Probing methane in air with a midinfrared frequency comb source

Abstract

We employed a midinfrared frequency comb source for methane detection in ambient air. The transmitted spectra over a bandwidth of about 500 nm were recorded with an optical spectrum analyzer under various experimental conditions of different path lengths. The normalized absorption spectra were compared and fitted with simulations, yielding quantitative values of concentrations of methane and water vapor in the ambient air. The 3σ detection limit was ∼6.6×10 cm in ambient air for a broad spectral range, achieved with a path length of ∼590 m. This approach provides a broad spectral range, a large dynamic range, high sensitivity, and accurate calibration. The performed analysis of the residuals shows that an excellent agreement between the measured and calculated spectral profiles was obtained.

Long-wave infrared generation from femtosecond and picosecond optical parametric oscillators based on orientation-patterned gallium phosphide

“…Mid-infrared (mid-IR) absorption spectroscopy benefits from spatial coherence as it allows long path lengths to be investigated [1], and allows tight focusing for microspectroscopy [2]. Quantum cascade lasers (QCLs), while a commercially available and mature laser technology, are generally narrow linewidth offering limited tuning, though external cavity QCLs (EC-QCLs) have been demonstrated with considerable, rapid tuning [3,4], and there are also commercially available (EC-QCLs) containing several QCL chips, with wide tuning across the mid-IR (for example [5]).…”

Quantitative modeling of complex molecular response in coherent cavity-enhanced dual-comb spectroscopy

“…Optical frequency combs (OFCs) [1][2][3][4] enable increasingly precise applications of atomic and molecular spectroscopy [5], including primary thermometry [6,7], optical radiocarbon dating [8], sub-Doppler and Doppler-free spectroscopy [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], ultrafast and multidimensional spectroscopy [27][28][29][30], survey spectroscopy of molecular ions and cold molecules [31][32][33], and time-resolved spectroscopy for fundamental chemical kinetics [34][35][36][37]. Applied spectroscopies [38] also make novel use of optical frequency combs for actively monitoring greenhouse gas fluxes [39][40][41], methane for open-path detection [42] and unambiguous source attribution [43] and reactive atmospheric species [44], elucidating the chemical composition of combustion and open flames…”