title: Direct phase-locking of a 8.6-μm quantum cascade laser to a mid-IR optical frequency comb: application to precision spectroscopy of N2O.
abstract: We developed a high-precision spectroscopic system at 8.6 μm based on direct heterodyne detection and phase-locking of a room-temperature quantum-cascade-laser against an harmonic, 250-MHz mid-IR frequency comb obtained by difference-frequency generation. The ∼30  dB signal-to-noise ratio of the detected beat-note together with the achieved closed-loop locking bandwidth of ∼500  kHz allows for a residual integrated phase noise of 0.78 rad (1 Hz-5 MHz), for an ultimate resolution of ∼21  kHz, limited by the measured linewidth of the mid-IR comb. The system was used to perform absolute measurement of line-center frequencies for the rotational components of the ν2 vibrational band of N2O, with a relative precision of 3×10(-10).
authors: Alessio
authors: A
authors: Gambetta
authors: Marco
authors: M
authors: Cassinerio
authors: Nicola
authors: N
authors: Coluccelli
authors: Eugenio
authors: E
authors: Fasci
authors: Antonio
authors: A
authors: Castrillo
authors: Livio
authors: L
authors: Gianfrani
authors: Davide
authors: D
authors: Gatti
authors: Marco
authors: M
authors: Marangoni
authors: Paolo
authors: P
authors: Laporta
authors: Gianluca
authors: G
authors: Galzerano