Frequency-modulation Fourier transform spectroscopy: a broadband method for measuring weak absorptions and dispersions.

A new method, FM-FTS, combining frequency modulation heterodyne laser spectroscopy and Fourier transform spectroscopy is presented. It provides simultaneous sensitive measurement of absorption and dispersion profiles with broadband spectral coverage capabilities. Experimental demonstration of the overtone spectrum of C(2)H(2) in the 1.5 microm region is presented.