Fourier transform spectroscopy with a laser frequency comb

Molecular fingerprinting using absorption spectroscopy is a powerful analytical method, particularly in the infrared, the region of intense spectral signatures. Fourier transform spectroscopy-the widely used and essential tool for broadband spectroscopy-enables the recording of multi-octave-spanning spectra, exhibiting 100 MHz resolution with an accuracy of 1 x 10-(9) and 1 x 10(-2) in wavenumber and intensity determination, respectively. Typically, 1 x 10(6) independent spectral elements may be measured simultaneously within a few hours, with only average sensitivity. Here, we show that by using laser frequency combs as the light source of Fourier transform spectroscopy it is possible to record well-resolved broadband absorption and dispersion spectra in a single experiment, from the beating signatures of neighbouring comb lines in the interferogram. The sensitivity is thus expected to increase by several orders of magnitude. Experimental proof of principle is here carried out on the 1.5-mu m overtone bands of acetylene, spanning 80 nm with a resolution of 1.5 GHz. Consequently, without any optical modi. cation, the performance of Fourier spectrometers may be drastically boosted.