Massively-parallel intracavity trace molecular detection in the mid-infrared using broadband frequency combs

摘要

Ultrasensitive detection of methane, isotopic carbon dioxide, carbon monoxide, formaldehyde, acetylene and ethylene is performed in the spectral range 2.5 - 5 μm using intracavity spectroscopy inside a broadband optical parametric oscillator (OPO). The two separate OPOs were operated near degeneracy and were synchronously pumped either by a mode-locked erbium (1560 nm) or thulium (2050 nm) fiber laser. A large instantaneous bandwidth of up to 800 cm~(-1) allowed for simultaneous detection of several gases. We observed an effective path length enhancement due to coherent interaction inside the OPO cavity and achieve part-per-billion sensitivity levels.