Phase determination from mostly one-sided interferograms

We show how to detect and correct for nonlinear phase shifts in a mainly one-sided interferogram of an emission-line source. We simultaneously detect and correct for an out-of-phase emission background from the spectrometer. The method requires two auxiliary spectra, one of a strong continuum source, and one of an emission-line source with little or no continuum. Key words: Fourier transform spectroscopy, interferometer, phase.