title: Fourier transform and Vernier spectroscopy using an optical frequency comb at 3-5.4  μm.
abstract: We present a versatile mid-infrared frequency comb spectroscopy system based on a doubly resonant optical parametric oscillator tunable in the 3-5.4 μm range and two detection methods: a Fourier transform spectrometer (FTS) and a continuous-filtering Vernier spectrometer (CF-VS). Using the FTS with a multipass cell, we measure high precision broadband absorption spectra of CH4at 3.3 μm and NO at 5.25 μm, the latter for the first time with comb spectroscopy, and we detect atmospheric species (CH4, CO, CO2, and H2O) in air in the signal and idler ranges. Multiline fitting yields minimum detectable concentrations of 10-20  ppb Hz-1/2for CH4, NO, and CO. For the first time in the mid-infrared, we perform CF-VS using an enhancement cavity, a grating, and a single detector, and we measure the absorption spectrum of CH4and H2O in ambient air at ∼3.3  μm, reaching a 40 ppb concentration detection limit for CH4in 2 ms.
authors.forename: Amir
authors.initials: A
authors.lastname: Khodabakhsh
authors.forename: Venkata
authors.initials: V
authors.lastname: Ramaiah-Badarla
authors.forename: Lucile
authors.initials: L
authors.lastname: Rutkowski
authors.forename: Alexandra C
authors.initials: AC
authors.lastname: Johansson
authors.forename: Kevin F
authors.initials: KF
authors.lastname: Lee
authors.forename: Jie
authors.initials: J
authors.lastname: Jiang
authors.forename: Christian
authors.initials: C
authors.lastname: Mohr
authors.forename: Martin E
authors.initials: ME
authors.lastname: Fermann
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Foltynowicz