Broad spectral bandwidth frequency-modulation spectroscopy

In this paper, we report a new spectroscopic method offering sensitivity, resolution, and broad spectral bandwidth based on high frequency modulation. The experiment makes use of a Fourier transform (FT) spectrometer. One of the main advantages of FT Spectroscopy is its experimental ability to record at once extended spectral ranges and to give easy access to the infrared domain. To achieve high sensitivity, a new way of modulating the interferogram is presented. The key concept is that the modulation is performed at radio frequencies. Both the absorption and the dispersion associated with the spectral feature can be measured simultaneously. Since the measured signals have little noise at radio frequencies, detection can be performed with a high degree of sensitivity. Illustration is provided with different light sources.