Fourier transform phase shift cavity ring down spectroscopy

The spin-forbidden b1Σg+(v′=0)←X3Σg−(v″=0) band of molecular oxygen in air has been measured to show that broad band continuous wave phase shift cavity ring down spectroscopy can be combined with Fourier transform spectroscopy. In contrast to ordinary cavity ring down spectroscopy, where a laser is used to excite the ring down cavity, here, an incoherent continuous broad band light source is used. This opens the way to build a Fourier transform spectrometer with which absorption measurements can be performed at a resolution determined by the Michelson interferometer and over a wavelength range from 10 μm to 250 nm with a sensitivity increase of about three orders of magnitude, as compared to standard Fourier transform spectrometers.