Cavity-ringdown molecular spectroscopy based on an optical frequency comb at 1.45-1.65 μm

Optical frequency comb-based cavity-ringdown spectroscopy has recently enabled high-sensitivity absorption detection of molecules over a broad spectral range. We demonstrate an improved system based on a mode-locked erbium-doped fiber laser source centered at 1.5 mu m, resulting in a spectrometer that is inexpensive, simple, and robust. It provides a very large spectral bandwidth (1.45 - 1.65 mu m) for investigation of a wide variety of molecular absorptions. Strong molecular absorptions at 1.5 urn allow for detection at sensitivities approaching the 1 part in 10(9) volume level. We provide a detailed description of our spectrometer and present measurements of the rovibrational spectra for CO, NH3, and C2H2 with an absorption sensitivity of 2 X 10(-8) cm(-1) Hz(-1/2) per detection channel. (c) 2007 Optical Society of America.