nonlinear functions (or signals) having similar amplitudes and opposite phases, whatever the number of pairs of such distorted functions (or signals) may be.