Broadband dual-frequency comb spectroscopy in a rapid compression machine

Abstract

We demonstrate fiber mode-locked dual frequency comb spectroscopy for broadband, high resolution measurements in a rapid compression machine (RCM). We apply an apodization technique to improve the short-term signal-to-noise-ratio (SNR), which enables broadband spectroscopy at combustionrelevant timescales. We measure the absorption on 24345 individual wavelength elements (comb teeth) between 5967 and 6133 cm -1 at 704-µs time resolution during a 12-ms compression of a CH4-N2 mixture. We discuss the effect of the apodization technique on the absorption spectra, and apply an identical effect to the spectral model during fitting to recover the mixture temperature. The fitted temperature is compared against an adiabatic model, and found to be in good agreement with expected trends. This work demonstrates the potential of DCS to be used as an in situ diagnostic tool for broadband, high resolution, measurements in engine-like environments.

Dual-comb spectroscopy for high-temperature reaction kinetics

“…However, many broadband measurement techniques, such as Fourier Transform Infrared spectrometers or rapid-tuning broad-scan external cavity quantum cascade lasers [1], are mechanically limited to low time-resolutions. Advanced broadband diagnostics being developed without such mechanical limitations involve super-continuum and frequency-comb absorption spectroscopy [2][3][4][5][6][7][8][9].…”

“…Two frequency combs can be combined to help interpret the signal of multiple wavelengths simultaneously, a technique called dual-comb spectroscopy (DCS). Notable studies involving DCS include: the first dual-comb field diagnostic monitoring greenhouse gases [2], dual-combs in a rapid compression machine [8], and DCS used to study protein dynamics [10].…”

“…These studies did not use DCS but used a single frequency comb and diffraction grating to interpret the signal. The use of two frequency combs, dual-comb spectroscopy, has been applied to high-temperature, nonreacting conditions in a rapid compression machine by Draper et al at 704 µs time-resolution and also by Schroeder et al in the exhaust of a gas turbine at high temperatures and 10-60 s time-resolution [4,8]. Draper Efforts to extend DCS into the 3-20 µm region have involved distributed feedback generation DFG [14], optical parametric oscillators (OPO) [15][16][17], and quantum-cascadelaser (QCL) approaches [6,7,[18][19][20].…”

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

“…However, the detection bandwidth of absorption techniques based on continuous wave lasers such as wavelength modulation spectroscopy (WMS) [11,12] and cavity ring-down spectroscopy [13][14][15][16] is usually limited to 1-2 cm −1 [17,18]. Much larger detection bandwidth is provided by techniques based on broadband sources such as optical frequency combs [19][20][21], supercontinuum sources [22,23] and Fourier-domain mode-locked lasers [24]. Spectrometers employing these sources have been used to determine water concentration and/or temperature in combustion environments with time resolution of the order of hundreds of microseconds or milliseconds [21,[23][24][25].…”

Ultrafast laser-absorption spectroscopy for single-shot, mid-infrared measurements of temperature, CO, and CH4 in flames

“…While highly useful, the narrowband nature of this approach can: 1) limit the dynamic range of such diagnostics (3), 2) complicate measurements of molecules with broad spectra (e.g., at high pressures), and 3) often prevents multispecies measurements using a single light source. To address these issues, numerous researchers have developed broadband LAS diagnostics, typically with 10s to 1000s of cm −1 of spectral bandwidth (4)(5)(6)(7)(8)(9)(10)(11).…”