Abstract

The fundamental (and strongest) ro-vibrational transitions of atmospheric molecules lie in the mid-IR region of the spectrum (the so-called “molecular fingerprint” region). Since trace-gas detection sensitivity scales inversely with line-strength, mid-IR is the best suited spectral region to perform high-sensitivity molecular spectroscopy. With this motivation, we have designed and realized a difference-frequency-generated coherent source, with 3850 − 4540 nm tuning range and TEM₀₀ spatial mode [1]. Phase locking of the near-IR “pump” laser to the “signal” one involved in the non-linear mixing process, through a Ti:sapphire-based optical frequency comb, also gives the generated “idler” radiation narrow linewidth and Cs-standard traceability [2]. The relatively high power of this source (30 mW at 4510 nm), greatly enhanced by a high-finesse Fabry-Perot cavity (F > 11000), enables saturation spectroscopy at pressures even higher than 10 mbar.

© 2011 Optical Society of America