Image for: Instantaneous trace gas fingerprint with laser frequency combs

A high-finesse cavity, in which all the resonant equidistant modes of a laser frequency comb are simultaneously injected, produces a dramatic increase of the interaction length of the light-field and intracavity-matter. The resulting ultrasensitive broad-spectral-bandwidth transmission spectrum is measured in real-time with another comb. This picture represents a part of the high-finesse passive resonator similar to the one that has been used to enhance the sensitivity of frequency comb based Fourier transform spectroscopy. The green light coupled to the resonator comes from a frequency-doubled Ytterbium-doped fiber frequency comb. While the letter (doi:10.1038/ nphoton.2009.217) published in Nature Photonics reports spectroscopic results around the fundamental infrared 1040-nm wavelength of the Ytterbium femtosecond lasers, the implementation of the same kind of experiments around the Yb-laser second harmonic, where interesting rovibronic molecular transitions are lying, is underway.