Near infrared frequency comb vernier spectrometer for broadband trace gas detection

Compact mode-locked Er-doped fiber laser for broadband cavity-enhanced spectroscopy

“…This corresponds to noise equivalent absorption of 5.5 × 10 −8 cm −1 in 50 ms, calculated as σ/L eff , where L eff = FL/π is the effective path length in the cavity, equal to 200 m. The corresponding figure of merit is 7.4 × 10 −10 cm −1 Hz −1/2 , calculated as σT 1/2 /(L eff M 1/2 ), where T is the acquisition time equal to 50 ms, and M is the number of spectral elements, given by the ratio of the acquired spectral range (1.2 THz) and the resolution (4.4 GHz). The sensitivity is thus similar to that obtained in a previous implementations of Vernier spectroscopy based on commercial Er-doped fiber frequency combs [25,31], indicating the potential of our compact source for quantitative and sensitive measurements.…”

“…Cavity-enhanced Fourier transform spectroscopy, either using DCS [19] or mechanical spectrometers [20], requires tight comb-cavity locking [21] and, in the case of DCS, either complex stabilization schemes [22] or adaptive sampling [23]. An alternative cavity-enhanced comb based technique uses Vernier filtering of the comb by the cavity [24][25][26][27]. In particular, the so-called continuous-filtering Vernier spectroscopy (CF-VS) [27,28], allows recording cavity enhanced molecular spectra over the entire spectral bandwidth of the femtosecond laser in tens of ms.…”

Robust, Fast and Sensitive Near-Infrared Continuous- Filtering Vernier Spectrometer

“…We record spectra of CO 2 covering 1.7 THz of bandwidth at 1575 nm, and of CH 4 , covering 2.7 THz at 1650 nm. The noise equivalent absorption at 1575 nm is 5 × 10 −9 cm −1 Hz −1/2 , which is better than in previous demonstrations of the technique in the same spectral region, using a spectrometer with the galvo scanner and the same Er-doped fiber laser [31] or a commercial comb source [29], or using a Czerny-Turner spectrometer with scanned mirror and a CCD camera [36]. Moreover, the demonstrated absorption sensitivity is comparable to that of other robust cavity-enhanced techniques, e.g.…”

Continuous Vernier filtering of an optical frequency comb for broadband cavity-enhanced molecular spectroscopy

“…They are defined by the repetition rate of the femtosecond oscillator f rep and by a carrier-envelop offset frequency f ceo translating the whole comb of a constant value comprised between 0 and f rep , each comb mode frequency being indexed by an integer n and defined as ν las n = n.f rep + f ceo . Several approaches [1,2,3,4,5,6,9] have been designed to combine OFC's with the extended path lengths associated with high finesse cavities, to attain high sensitivity in molecular absorption spectra. Some resolve the comb mode structure (with 1 GHz mode locked laser) [1,2], some are fast (around or below the ms timescale of acquisition) [3,4], some particularly sensitive (baseline noise around 10 −4 ) [5], but none truly exploit the full bandwidth of OFC, restricting the accessible spectral range to roughly a few hundred of wavenumbers, around ten percent of the entire range of a typical Titanium:Sapphir (Ti:Sa) modelocked laser.…”