Fourier Transform Infrared Phase Shift Cavity Ring Down Spectrometer

"OPTRA proposes a Fourier transform phase shift cavity ring down spectroscopy (FT-PS-CRDS) system for high sensitivity detection of air toxic compounds. Our system operates in the 400-4000 cm-1 spectral range wherein lie vapor phase resonance bands for most air toxic compounds and hazardous chemicals; the spectral resolution is 4-16 cm-1, depending on the discrimination requirements. Our approach differs from previous FT-PS-CRDS systems as we have eliminated the external modulator and lock-in detection electronics. Historically, these systems measure a phase delay incurred by light traversing a resonant cavity; the phase delay is proportion to the product of the ring down time and modulation frequency. Instead we measure the spectrally dependent phase delay of the modulation frequencies imposed by the interferometer itself. Our approach is simpler than previous FT-PS-CRDS systems and represents a significant cost reduction without the external modulator. In addition this approach produces the entire FT-PS-CRDS spectra in a single rapid scan, making the technique truly real time and significantly faster than previous techniques. Based on radiometric projections, our FT-PS-CRDS system will be capable of ppb detection limits with an integration time of 1 second. Under the Phase I effort, we will design, build, and test a breadboard FT-PS-CRDS system operating in the 700-1400 cm-1 spectral range to establish the feasibility of the proposed approach. Phase II plans will include the extension of the spectral range and the development of a full scale prototype. The Phase II will also address automated multicomponent algorithms. Potential commercial applications include high sensitivity detection of air toxic compounds, chemical warfare agents, and other hazardous chemical, industrial monitoring, and environmental sensing. "