Two schemes for trace detection using cavity ringdown spectroscopy

We describe and compare two schemes of high-sensitivity cavity ringdown spectroscopy (CRDS), both functioning with telecom diode lasers. The first (cw-CRDS) gives high spectral resolution, which is useful for low-pressure trace detection or for laboratory spectroscopy applications. We present a compact prototype partly based on fiber technology. The second scheme exploits optical feedback (of-CRDS) and results in a much simpler setup, more appropriate for realizing low-cost trace-detection devices. PACS 42.62.Fi; 87.64.Ni; 42.68.Ca; 82.80.Gk