Fourier-transform cavity-enhanced absorption spectroscopy using an incoherent broadband light source

A cavity-enhanced absorption setup employing an incoherent broadband fight source was used in combination with a Fourier-transform spectrometer to measure the spin-forbidden B-band of gaseous oxygen at -688 nm and several weak absorption transitions of water vapor in the same spectral region at room temperature in ambient air. The experiments demonstrate that the sensitivity of a Fourier-transform spectrometer can be significantly improved by increasing the effective path length, while retaining a rather small sample volume. In comparison with a single-pass absorption measurement, we report a path-length enhancement factor of 200 and an improvement of the signal-to-noise ratio of ≈6 in the present cavity-enhanced absorption experiment. The practical advantages and limitations of this novel approach are outlined and potential applications are briefly discussed.