Abstract

We present an optical frequency comb spectrometer [1] based on an Er:fiber femtosecond laser, operating in the 1.5–1.6 µm range. Comb teeth are locked to the resonances of an enhancement cavity (finesse F= 8500), which extends the effective path length to more than 3 km. Locking of comb lines to the enhancement cavity can be done either by a low-bandwidth (~20Hz) swept locking scheme [2, 3] or a tight, two-point lock [4] with the Pound-Drever-Hall method. Cavity transmission spectrum is resolved by a combination of a high resolution (1 GHz) virtually imaged phase array (VIPA) etalon [3, 5] and a diffraction grating, creating a two dimensional diffraction image, which can be then translated into the absorption spectrum. The optical bandwidth of the detection system equals approx. 30 nm, recording spectra in approx. 15 000 frequency channels simultaneously. The acquired frequency range can be changed by simple grating rotation. The simultaneous bandwidth of the system allows for acquisition of the whole branches spectra of CO and CO₂ in a single measurement.

© 2015 IEEE