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BB-DEFCOM-CRDS
Recently, we have initiated the development of a new technique, firstly introduced by Chandler et al [1] and called Dual Etalon Frequency Comb Cavity Ring-Down Spectrometer, but extended to broadband (BB) laser sources. The principle consist in generating two slightly different frequency combs out of two high finesse optical cavities of similar but not equal lengths. Heterodyning is then used to measure the beat notes thanks to the Fourier Transform (FT) analysis of the signal from the heterodyne receiver. These beating are characterized by heterodyne peaks separated in frequency by values corresponding to the difference of the Free Spectral Range of the 2 cavities. The time-resolved FT analysis allows to measure the decay time, as in conventional CRDS, for all beat notes. This technique should allow performing absorption spectroscopy with a much better spectral resolution (several hundredths of kHz) than using our conventional light sources (nanoseconds pulsed lasers).
[1] Dual Etalon Frequency COMb Cavity Ring-Down Spectrometer, David.W. Chandler, Kevin E. Strecker, J. Chem. Phys. 136, 154201, (2012), doi : 10.1063/1.3700473