Mid-infrared continuous-filtering Vernier spectroscopy using a doubly resonant optical parametric oscillator

Abstract

We present a continuous-filtering Vernier spectrometer operating in the 3.15-3.4 µm range, based on a femtosecond doubly resonant optical parametric oscillator, a cavity with a finesse of 340, a grating mounted on a galvo scanner and two photodiodes. The spectrometer allows acquisition of one spectrum spanning 250 nm of bandwidth in 25 ms with 8 GHz resolution, sufficient for resolving molecular lines at atmospheric pressure. An active lock ensures good frequency and intensity stability of the consecutive spectra and enables continuous signal acquisition and efficient averaging. The relative frequency scale is calibrated using a Fabry-Perot etalon or, alternatively, the galvo scanner position signal. We measure spectra of pure CH 4 as well as dry and laboratory air and extract CH 4 and H 2 O concentrations by multiline fitting of model spectra. The figure of merit of the spectrometer is 1.7×10 −9 cm −1 Hz −1/2 per spectral element and the minimum detectable concentration of CH 4 is 360 ppt Hz -1/2 , averaging down to 90 ppt after 16 s.

Time-resolved continuous-filtering Vernier spectroscopy of H2O and OH radical in a flame

“…The frequency axis of the spectrum is calibrated using either the position information of the grating or spectral fringes introduced by a known etalon element. The acquisition time of a single spectrum is usually of the order of few tens of ms [29][30][31][32], limited by the scanning speed of the grating and/or the ring-down time of the cavity, as the scan needs to be adiabatic to avoid distortion in cavity mode profiles [29].…”

Laser spectroscopy for breath analysis: towards clinical implementation

“…Different broadband spectroscopic methods such as Virtually Imaged Phase Array (VIPA) spectroscopy [84], Vernier spectroscopy [85], and dual-comb spectroscopy [86,87] are also utilized in the MIR range yielding faster measurement times and/or higher detection sensitivity paving the way towards achieving the specifications needed for biomedical applications. In addition, the recent dual-comb spectroscopic results using a DFG [88] or an OPO [89] based on an Orientation Patterned Gallium Phosphide (OPGaP) crystal-a newly developed nonlinear material-extend the available detection wavelength range to 12 µm.…”

Optical Frequency Comb Faraday Rotation Spectroscopy

“…Further improvements in sensitivity can be obtained by improving the extinction ratio of the polarizers or increasing the interaction length through multiple passes [29] or by cavity enhancement [30,31]. While in this first demonstration we used an FTS to acquire broadband OFC-FRS spectra, the technique is compatible with other detection schemes of comb spectroscopy, for example with continuous Vernier filtering [32,33], which should allow faster acquisition and thus faster modulation of the magnetic field.…”