Abstract

A robust approach for acquiring background-free, multitransition absorption spectra under single-laser-shot conditions is demonstrated using broadband, ultrashort laser pulses. This technique—referred to as time-resolved optically gated absorption (TOGA)—exploits the inherent differences in timescales between broadband, femtosecond-duration light sources and the longer-duration responses of narrowband atomic or molecular absorption features. An optical temporal gate, based on frequency mixing via sum-frequency generation or difference-frequency generation, is used to isolate these long-lived time-domain absorption features from the ultrashort component associated with the broadband absorption light source. A proof-of-principle demonstration of TOGA is provided using atomic Rb as an absorbing medium. Application of this technique toward single-laser-shot simultaneous detection of hydroxyl radical concentration and the corresponding local temperature is also demonstrated in a reacting flow. These results indicate that TOGA can provide spectrally resolved, broadband, background-free absorption measurements at laser-source repetition rates.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

1. INTRODUCTION

Ultrafast laser sources, and femtosecond (fs)-duration sources in particular, exhibit many qualities of interest to a wide range of applications [13]. Inherent within ultrafast laser pulses is a broad spectral bandwidth, concomitant with the time–energy uncertainty relationship arising from the Fourier transform relationship between these two physical quantities. This bandwidth is beneficial in applications that require impulsive excitation of a broad spectrum of molecular transitions [1]. Additionally, ultrashort-pulse laser sources afford operation at high repetition rates, ranging from 1–10 kHz for typical amplified systems to 80–100 MHz for oscillator systems. Thus, such systems are of great interest to those scientific communities that require measurements to be made at comparable high repetition rates, typically under single-laser-shot conditions.

On initial consideration, the broad spectral bandwidths associated with fs-duration pulses are often viewed as detrimental to traditional spectroscopic approaches, particularly when applied to species with relatively sharp spectral features, such those associated with rotational and vibrational transitions as well as, in gas-phase species, the rovibronic structure present within electronic transitions. When considered more deeply, however, such spectral limitations only exist if the time–frequency relationship is ignored; in well-composed ultrafast-laser experiments, the spectral information associated with the material response is simply distributed between these two Fourier-related domains. Time-resolved fs coherent anti-Stokes Raman scattering (fs-CARS), for example, has long been understood to exhibit the same spectral characteristics as are present in traditional frequency-domain CARS spectroscopies, albeit with these spectroscopic characteristics detected in the time-dependent signatures of the observed pump–probe-type signal [46].

Fourier transform absorption spectroscopies [713] that utilize fs-duration pulses as a broadband light source—including dual-frequency-comb absorption spectroscopy [9,12,13]—also exploits this time-dependent behavior, typically by interfering a replica fs-duration pulse with the forward-scattered time-dependent molecular response, usually referred to as an optical free-induction decay (FID) [12,14]. This FID is simply the interfering, coherent time-domain response associated with the discrete spectral components of the molecular absorption spectrum, weighted by their corresponding absorption cross sections, following impulsive excitation. Thus, in these spectroscopies, a subsequent Fourier transform produces an absorption spectrum in the frequency domain. However, such approaches inherently require multiple pulses to complete a full time series required for the Fourier transformation process, and the resultant frequency-domain signal still retains the background component of the laser source. Recently, a few approaches have been developed to remove this background component, either via data processing algorithms following data acquisition [15] or via interferometric experimental approaches that result in removal of the impulsive component from the measured dual-comb signal [16,17]. Still, each of these approaches requires multiple-pulse data-acquisition processes that step through the temporal profile of the molecular response, thereby limiting the rate of data acquisition and the temporal resolution of the absorption measurement.

 figure: Fig. 1.

Fig. 1. (a) Background and transmitted spectra for OH absorption near 286 nm in a 25.4 mm long stoichiometric ${{\rm{C}}_2}{{\rm{H}}_4}$–air laminar flame 5 mm above the burner surface; (b) intensity ratio spectrum indicating frequency-dependent transmitted intensity ($I$) relative to the input intensity, ${I_0}$. Significant signal averaging is required to counteract the shot-to-shot intensity fluctuations of the ultraviolet input laser source.

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Significant emphasis has, in recent years, been placed on the development of noninvasive optical techniques exploiting the broadband characteristics of fs-duration laser pulses for applications that require single-laser-shot measurements (e.g.,  thermometric and species-concentration measurements in turbulent combustion environments), particularly with nonlinear techniques that allow capture of these time-dependent spectroscopic features within the frequency domain [6,1822]. Such spectrally resolved approaches, then, allow single-shot measurement of local temperature—via the inherent temperature dependence of the spectroscopic features of the target species—and species concentration, including via the exploitation of electronic resonances to allow detection of transient molecular species present in low concentrations [23]. Direct absorption techniques [24] utilizing single-laser-shot approaches that exploit the broadband characteristics of ultrafast laser sources, have not, to date, been developed as widely as these nonlinear approaches, however. These approaches, exemplified in Fig. 1, are hindered predominantly by the presence of background from the laser source that a) limits the dynamic range of the experimental signal and b) can introduce, via intensity fluctuations, shot-to-shot instabilities upon subtraction. Such approaches, therefore, either require significantly longer path lengths or, in cases where the working path length is short, have typically been limited to species present in high concentrations [24]. Moreover, broadband, fs-duration absorption appears to be counterintuitive from the point of view of the atomic or molecular species of interest. In spite of interaction between a given molecule and the light pulse on the order of tens to hundreds of fs, the resultant absorption features exhibit narrow linewidths, consistent with long, picosecond (ps)-duration or longer timescales. This apparent discrepancy is resolved, however, if the interaction is considered as a linear system response (i.e., atomic or molecular FID) following interaction with the input electric field. This atomic or molecular response, propagating out of phase with the fs-duration input pulse, exhibits transition-dependent dephasing lifetimes concomitant with the collisionally broadened linewidths of the associated transitions, typically persisting for ps to nanoseconds (ns).

In this work, we exploit the inherent differences in temporal behavior associated with long-lived molecular responses of gas-phase species and the impulsive, fs-duration broadband pulse with an approach referred to as time-resolved optically gated absorption (TOGA). In the TOGA approach, a ps duration gating pulse is used directly to capture the time separated molecular response, freeing it from the background associated with the broadband, impulsive, fs-duration absorption light source. This TOGA approach allows, under single-laser-shot conditions, a complete measurement of the absorption features of the molecule of interest with sufficient spectral bandwidth and resolution to be used for thermometric measurements of minor combustion species in reacting-flow environments.

2. EXPERIMENTAL CONFIGURATION

The optical setup used in these experiments is depicted schematically in Fig. 2; in this figure, schematic pairs of Fourier-related frequency-domain [($E(\omega)]$ and time-domain [($E(t)]$ electric fields are shown, respectively, in upper and lower panels at several positions along the component beam paths. The setup incorporates an amplified Ti:sapphire fs-duration laser source (Coherent Astrella, 1 kHz repetition rate, wavelength ${\sim}{{800}}\;{\rm{nm}}$; duration ${\sim}{{60 - 100}}\;{\rm{fs}}$), the output of which is split into two portions. One portion is used to produce the broadband absorption beam, which passes through the experimental sample. Experimental samples explored in this work include gaseous rubidium (Rb) and the hydroxyl (OH) radical. The gas-phase Rb sample is produced by heating a 150 mm long quartz cell containing solid Rb to 115°C. For OH, near-adiabatic ethylene–air flames were prepared using a 25.4 mm square Hencken calibration burner [25,26], employing ethylene:air equivalence ratios $\phi$ ranging from ${\sim}{0.5}$ to ${\sim}{1.5}$. In the examples discussed below involving atomic Rb, this absorption source is simply the transmitted portion of the Ti:sapphire output, reduced via beamsplitters to pulse energies ranging from 0.5 to 2 µJ. In the examples involving OH detection in a reacting flow, the Ti:sapphire fundamental output is used to pump an optical parametric amplifier (OPA, Coherent TOPAS Prime) with subsequent frequency upconversion capabilities (Coherent NirUVis Frequency Converter) to produce broadband, fs-duration pulses at ${\sim}{{307}}\;{\rm{nm}}$ with bandwidth (${\sim}{{270}}\;{\rm{c}}{{\rm{m}}^{- 1}}$ FWHM) to support ${\sim}{{55}}\;{\rm{fs}}$ pulse duration. No additional steps were taken to compress the pulse duration of this OH excitation source to the time–frequency transform limit, however.

 figure: Fig. 2.

Fig. 2. Schematic optical configuration of TOGA setup, including pairs of simulated optical electric fields (upper panel of pair: frequency-domain depiction; lower panel: time-domain depiction). In this setup, only the absorption beam is required to pass through the sample of interest (here, either a Rb cell or a flame containing transient OH radical). Panels (a) and (b) depict the ultrashort-pulse, broadband absorption beam prior to sample interaction. Following sample absorption, (c) and (d) depict the absorption beam containing atomic/molecular absorption features in the frequency domain (as narrow peaks) and time domain (long-lived response), respectively. The gating beam, also with (e) broad spectral bandwidth and (f) ultrashort-pulse duration traverses a delay line for temporal control; frequency narrowing is achieved with (g) and (h) a Fabry–Pérot étalon. (i) Temporal overlap of the gating and absorption pulses in a sum-frequency or difference-frequency generation (SFG or DFG) medium is afforded by adjusting the delay line. (j) The resultant time-domain upconverted (or downconverted) signal is (k) detected following spectral dispersion.

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The absorption beam [depicted schematically as the broadband ${E_{{\rm{abs}}}}(\omega)$ in Fig. 2(a) and the corresponding impulsive ultrashort-duration ${E_{{\rm{abs}}}}(t)$ in Fig. 2(b)] passes through the sample of interest, emanating with diminished spectral intensity at the frequencies of the corresponding absorption features of the medium [Fig. 2c)]; the corresponding time-domain absorption pulse therefore contains long-lived components associated with the molecular FID [Fig. 2(d)] in addition to the initial impulsive pulse associated with the broadband component of the absorption beam. This absorption beam is directed into a nonlinear crystal for temporal interaction with the gating-beam pulse.

A gating pulse is simultaneously produced along the gating-beam line using the fundamental output of the Ti:sapphire amplifier [${E_{{\rm{gate}}}}(\omega)$ in Fig. 2(e) and ${E_{{\rm{gate}}}}(t)$ in Fig. 2(f)], which is, unless noted otherwise below, directed into a Fabry–Pérot étalon [TecOptics, free-spectral range $({\rm{FSR}}) = {{288}}\;{\rm{c}}{{\rm{m}}^{- 1}}$; finesse ${\sim}{{109}}$]. When placed in the path of a broadband, fs-duration pulse, this étalon has been shown previously [22] to produce a highly time-asymmetric pulse with a rapidly rising (${\sim}{{200}}\;{\rm{fs}}$) onset and exponential decay [Fig. 2(h)] consistent with the ${\sim}{2.6}\;{\rm{c}}{{\rm{m}}^{- 1}}$ Lorentzian bandwidth. This decay exhibits further oscillatory structure concomitant with the transmission of adjacent étalon orders, producing spectral sidebands present in the transmitted frequency-domain spectrum of the gating pulse that are shifted by the FSR relative to the central transmitted frequency [Fig. 2(g)]. The delay of the gating pulse relative to that of the absorption pulse can be adjusted using a translation stage placed along the gating-beam path. This gating pulse, therefore, can be delayed such that it arrives at a nonlinear crystal ($\alpha$-BBO, Type I, Newlight Photonics, ${{10}} \times {{10}} \times {0.25}\;{\rm{mm}}$) precisely delayed relative to the absorption pulse. This allows sum-frequency generation (SFG) or difference-frequency generation (DFG) of the long-lived molecular response while avoiding temporal overlap with the early, impulsive component of the absorption pulse [Fig. 2(i)], thereby rejecting upconversion/downconversion of the broadband background present in the absorption beam. The resultant TOGA time-domain electric field ${E_{{\rm{TOGA}}}}(t)$ [Fig. 2(j)] is then directed into a spectrometer (0.25 m for Rb gas examples; 1.25 m for OH examples) equipped with a CCD camera (Newton, Andor) to allow detection of the spectrally resolved TOGA signal intensity ${I_{{\rm{TOGA}}}}(\omega)$ [Fig. 2(k)].

3. RESULTS AND DISCUSSION

A. Rb Vapor

As an initial proof-of-principal setup, we have explored application of TOGA spectroscopy toward detection of atomic Rb, which exhibits resonant electronic transitions present at 794.760 nm and 780.027 nm, corresponding, respectively, to the ${{{5}}^2}{{\rm{P}}_{1/2}}\; \leftarrow \;{{{5}}^2}{{\rm{S}}_{1/2}}$ and ${{{5}}^2}{{\rm{P}}_{3/2}}\; \leftarrow \;{{{5}}^2}{{\rm{S}}_{1/2}}$ transitions. The broadband output of the amplified Ti:sapphire system has sufficient bandwidth to span this set of absorption transitions as depicted in Fig. 3.

 figure: Fig. 3.

Fig. 3. Absorption of broadband fs-duration pulse by Rb atom. Insets depict absorption features corresponding to Rb transitions near 780.0 nm and 794.8 nm.

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1. Ultrashort (fs-Duration) Gating Pulse

Prior to demonstrating the single-laser-shot detection approach as shown in Fig. 2, an initial exploration of the temporal response associated with this pair of optical transitions was completed. In that case, the Fabry–Pérot étalon was removed from the gating-pulse pathway, leaving a simple ${\sim}{{70}}\;{\rm{fs}}$ duration probe pulse for use in the external time-gating step. As such, the nearly impulsive probe gating pulse used in the upconversion step required a temporal scan to produce the time-domain signal associated with the atomic response present in the post-sample absorption-beam signal. As noted above, time gating was facilitated in the Rb case by SFG via mixing of the absorption pulse using a temporally scanned probe pulse with a spectral profile similar to the background spectrum shown in Fig. 3. The total integrated SFG signal was collected as a function of gating pulse delay, and the results of this temporal sweep are shown in Fig. 4. The observed signal exhibits an initial fs-duration burst associated with temporal overlap of the gating pulse with the impulsive, broadband background spectrum. Additional impulsive peaks are also observed at a handful of delays following this $t = {{0}}$ impulsive pulse; these peaks (at $t = {1.87}$, 3.20, 3.72 ps) result from weak secondary reflections from transmissive optics along the absorptive beam path, including the Rb cell windows. Persistent among these impulsive peaks, however, is the clear sinusoidal structure associated with the resonant atomic-species absorptive response. More specifically, this oscillation is dominated by the coherent beat frequency (${237.2}\;{\rm{c}}{{\rm{m}}^{- 1}}$) between the two resonant electronic transitions as shown in the inset Fourier transform of this time-dependent signal. This time-dependent oscillatory signal emphasizes the long-lived coherent behavior of the material response, present following resonant absorption, that can be exploited with careful time-domain gating of this transmitted signal transform of this time-dependent signal. This time-dependent oscillatory signal emphasizes the long-lived coherent behavior of the material response, present following resonant absorption, that can be exploited with careful time-domain gating of this transmitted signal.

 figure: Fig. 4.

Fig. 4. Time-domain atomic response of Rb probed by fs-duration gating pulse. An oscillatory component resulting from the beat between the two accessed transitions is observed (left inset) with beat frequency of ${237.2}\;{\rm{c}}{{\rm{m}}^{- 1}}$ (right inset).

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2. ps-Duration Gating Pulse

Although this time-dependent signal demonstrates that a nearly impulsive probe pulse can be used to recover the time-dependent atomic/molecular response of the absorbing species, such measurements are not conducive to single-laser-shot conditions, since a temporal sweep of the gating pulse is required to recover these response characteristics. In order to recover signal with sufficient spectral resolution for frequency-domain separation of spectral features, the temporal gate must have longer durations, as dictated by the Fourier-transform-limited frequency–time relationship. This spectral resolution is attained using an asymmetric ps-duration gating pulse [Fig. 2(h)] to provide SFG for only a portion of the delayed atomic response. A resultant TOGA spectrum obtained at a gating-pulse delay of 9.5 ps is shown in Fig. 5. At this and longer delays, two dominant peaks are observed in this spectrum, centered at 394.9 nm and 398.7 nm; these correspond to the frequency-shifted Rb transitions depicted in Fig. 3, observed at the SFG wavelengths associated with upconversion from the narrowband gating pulse centered at 799.8 nm (${{12}}\;{{503}}\;{\rm{c}}{{\rm{m}}^{- 1}}$). As noted above, the bandwidth of the initial broadband pulse results in significant transmission of additional narrowband components through the étalon, shifted by the ${{288}}\;{\rm{c}}{{\rm{m}}^{- 1}}$ FSR of the étalon; thus, an additional pair of blue-shifted peaks are observed in the TOGA spectrum shown in Fig. 5. Although they are not shown here, TOGA spectra observed near ${t} = {{0}}$ exhibit strong contribution from the broadband background of the absorption pulse, manifested here as a broadband background spanning ${\sim}{{4}}\;{\rm{nm}}$ (FWHM) across the upconverted wavelength range. Weaker replicas of this broadband background are also observed at delays associated with the delayed replica impulsive peaks that were present in the purely time-domain TOGA signal shown in Fig. 4; thus, a longer gating-pulse delay of 9.5 ps was used to remove these broadband background components in Fig. 5. Beyond this delay, the only temporal dependence of the observed TOGA signal resulted from a relatively uniform decay of the resonant peaks present in Fig. 5.

 figure: Fig. 5.

Fig. 5. Single-laser-shot TOGA signal from Rb produced using a narrowband gating pulse shaped using an étalon with a ${{288}}\;{\rm{c}}{{\rm{m}}^{- 1}}$ FSR, delayed to ${\sim}{9.5}\;{\rm{ps}}$ following the impulsive, broadband component of the absorption pulse. The $x$ axis represents the measured transition frequency following subtraction of the peak frequency of the upconverting gating pulse from the measured TOGA frequency. Major peaks correspond to the Rb transitions at 794.8 nm and 780.0 nm. Two replica peaks are also observed, resulting from transitions upconverted by an adjacent étalon order, blue-shifted by the FSR.

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B. OH Radical in Flame

The primary motivation for the initial development of TOGA lies in the potential of this approach to allow single-laser-shot, background-free, multitransition detection. Thus, this approach was applied toward OH radical detection in combusting environments, using DFG within the gating medium. The absorption pulse was tuned to ${\sim}{{307}}\;{\rm{nm}}$ to access the (0,0) bandhead of the ${\rm{A}}\; \leftarrow \;{\rm{X}}$ electronic transition of OH [27,28]; use of the gating pulse centered at 800 nm produced TOGA signal near 500 nm that was spectrally dispersed for detection. Example single-laser-shot TOGA spectra of OH are shown in Fig. 6; in these spectra, the photon energy of the gating pulse has been added to shift the observed spectra to the corresponding transition frequencies. Also included in the figure [Fig. 6(a)] is a stick spectrum of the absorption coefficients of the transition branches that contribute in this spectral regime. Note that these peaks have not been scaled by the temperature-dependent initial rotational ($N$-dependent) populations and are intended only to show the positions of expected transitions. The experimental spectra shown here correspond to ethylene:air equivalence ratios of $\phi=0.98$ [nearly stoichiometric; Fig. 6(b)] and $\phi=0.58$ [fuel lean; Fig. 6(c)], measured at a gating-pulse delay of 6.9 ps after the peak associated with the broadband absorption pulse.

 figure: Fig. 6.

Fig. 6. Example single-laser-shot TOGA spectra of OH in a reacting flow. (a) Absorption coefficients of relevant OH (0,0) transition branches in this region; (b) and (c) example TOGA spectra at fuel:air equivalence ratios ($\phi$) of 0.98 and 0.58, respectively. Corresponding simulated spectra are included, calculated at the denoted best-fit temperature for these selected spectra.

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The graphs in Fig. 6 also include the calculated TOGA spectra corresponding to the best-fit temperature for these single-shot spectra. These computational spectra have been calculated by a) simulating the frequency-domain broadband electric field associated with the experimental absorption-beam pulse; b) subtracting the temperature-dependent frequency-domain molecular response of OH [23,29]; and c) convolving this absorption spectrum—via a product following Fourier transform into the time domain—with a time-delayed simulation of the étalon-modified gating pulse. As such, these simulated spectra account for the spectral profiles (and corresponding time-domain behaviors) of both the broadband absorption pulse and the narrowband gating pulse that contains weak spectral sidebands produced by transmission of adjacent étalon orders. Least-squares fitting was used to determine best-fit temperatures for each measured TOGA spectrum; two best-fit examples are included in Fig. 6.

It is important to note that weak impulsive pulse replicas appearing at short delays, similar to those observed in the Rb cases above (Fig. 4), were also observed to be present in the absorption beam, producing some residual broadband background in the observed signal at gating-pulse delays earlier than the selected 6.9 ps delay. This effect reduces, to some extent, the potential signal levels observed for background-free detection of OH; still, the single-shot results measured over this range of flame conditions exhibited excellent signal-to-noise ratios and correspondingly good fits to allow determination of signal temperature and species concentration. This holds true even for the $\phi = {0.58}$ case, where the calculated OH adiabatic concentration is ${\sim}{{400}}\;{\rm{ppm}}$. The gating-pulse width (${\sim}{2.6}\;{\rm{c}}{{\rm{m}}^{- 1}}$), moreover, is sufficient to allow resolution of several of the major peaks within this spectral range; however, the transitions’ frequencies within the region near ${{32}},\!{{550}}\;{\rm{c}}{{\rm{m}}^{- 1}}$ become somewhat congested as compared to this gating pulse width. As a result, the spectral profile in that region is strongly delay dependent, changing notably with only 100 fs change in gating-pulse delay. Thus, in spite of frequency-domain spectral resolution that is limited by the gating-pulse linewidth, the contributions of all transitions within this spectral region contribute to the overall shape of the observed spectrum and the corresponding accuracy and precision of the measured temperature. It should be noted that the gating pulse used in these OH experiments was produced using a fundamental laser source with a narrower bandwidth (${\sim}{{16}}\;{\rm{nm}}$ near a central wavelength of 800 nm) than is depicted Fig. 3. As a result, the spectral sidebands—resulting from different étalon orders shifted by ${{288}}\;{\rm{c}}{{\rm{m}}^{- 1}}$ relative to peak transmission—of the étalon-narrowed gating pulse are significantly reduced; thus, the spectrally shifted replicas of the OH spectra were observed to be more than an order of magnitude weaker than the spectra shown here. Still, because the modeled simulation of the TOGA spectra incorporates the measured gating-pulse spectrum—including all transmitted peaks associated with the multiple étalon modes—any spectral interference associated with these shifted spectra are accounted for in the simulation.

Several single-shot data sets were obtained over a range of fuel:air equivalence ratios ($\phi$) to allow statistical determination of the accuracies and precisions of the measured temperature and relative species concentration using the TOGA approach. For each $\phi$, statistics of best-fit temperatures and concentrations were obtained for 1000 laser shots. The results of this analysis are shown in Fig. 7, depicting both the best-fit temperatures $T$ and signal scaling factors extracted from the fitting process. A direct comparison is also shown to the calculated temperatures and OH concentrations for adiabatic flames over this range of equivalence ratios [Fig. 7(a)]. Calculated temperatures across this range agree with the theoretical adiabatic temperatures to within 3.1%, with corresponding ${{1 }}\text{-}\sigma$ uncertainties of ${\lt}{3.0}\%$; these temperature accuracies and precisions are better in cases where stronger OH TOGA signal is observed, falling to 2.1% and ${\lt}{1.7}\%$, respectively, within the $\phi=0.65$$1.3$ range, where OH concentrations are stronger. These accuracies and precisions are comparable to those obtained using fully resonant electronically enhanced CARS (FREE-CARS) [23]. Similarly, the relative intensities of the OH signal scale well with the calculated adiabatic OH concentrations, although some discrepancies are present across this range. These adiabatic concentrations, however, have been shown previously [23,26] to deviate from measured OH concentrations; good agreement is observed [Fig. 7(b)] when these TOGA results are compared to corresponding relative OH concentrations measured using FREE-CARS [23]. Better characterization of the concentration dependence and sensitivity of the TOGA approach utilizing species where concentrations can be more readily controlled are currently being carried out.

 figure: Fig. 7.

Fig. 7. Best-fit $T$ and scaled OH number density TOGA results as a function of $\phi$, obtained 10 mm above Hencken burner surface. Symbols represent averages; error bars depict ${{1}}\sigma$ from 1000 best-fit single-shot spectra. (a) Best-fit ${T_{{\rm avg}}}$ (symbols) and calculated equilibrium $T$ (curve); (b) scaled OH number density from TOGA, OH number density determined from FREE-CARS measurements (dashed curve), and equilibrium OH number density (solid curve, right axis).

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4. CONCLUSIONS

In summary, we have demonstrated the use of a time-resolved optical gating approach—namely, frequency up/downconversion using a time-delayed ps-duration probe pulse—to isolate the atomic/molecular absorption features from the broadband background associated with the fs-duration impulsive pulse. This TOGA approach, therefore, allows sufficiently sensitive detection of minor species, such as OH in the presence of other major gas-phase combustion species, under single-laser-shot conditions. The broadband nature of this approach results in simultaneous detection of many transitions within the bandwidth of the fs-duration excitation pulse. The gating-pulse duration is sufficiently long to allow spectral separation of the contributing transitions, allowing, for example, accurate and precise determination of local temperature along the absorption beam line of sight; moreover, the duration and delay of the gating pulse can be limited to timescales that are short compared to collisional timescales, thereby minimizing the effects of molecular collisions on the observed peak intensities, analogous to hybrid fs/ps CARS experiments utilizing a similar asymmetric ps-duration pulse [30]. Although applied here using visible/ultraviolet absorption transitions in example atomic (Rb) and diatomic (OH) species, this TOGA approach is robust in that it is generally applicable to all absorption processes in which the transition linewidths are narrow as compared to the broadband fs-duration absorption light source, thereby resulting in a strong separation in the timescales between this impulsive excitation source and the long-duration system response. Moreover, the frequency shifting necessitated by the up/downconversion gating process should prove advantageous in many cases where spectrally resolved detection of the absorption spectrum is challenging, such as in the mid-infrared spectral regime.

Funding

Air Force Office of Scientific Research (LRIR: 18RQCOR097); Air Force Research Laboratory (FA8650-15-D-2518).

Acknowledgment

We thank Jake Schmidt and Jared Brutcher for assistance in acquiring data and Daniel Richardson and Sean Kearney for illuminating discussions associated with this work. This work has been cleared for public release by the Air Force Research Laboratory (88ABW-2020-1596).

Disclosures

HUS: Spectral Energies, LLC (E); PSH: Spectral Energies, LLC (E); SR: Spectral Energies, LLC (E).

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20. S. Roy, W. D. Kulatilaka, D. R. Richardson, R. P. Lucht, and J. R. Gord, “Gas-phase single-shot thermometry at 1 kHz using fs-CARS spectroscopy,” Opt. Lett. 34, 3857–3859 (2009). [CrossRef]  

21. S. Roy, N. Jiang, H. U. Stauffer, J. B. Schmidt, W. D. Kulatilaka, T. R. Meyer, C. E. Bunker, and J. R. Gord, “Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles,” J. Appl. Phys. 113, 184310 (2013). [CrossRef]  

22. D. R. Richardson, H. U. Stauffer, S. Roy, and J. R. Gord, “Comparison of chirped-probe-pulse and hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for combustion thermometry,” Appl. Opt. 56, E37–E49 (2017). [CrossRef]  

23. P. J. Wrzesinski, H. U. Stauffer, J. B. Schmidt, S. Roy, and J. R. Gord, “Single-shot thermometry and OH detection via femtosecond fully resonant electronically enhanced CARS (FREE-CARS),” Opt. Lett. 41, 2021–2024 (2016). [CrossRef]  

24. R. J. Tancin, Z. Chang, M. Gu, V. Radhakrishna, R. P. Lucht, and C. S. Goldenstein, “Ultrafast laser-absorption spectroscopy for single-shot, mid-infrared measurements of temperature, CO, and CH4 in flames,” Opt. Lett. 45, 583–586 (2020). [CrossRef]  

25. R. D. Hancock, K. E. Bertagnolli, and R. P. Lucht, “Nitrogen and hydrogen CARS temperature measurements in a hydrogen/air flame using a near-adiabatic flat-flame burner,” Combust. Flame 109, 323–331 (1997). [CrossRef]  

26. T. R. Meyer, S. Roy, T. N. Anderson, J. D. Miller, V. R. Katta, R. P. Lucht, and J. R. Gord, “Measurements of OH mole fraction and temperature up to 20 kHz by using a diode-laser-based UV absorption sensor,” Appl. Opt. 44, 6729–6740 (2005). [CrossRef]  

27. M. Tamura, P. A. Berg, J. E. Harrington, J. Luque, J. B. Jeffries, G. P. Smith, and D. R. Crosley, “Collisional quenching of CH(A), OH(A), and NO(A) in low pressure hydrocarbon flames,” Combust. Flame 114, 502–514 (1998). [CrossRef]  

28. J. Luque and D. R. Crosley, “LIFBASE: database and spectral simulation program (Version 1.5),” SRI International Report MP 99-009 (1999).

29. H. U. Stauffer, S. Roy, W. D. Kulatilaka, and J. R. Gord, “Detailed calculation of hydroxyl (OH) radical two-photon absorption via broadband ultrafast excitation,” J. Opt. Soc. Am. B 29, 40–52 (2012). [CrossRef]  

30. H. U. Stauffer, K. A. Rahman, M. N. Slipchenko, S. Roy, J. R. Gord, and T. R. Meyer, “Interference-free hybrid fs/ps vibrational CARS thermometry in high-pressure flames,” Opt. Lett. 43, 4911–4914 (2018). [CrossRef]  

References

  • View by:

  1. S. Roy, J. R. Gord, and A. K. Patnaik, “Recent advances in coherent anti-Stokes Raman scattering spectroscopy: Fundamental developments and applications in reacting flows,” Prog. Energy Combust. Sci. 36, 280–306 (2010).
    [Crossref]
  2. A. K. Patnaik, I. Adamovich, J. R. Gord, and S. Roy, “Recent advances in ultrafast-laser-based spectroscopy and imaging for reacting plasmas and flames,” Plasma Sources Sci. Technol. 26, 103001 (2017).
    [Crossref]
  3. N. Picqué and T. W. Hänsch, “Frequency comb spectroscopy,”Nat. Photonics 13, 146–157 (2019).
    [Crossref]
  4. T. Siebert, M. Schmitt, T. Michelis, A. Materny, and W. Kiefer, “CCD broadband detection technique for the spectral characterization of the inhomogeneous signal in femtosecond time-resolved four-wave mixing spectroscopy,” J. Raman Spectrosc. 30, 807–813 (1999).
    [Crossref]
  5. P. Beaud, H. M. Frey, T. Lang, and M. Motzkus, “Flame thermometry by femtosecond CARS,” Chem. Phys. Lett. 344, 407–412 (2001).
    [Crossref]
  6. T. Lang and M. Motzkus, “Single-shot femtosecond coherent anti-Stokes Raman-scattering thermometry,” J. Opt. Soc. Am. B 19, 340–344 (2002).
    [Crossref]
  7. J. Mandon, G. Guelachvili, N. Picqué, F. Druon, and P. Georges, “Femtosecond laser Fourier transform absorption spectroscopy,” Opt. Lett. 32, 1677–1679 (2007).
    [Crossref]
  8. E. Sorokin, I. T. Sorokina, J. Mandon, G. Guelachvili, and N. Picqué, “Sensitive multiplex spectroscopy in the molecular fingerprint 2.4 µm region with a Cr2+:ZnSE femtosecond laser,” Opt. Express 15, 16540–16545 (2007).
    [Crossref]
  9. I. Coddington, W. C. Swann, and N. R. Newbury, “Coherent multiheterodyne spectroscopy using stabilized optical frequency combs,”Phys. Rev. Lett. 100, 013902 (2008).
    [Crossref]
  10. J. Mandon, E. Sorokin, I. T. Sorokina, G. Guelachvili, and N. Picqué, “Supercontinua for high-resolution absorption multiplex infrared spectroscopy,” Opt. Lett. 33, 285–287 (2008).
    [Crossref]
  11. J. Mandon, G. Guelachvili, and N. Picqué, “Fourier transform spectroscopy with a laser frequency comb,” Nat. Photonics 3, 99–102 (2009).
    [Crossref]
  12. I. Coddington, W. C. Swann, and N. R. Newbury, “Time-domain spectroscopy of molecular free-induction decay in the infrared,” Opt. Lett. 35, 1395–1397 (2010).
    [Crossref]
  13. I. Coddington, W. C. Swann, and N. R. Newbury, “Coherent dual-comb spectroscopy at high signal-to-noise ratio,” Phys. Rev. A 82, 043817 (2010).
    [Crossref]
  14. T. J. Hammond, S. Monchoce, C. M. Zhang, G. G. Brown, P. B. Corkum, and D. M. Villeneuve, “Femtosecond time-domain observation of atmospheric absorption in the near-infrared spectrum,” Phys. Rev. A 94, 063410 (2016).
    [Crossref]
  15. R. K. Cole, A. S. Makowiecki, N. Hoghooghi, and G. B. Rieker, “Baseline-free quantitative absorption spectroscopy based on cepstral analysis,” Opt. Express 27, 37920–37939 (2019).
    [Crossref]
  16. T. Tomberg, A. Muraviev, Q. T. Ru, and K. L. Vodopyanov, “Background-free broadband absorption spectroscopy based on interferometric suppression with a sign-inverted waveform,” Optica 6, 147–151 (2019).
    [Crossref]
  17. T. Buberl, P. Sulzer, A. Leitenstorfer, F. Krausz, and I. Pupeza, “Broadband interferometric subtraction of optical fields,” Opt. Express 27, 2432–2443 (2019).
    [Crossref]
  18. B. D. Prince, A. Chakraborty, B. M. Prince, and H. U. Stauffer, “Development of simultaneous frequency- and time-resolved coherent anti-Stokes Raman scattering for ultrafast detection of molecular Raman spectra,” J. Chem. Phys. 125, 044502 (2006).
    [Crossref]
  19. M. N. Slipchenko, B. D. Prince, S. C. Ducatman, and H. U. Stauffer, “Development of a simultaneously frequency- and time-resolved Raman-induced Kerr effect probe,” J. Phys. Chem. A 113, 135–140 (2009).
    [Crossref]
  20. S. Roy, W. D. Kulatilaka, D. R. Richardson, R. P. Lucht, and J. R. Gord, “Gas-phase single-shot thermometry at 1 kHz using fs-CARS spectroscopy,” Opt. Lett. 34, 3857–3859 (2009).
    [Crossref]
  21. S. Roy, N. Jiang, H. U. Stauffer, J. B. Schmidt, W. D. Kulatilaka, T. R. Meyer, C. E. Bunker, and J. R. Gord, “Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles,” J. Appl. Phys. 113, 184310 (2013).
    [Crossref]
  22. D. R. Richardson, H. U. Stauffer, S. Roy, and J. R. Gord, “Comparison of chirped-probe-pulse and hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for combustion thermometry,” Appl. Opt. 56, E37–E49 (2017).
    [Crossref]
  23. P. J. Wrzesinski, H. U. Stauffer, J. B. Schmidt, S. Roy, and J. R. Gord, “Single-shot thermometry and OH detection via femtosecond fully resonant electronically enhanced CARS (FREE-CARS),” Opt. Lett. 41, 2021–2024 (2016).
    [Crossref]
  24. R. J. Tancin, Z. Chang, M. Gu, V. Radhakrishna, R. P. Lucht, and C. S. Goldenstein, “Ultrafast laser-absorption spectroscopy for single-shot, mid-infrared measurements of temperature, CO, and CH4 in flames,” Opt. Lett. 45, 583–586 (2020).
    [Crossref]
  25. R. D. Hancock, K. E. Bertagnolli, and R. P. Lucht, “Nitrogen and hydrogen CARS temperature measurements in a hydrogen/air flame using a near-adiabatic flat-flame burner,” Combust. Flame 109, 323–331 (1997).
    [Crossref]
  26. T. R. Meyer, S. Roy, T. N. Anderson, J. D. Miller, V. R. Katta, R. P. Lucht, and J. R. Gord, “Measurements of OH mole fraction and temperature up to 20 kHz by using a diode-laser-based UV absorption sensor,” Appl. Opt. 44, 6729–6740 (2005).
    [Crossref]
  27. M. Tamura, P. A. Berg, J. E. Harrington, J. Luque, J. B. Jeffries, G. P. Smith, and D. R. Crosley, “Collisional quenching of CH(A), OH(A), and NO(A) in low pressure hydrocarbon flames,” Combust. Flame 114, 502–514 (1998).
    [Crossref]
  28. J. Luque and D. R. Crosley, “LIFBASE: database and spectral simulation program (Version 1.5),” SRI International Report MP 99-009 (1999).
  29. H. U. Stauffer, S. Roy, W. D. Kulatilaka, and J. R. Gord, “Detailed calculation of hydroxyl (OH) radical two-photon absorption via broadband ultrafast excitation,” J. Opt. Soc. Am. B 29, 40–52 (2012).
    [Crossref]
  30. H. U. Stauffer, K. A. Rahman, M. N. Slipchenko, S. Roy, J. R. Gord, and T. R. Meyer, “Interference-free hybrid fs/ps vibrational CARS thermometry in high-pressure flames,” Opt. Lett. 43, 4911–4914 (2018).
    [Crossref]

2020 (1)

2019 (4)

2018 (1)

2017 (2)

D. R. Richardson, H. U. Stauffer, S. Roy, and J. R. Gord, “Comparison of chirped-probe-pulse and hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for combustion thermometry,” Appl. Opt. 56, E37–E49 (2017).
[Crossref]

A. K. Patnaik, I. Adamovich, J. R. Gord, and S. Roy, “Recent advances in ultrafast-laser-based spectroscopy and imaging for reacting plasmas and flames,” Plasma Sources Sci. Technol. 26, 103001 (2017).
[Crossref]

2016 (2)

P. J. Wrzesinski, H. U. Stauffer, J. B. Schmidt, S. Roy, and J. R. Gord, “Single-shot thermometry and OH detection via femtosecond fully resonant electronically enhanced CARS (FREE-CARS),” Opt. Lett. 41, 2021–2024 (2016).
[Crossref]

T. J. Hammond, S. Monchoce, C. M. Zhang, G. G. Brown, P. B. Corkum, and D. M. Villeneuve, “Femtosecond time-domain observation of atmospheric absorption in the near-infrared spectrum,” Phys. Rev. A 94, 063410 (2016).
[Crossref]

2013 (1)

S. Roy, N. Jiang, H. U. Stauffer, J. B. Schmidt, W. D. Kulatilaka, T. R. Meyer, C. E. Bunker, and J. R. Gord, “Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles,” J. Appl. Phys. 113, 184310 (2013).
[Crossref]

2012 (1)

2010 (3)

S. Roy, J. R. Gord, and A. K. Patnaik, “Recent advances in coherent anti-Stokes Raman scattering spectroscopy: Fundamental developments and applications in reacting flows,” Prog. Energy Combust. Sci. 36, 280–306 (2010).
[Crossref]

I. Coddington, W. C. Swann, and N. R. Newbury, “Time-domain spectroscopy of molecular free-induction decay in the infrared,” Opt. Lett. 35, 1395–1397 (2010).
[Crossref]

I. Coddington, W. C. Swann, and N. R. Newbury, “Coherent dual-comb spectroscopy at high signal-to-noise ratio,” Phys. Rev. A 82, 043817 (2010).
[Crossref]

2009 (3)

J. Mandon, G. Guelachvili, and N. Picqué, “Fourier transform spectroscopy with a laser frequency comb,” Nat. Photonics 3, 99–102 (2009).
[Crossref]

M. N. Slipchenko, B. D. Prince, S. C. Ducatman, and H. U. Stauffer, “Development of a simultaneously frequency- and time-resolved Raman-induced Kerr effect probe,” J. Phys. Chem. A 113, 135–140 (2009).
[Crossref]

S. Roy, W. D. Kulatilaka, D. R. Richardson, R. P. Lucht, and J. R. Gord, “Gas-phase single-shot thermometry at 1 kHz using fs-CARS spectroscopy,” Opt. Lett. 34, 3857–3859 (2009).
[Crossref]

2008 (2)

I. Coddington, W. C. Swann, and N. R. Newbury, “Coherent multiheterodyne spectroscopy using stabilized optical frequency combs,”Phys. Rev. Lett. 100, 013902 (2008).
[Crossref]

J. Mandon, E. Sorokin, I. T. Sorokina, G. Guelachvili, and N. Picqué, “Supercontinua for high-resolution absorption multiplex infrared spectroscopy,” Opt. Lett. 33, 285–287 (2008).
[Crossref]

2007 (2)

2006 (1)

B. D. Prince, A. Chakraborty, B. M. Prince, and H. U. Stauffer, “Development of simultaneous frequency- and time-resolved coherent anti-Stokes Raman scattering for ultrafast detection of molecular Raman spectra,” J. Chem. Phys. 125, 044502 (2006).
[Crossref]

2005 (1)

2002 (1)

2001 (1)

P. Beaud, H. M. Frey, T. Lang, and M. Motzkus, “Flame thermometry by femtosecond CARS,” Chem. Phys. Lett. 344, 407–412 (2001).
[Crossref]

1999 (1)

T. Siebert, M. Schmitt, T. Michelis, A. Materny, and W. Kiefer, “CCD broadband detection technique for the spectral characterization of the inhomogeneous signal in femtosecond time-resolved four-wave mixing spectroscopy,” J. Raman Spectrosc. 30, 807–813 (1999).
[Crossref]

1998 (1)

M. Tamura, P. A. Berg, J. E. Harrington, J. Luque, J. B. Jeffries, G. P. Smith, and D. R. Crosley, “Collisional quenching of CH(A), OH(A), and NO(A) in low pressure hydrocarbon flames,” Combust. Flame 114, 502–514 (1998).
[Crossref]

1997 (1)

R. D. Hancock, K. E. Bertagnolli, and R. P. Lucht, “Nitrogen and hydrogen CARS temperature measurements in a hydrogen/air flame using a near-adiabatic flat-flame burner,” Combust. Flame 109, 323–331 (1997).
[Crossref]

Adamovich, I.

A. K. Patnaik, I. Adamovich, J. R. Gord, and S. Roy, “Recent advances in ultrafast-laser-based spectroscopy and imaging for reacting plasmas and flames,” Plasma Sources Sci. Technol. 26, 103001 (2017).
[Crossref]

Anderson, T. N.

Beaud, P.

P. Beaud, H. M. Frey, T. Lang, and M. Motzkus, “Flame thermometry by femtosecond CARS,” Chem. Phys. Lett. 344, 407–412 (2001).
[Crossref]

Berg, P. A.

M. Tamura, P. A. Berg, J. E. Harrington, J. Luque, J. B. Jeffries, G. P. Smith, and D. R. Crosley, “Collisional quenching of CH(A), OH(A), and NO(A) in low pressure hydrocarbon flames,” Combust. Flame 114, 502–514 (1998).
[Crossref]

Bertagnolli, K. E.

R. D. Hancock, K. E. Bertagnolli, and R. P. Lucht, “Nitrogen and hydrogen CARS temperature measurements in a hydrogen/air flame using a near-adiabatic flat-flame burner,” Combust. Flame 109, 323–331 (1997).
[Crossref]

Brown, G. G.

T. J. Hammond, S. Monchoce, C. M. Zhang, G. G. Brown, P. B. Corkum, and D. M. Villeneuve, “Femtosecond time-domain observation of atmospheric absorption in the near-infrared spectrum,” Phys. Rev. A 94, 063410 (2016).
[Crossref]

Buberl, T.

Bunker, C. E.

S. Roy, N. Jiang, H. U. Stauffer, J. B. Schmidt, W. D. Kulatilaka, T. R. Meyer, C. E. Bunker, and J. R. Gord, “Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles,” J. Appl. Phys. 113, 184310 (2013).
[Crossref]

Chakraborty, A.

B. D. Prince, A. Chakraborty, B. M. Prince, and H. U. Stauffer, “Development of simultaneous frequency- and time-resolved coherent anti-Stokes Raman scattering for ultrafast detection of molecular Raman spectra,” J. Chem. Phys. 125, 044502 (2006).
[Crossref]

Chang, Z.

Coddington, I.

I. Coddington, W. C. Swann, and N. R. Newbury, “Coherent dual-comb spectroscopy at high signal-to-noise ratio,” Phys. Rev. A 82, 043817 (2010).
[Crossref]

I. Coddington, W. C. Swann, and N. R. Newbury, “Time-domain spectroscopy of molecular free-induction decay in the infrared,” Opt. Lett. 35, 1395–1397 (2010).
[Crossref]

I. Coddington, W. C. Swann, and N. R. Newbury, “Coherent multiheterodyne spectroscopy using stabilized optical frequency combs,”Phys. Rev. Lett. 100, 013902 (2008).
[Crossref]

Cole, R. K.

Corkum, P. B.

T. J. Hammond, S. Monchoce, C. M. Zhang, G. G. Brown, P. B. Corkum, and D. M. Villeneuve, “Femtosecond time-domain observation of atmospheric absorption in the near-infrared spectrum,” Phys. Rev. A 94, 063410 (2016).
[Crossref]

Crosley, D. R.

M. Tamura, P. A. Berg, J. E. Harrington, J. Luque, J. B. Jeffries, G. P. Smith, and D. R. Crosley, “Collisional quenching of CH(A), OH(A), and NO(A) in low pressure hydrocarbon flames,” Combust. Flame 114, 502–514 (1998).
[Crossref]

J. Luque and D. R. Crosley, “LIFBASE: database and spectral simulation program (Version 1.5),” SRI International Report MP 99-009 (1999).

Druon, F.

Ducatman, S. C.

M. N. Slipchenko, B. D. Prince, S. C. Ducatman, and H. U. Stauffer, “Development of a simultaneously frequency- and time-resolved Raman-induced Kerr effect probe,” J. Phys. Chem. A 113, 135–140 (2009).
[Crossref]

Frey, H. M.

P. Beaud, H. M. Frey, T. Lang, and M. Motzkus, “Flame thermometry by femtosecond CARS,” Chem. Phys. Lett. 344, 407–412 (2001).
[Crossref]

Georges, P.

Goldenstein, C. S.

Gord, J. R.

H. U. Stauffer, K. A. Rahman, M. N. Slipchenko, S. Roy, J. R. Gord, and T. R. Meyer, “Interference-free hybrid fs/ps vibrational CARS thermometry in high-pressure flames,” Opt. Lett. 43, 4911–4914 (2018).
[Crossref]

D. R. Richardson, H. U. Stauffer, S. Roy, and J. R. Gord, “Comparison of chirped-probe-pulse and hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for combustion thermometry,” Appl. Opt. 56, E37–E49 (2017).
[Crossref]

A. K. Patnaik, I. Adamovich, J. R. Gord, and S. Roy, “Recent advances in ultrafast-laser-based spectroscopy and imaging for reacting plasmas and flames,” Plasma Sources Sci. Technol. 26, 103001 (2017).
[Crossref]

P. J. Wrzesinski, H. U. Stauffer, J. B. Schmidt, S. Roy, and J. R. Gord, “Single-shot thermometry and OH detection via femtosecond fully resonant electronically enhanced CARS (FREE-CARS),” Opt. Lett. 41, 2021–2024 (2016).
[Crossref]

S. Roy, N. Jiang, H. U. Stauffer, J. B. Schmidt, W. D. Kulatilaka, T. R. Meyer, C. E. Bunker, and J. R. Gord, “Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles,” J. Appl. Phys. 113, 184310 (2013).
[Crossref]

H. U. Stauffer, S. Roy, W. D. Kulatilaka, and J. R. Gord, “Detailed calculation of hydroxyl (OH) radical two-photon absorption via broadband ultrafast excitation,” J. Opt. Soc. Am. B 29, 40–52 (2012).
[Crossref]

S. Roy, J. R. Gord, and A. K. Patnaik, “Recent advances in coherent anti-Stokes Raman scattering spectroscopy: Fundamental developments and applications in reacting flows,” Prog. Energy Combust. Sci. 36, 280–306 (2010).
[Crossref]

S. Roy, W. D. Kulatilaka, D. R. Richardson, R. P. Lucht, and J. R. Gord, “Gas-phase single-shot thermometry at 1 kHz using fs-CARS spectroscopy,” Opt. Lett. 34, 3857–3859 (2009).
[Crossref]

T. R. Meyer, S. Roy, T. N. Anderson, J. D. Miller, V. R. Katta, R. P. Lucht, and J. R. Gord, “Measurements of OH mole fraction and temperature up to 20 kHz by using a diode-laser-based UV absorption sensor,” Appl. Opt. 44, 6729–6740 (2005).
[Crossref]

Gu, M.

Guelachvili, G.

Hammond, T. J.

T. J. Hammond, S. Monchoce, C. M. Zhang, G. G. Brown, P. B. Corkum, and D. M. Villeneuve, “Femtosecond time-domain observation of atmospheric absorption in the near-infrared spectrum,” Phys. Rev. A 94, 063410 (2016).
[Crossref]

Hancock, R. D.

R. D. Hancock, K. E. Bertagnolli, and R. P. Lucht, “Nitrogen and hydrogen CARS temperature measurements in a hydrogen/air flame using a near-adiabatic flat-flame burner,” Combust. Flame 109, 323–331 (1997).
[Crossref]

Hänsch, T. W.

N. Picqué and T. W. Hänsch, “Frequency comb spectroscopy,”Nat. Photonics 13, 146–157 (2019).
[Crossref]

Harrington, J. E.

M. Tamura, P. A. Berg, J. E. Harrington, J. Luque, J. B. Jeffries, G. P. Smith, and D. R. Crosley, “Collisional quenching of CH(A), OH(A), and NO(A) in low pressure hydrocarbon flames,” Combust. Flame 114, 502–514 (1998).
[Crossref]

Hoghooghi, N.

Jeffries, J. B.

M. Tamura, P. A. Berg, J. E. Harrington, J. Luque, J. B. Jeffries, G. P. Smith, and D. R. Crosley, “Collisional quenching of CH(A), OH(A), and NO(A) in low pressure hydrocarbon flames,” Combust. Flame 114, 502–514 (1998).
[Crossref]

Jiang, N.

S. Roy, N. Jiang, H. U. Stauffer, J. B. Schmidt, W. D. Kulatilaka, T. R. Meyer, C. E. Bunker, and J. R. Gord, “Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles,” J. Appl. Phys. 113, 184310 (2013).
[Crossref]

Katta, V. R.

Kiefer, W.

T. Siebert, M. Schmitt, T. Michelis, A. Materny, and W. Kiefer, “CCD broadband detection technique for the spectral characterization of the inhomogeneous signal in femtosecond time-resolved four-wave mixing spectroscopy,” J. Raman Spectrosc. 30, 807–813 (1999).
[Crossref]

Krausz, F.

Kulatilaka, W. D.

S. Roy, N. Jiang, H. U. Stauffer, J. B. Schmidt, W. D. Kulatilaka, T. R. Meyer, C. E. Bunker, and J. R. Gord, “Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles,” J. Appl. Phys. 113, 184310 (2013).
[Crossref]

H. U. Stauffer, S. Roy, W. D. Kulatilaka, and J. R. Gord, “Detailed calculation of hydroxyl (OH) radical two-photon absorption via broadband ultrafast excitation,” J. Opt. Soc. Am. B 29, 40–52 (2012).
[Crossref]

S. Roy, W. D. Kulatilaka, D. R. Richardson, R. P. Lucht, and J. R. Gord, “Gas-phase single-shot thermometry at 1 kHz using fs-CARS spectroscopy,” Opt. Lett. 34, 3857–3859 (2009).
[Crossref]

Lang, T.

T. Lang and M. Motzkus, “Single-shot femtosecond coherent anti-Stokes Raman-scattering thermometry,” J. Opt. Soc. Am. B 19, 340–344 (2002).
[Crossref]

P. Beaud, H. M. Frey, T. Lang, and M. Motzkus, “Flame thermometry by femtosecond CARS,” Chem. Phys. Lett. 344, 407–412 (2001).
[Crossref]

Leitenstorfer, A.

Lucht, R. P.

Luque, J.

M. Tamura, P. A. Berg, J. E. Harrington, J. Luque, J. B. Jeffries, G. P. Smith, and D. R. Crosley, “Collisional quenching of CH(A), OH(A), and NO(A) in low pressure hydrocarbon flames,” Combust. Flame 114, 502–514 (1998).
[Crossref]

J. Luque and D. R. Crosley, “LIFBASE: database and spectral simulation program (Version 1.5),” SRI International Report MP 99-009 (1999).

Makowiecki, A. S.

Mandon, J.

Materny, A.

T. Siebert, M. Schmitt, T. Michelis, A. Materny, and W. Kiefer, “CCD broadband detection technique for the spectral characterization of the inhomogeneous signal in femtosecond time-resolved four-wave mixing spectroscopy,” J. Raman Spectrosc. 30, 807–813 (1999).
[Crossref]

Meyer, T. R.

Michelis, T.

T. Siebert, M. Schmitt, T. Michelis, A. Materny, and W. Kiefer, “CCD broadband detection technique for the spectral characterization of the inhomogeneous signal in femtosecond time-resolved four-wave mixing spectroscopy,” J. Raman Spectrosc. 30, 807–813 (1999).
[Crossref]

Miller, J. D.

Monchoce, S.

T. J. Hammond, S. Monchoce, C. M. Zhang, G. G. Brown, P. B. Corkum, and D. M. Villeneuve, “Femtosecond time-domain observation of atmospheric absorption in the near-infrared spectrum,” Phys. Rev. A 94, 063410 (2016).
[Crossref]

Motzkus, M.

T. Lang and M. Motzkus, “Single-shot femtosecond coherent anti-Stokes Raman-scattering thermometry,” J. Opt. Soc. Am. B 19, 340–344 (2002).
[Crossref]

P. Beaud, H. M. Frey, T. Lang, and M. Motzkus, “Flame thermometry by femtosecond CARS,” Chem. Phys. Lett. 344, 407–412 (2001).
[Crossref]

Muraviev, A.

Newbury, N. R.

I. Coddington, W. C. Swann, and N. R. Newbury, “Coherent dual-comb spectroscopy at high signal-to-noise ratio,” Phys. Rev. A 82, 043817 (2010).
[Crossref]

I. Coddington, W. C. Swann, and N. R. Newbury, “Time-domain spectroscopy of molecular free-induction decay in the infrared,” Opt. Lett. 35, 1395–1397 (2010).
[Crossref]

I. Coddington, W. C. Swann, and N. R. Newbury, “Coherent multiheterodyne spectroscopy using stabilized optical frequency combs,”Phys. Rev. Lett. 100, 013902 (2008).
[Crossref]

Patnaik, A. K.

A. K. Patnaik, I. Adamovich, J. R. Gord, and S. Roy, “Recent advances in ultrafast-laser-based spectroscopy and imaging for reacting plasmas and flames,” Plasma Sources Sci. Technol. 26, 103001 (2017).
[Crossref]

S. Roy, J. R. Gord, and A. K. Patnaik, “Recent advances in coherent anti-Stokes Raman scattering spectroscopy: Fundamental developments and applications in reacting flows,” Prog. Energy Combust. Sci. 36, 280–306 (2010).
[Crossref]

Picqué, N.

Prince, B. D.

M. N. Slipchenko, B. D. Prince, S. C. Ducatman, and H. U. Stauffer, “Development of a simultaneously frequency- and time-resolved Raman-induced Kerr effect probe,” J. Phys. Chem. A 113, 135–140 (2009).
[Crossref]

B. D. Prince, A. Chakraborty, B. M. Prince, and H. U. Stauffer, “Development of simultaneous frequency- and time-resolved coherent anti-Stokes Raman scattering for ultrafast detection of molecular Raman spectra,” J. Chem. Phys. 125, 044502 (2006).
[Crossref]

Prince, B. M.

B. D. Prince, A. Chakraborty, B. M. Prince, and H. U. Stauffer, “Development of simultaneous frequency- and time-resolved coherent anti-Stokes Raman scattering for ultrafast detection of molecular Raman spectra,” J. Chem. Phys. 125, 044502 (2006).
[Crossref]

Pupeza, I.

Radhakrishna, V.

Rahman, K. A.

Richardson, D. R.

Rieker, G. B.

Roy, S.

H. U. Stauffer, K. A. Rahman, M. N. Slipchenko, S. Roy, J. R. Gord, and T. R. Meyer, “Interference-free hybrid fs/ps vibrational CARS thermometry in high-pressure flames,” Opt. Lett. 43, 4911–4914 (2018).
[Crossref]

D. R. Richardson, H. U. Stauffer, S. Roy, and J. R. Gord, “Comparison of chirped-probe-pulse and hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for combustion thermometry,” Appl. Opt. 56, E37–E49 (2017).
[Crossref]

A. K. Patnaik, I. Adamovich, J. R. Gord, and S. Roy, “Recent advances in ultrafast-laser-based spectroscopy and imaging for reacting plasmas and flames,” Plasma Sources Sci. Technol. 26, 103001 (2017).
[Crossref]

P. J. Wrzesinski, H. U. Stauffer, J. B. Schmidt, S. Roy, and J. R. Gord, “Single-shot thermometry and OH detection via femtosecond fully resonant electronically enhanced CARS (FREE-CARS),” Opt. Lett. 41, 2021–2024 (2016).
[Crossref]

S. Roy, N. Jiang, H. U. Stauffer, J. B. Schmidt, W. D. Kulatilaka, T. R. Meyer, C. E. Bunker, and J. R. Gord, “Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles,” J. Appl. Phys. 113, 184310 (2013).
[Crossref]

H. U. Stauffer, S. Roy, W. D. Kulatilaka, and J. R. Gord, “Detailed calculation of hydroxyl (OH) radical two-photon absorption via broadband ultrafast excitation,” J. Opt. Soc. Am. B 29, 40–52 (2012).
[Crossref]

S. Roy, J. R. Gord, and A. K. Patnaik, “Recent advances in coherent anti-Stokes Raman scattering spectroscopy: Fundamental developments and applications in reacting flows,” Prog. Energy Combust. Sci. 36, 280–306 (2010).
[Crossref]

S. Roy, W. D. Kulatilaka, D. R. Richardson, R. P. Lucht, and J. R. Gord, “Gas-phase single-shot thermometry at 1 kHz using fs-CARS spectroscopy,” Opt. Lett. 34, 3857–3859 (2009).
[Crossref]

T. R. Meyer, S. Roy, T. N. Anderson, J. D. Miller, V. R. Katta, R. P. Lucht, and J. R. Gord, “Measurements of OH mole fraction and temperature up to 20 kHz by using a diode-laser-based UV absorption sensor,” Appl. Opt. 44, 6729–6740 (2005).
[Crossref]

Ru, Q. T.

Schmidt, J. B.

P. J. Wrzesinski, H. U. Stauffer, J. B. Schmidt, S. Roy, and J. R. Gord, “Single-shot thermometry and OH detection via femtosecond fully resonant electronically enhanced CARS (FREE-CARS),” Opt. Lett. 41, 2021–2024 (2016).
[Crossref]

S. Roy, N. Jiang, H. U. Stauffer, J. B. Schmidt, W. D. Kulatilaka, T. R. Meyer, C. E. Bunker, and J. R. Gord, “Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles,” J. Appl. Phys. 113, 184310 (2013).
[Crossref]

Schmitt, M.

T. Siebert, M. Schmitt, T. Michelis, A. Materny, and W. Kiefer, “CCD broadband detection technique for the spectral characterization of the inhomogeneous signal in femtosecond time-resolved four-wave mixing spectroscopy,” J. Raman Spectrosc. 30, 807–813 (1999).
[Crossref]

Siebert, T.

T. Siebert, M. Schmitt, T. Michelis, A. Materny, and W. Kiefer, “CCD broadband detection technique for the spectral characterization of the inhomogeneous signal in femtosecond time-resolved four-wave mixing spectroscopy,” J. Raman Spectrosc. 30, 807–813 (1999).
[Crossref]

Slipchenko, M. N.

H. U. Stauffer, K. A. Rahman, M. N. Slipchenko, S. Roy, J. R. Gord, and T. R. Meyer, “Interference-free hybrid fs/ps vibrational CARS thermometry in high-pressure flames,” Opt. Lett. 43, 4911–4914 (2018).
[Crossref]

M. N. Slipchenko, B. D. Prince, S. C. Ducatman, and H. U. Stauffer, “Development of a simultaneously frequency- and time-resolved Raman-induced Kerr effect probe,” J. Phys. Chem. A 113, 135–140 (2009).
[Crossref]

Smith, G. P.

M. Tamura, P. A. Berg, J. E. Harrington, J. Luque, J. B. Jeffries, G. P. Smith, and D. R. Crosley, “Collisional quenching of CH(A), OH(A), and NO(A) in low pressure hydrocarbon flames,” Combust. Flame 114, 502–514 (1998).
[Crossref]

Sorokin, E.

Sorokina, I. T.

Stauffer, H. U.

H. U. Stauffer, K. A. Rahman, M. N. Slipchenko, S. Roy, J. R. Gord, and T. R. Meyer, “Interference-free hybrid fs/ps vibrational CARS thermometry in high-pressure flames,” Opt. Lett. 43, 4911–4914 (2018).
[Crossref]

D. R. Richardson, H. U. Stauffer, S. Roy, and J. R. Gord, “Comparison of chirped-probe-pulse and hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for combustion thermometry,” Appl. Opt. 56, E37–E49 (2017).
[Crossref]

P. J. Wrzesinski, H. U. Stauffer, J. B. Schmidt, S. Roy, and J. R. Gord, “Single-shot thermometry and OH detection via femtosecond fully resonant electronically enhanced CARS (FREE-CARS),” Opt. Lett. 41, 2021–2024 (2016).
[Crossref]

S. Roy, N. Jiang, H. U. Stauffer, J. B. Schmidt, W. D. Kulatilaka, T. R. Meyer, C. E. Bunker, and J. R. Gord, “Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles,” J. Appl. Phys. 113, 184310 (2013).
[Crossref]

H. U. Stauffer, S. Roy, W. D. Kulatilaka, and J. R. Gord, “Detailed calculation of hydroxyl (OH) radical two-photon absorption via broadband ultrafast excitation,” J. Opt. Soc. Am. B 29, 40–52 (2012).
[Crossref]

M. N. Slipchenko, B. D. Prince, S. C. Ducatman, and H. U. Stauffer, “Development of a simultaneously frequency- and time-resolved Raman-induced Kerr effect probe,” J. Phys. Chem. A 113, 135–140 (2009).
[Crossref]

B. D. Prince, A. Chakraborty, B. M. Prince, and H. U. Stauffer, “Development of simultaneous frequency- and time-resolved coherent anti-Stokes Raman scattering for ultrafast detection of molecular Raman spectra,” J. Chem. Phys. 125, 044502 (2006).
[Crossref]

Sulzer, P.

Swann, W. C.

I. Coddington, W. C. Swann, and N. R. Newbury, “Time-domain spectroscopy of molecular free-induction decay in the infrared,” Opt. Lett. 35, 1395–1397 (2010).
[Crossref]

I. Coddington, W. C. Swann, and N. R. Newbury, “Coherent dual-comb spectroscopy at high signal-to-noise ratio,” Phys. Rev. A 82, 043817 (2010).
[Crossref]

I. Coddington, W. C. Swann, and N. R. Newbury, “Coherent multiheterodyne spectroscopy using stabilized optical frequency combs,”Phys. Rev. Lett. 100, 013902 (2008).
[Crossref]

Tamura, M.

M. Tamura, P. A. Berg, J. E. Harrington, J. Luque, J. B. Jeffries, G. P. Smith, and D. R. Crosley, “Collisional quenching of CH(A), OH(A), and NO(A) in low pressure hydrocarbon flames,” Combust. Flame 114, 502–514 (1998).
[Crossref]

Tancin, R. J.

Tomberg, T.

Villeneuve, D. M.

T. J. Hammond, S. Monchoce, C. M. Zhang, G. G. Brown, P. B. Corkum, and D. M. Villeneuve, “Femtosecond time-domain observation of atmospheric absorption in the near-infrared spectrum,” Phys. Rev. A 94, 063410 (2016).
[Crossref]

Vodopyanov, K. L.

Wrzesinski, P. J.

Zhang, C. M.

T. J. Hammond, S. Monchoce, C. M. Zhang, G. G. Brown, P. B. Corkum, and D. M. Villeneuve, “Femtosecond time-domain observation of atmospheric absorption in the near-infrared spectrum,” Phys. Rev. A 94, 063410 (2016).
[Crossref]

Appl. Opt. (2)

Chem. Phys. Lett. (1)

P. Beaud, H. M. Frey, T. Lang, and M. Motzkus, “Flame thermometry by femtosecond CARS,” Chem. Phys. Lett. 344, 407–412 (2001).
[Crossref]

Combust. Flame (2)

M. Tamura, P. A. Berg, J. E. Harrington, J. Luque, J. B. Jeffries, G. P. Smith, and D. R. Crosley, “Collisional quenching of CH(A), OH(A), and NO(A) in low pressure hydrocarbon flames,” Combust. Flame 114, 502–514 (1998).
[Crossref]

R. D. Hancock, K. E. Bertagnolli, and R. P. Lucht, “Nitrogen and hydrogen CARS temperature measurements in a hydrogen/air flame using a near-adiabatic flat-flame burner,” Combust. Flame 109, 323–331 (1997).
[Crossref]

J. Appl. Phys. (1)

S. Roy, N. Jiang, H. U. Stauffer, J. B. Schmidt, W. D. Kulatilaka, T. R. Meyer, C. E. Bunker, and J. R. Gord, “Spatially and temporally resolved temperature and shock-speed measurements behind a laser-induced blast wave of energetic nanoparticles,” J. Appl. Phys. 113, 184310 (2013).
[Crossref]

J. Chem. Phys. (1)

B. D. Prince, A. Chakraborty, B. M. Prince, and H. U. Stauffer, “Development of simultaneous frequency- and time-resolved coherent anti-Stokes Raman scattering for ultrafast detection of molecular Raman spectra,” J. Chem. Phys. 125, 044502 (2006).
[Crossref]

J. Opt. Soc. Am. B (2)

J. Phys. Chem. A (1)

M. N. Slipchenko, B. D. Prince, S. C. Ducatman, and H. U. Stauffer, “Development of a simultaneously frequency- and time-resolved Raman-induced Kerr effect probe,” J. Phys. Chem. A 113, 135–140 (2009).
[Crossref]

J. Raman Spectrosc. (1)

T. Siebert, M. Schmitt, T. Michelis, A. Materny, and W. Kiefer, “CCD broadband detection technique for the spectral characterization of the inhomogeneous signal in femtosecond time-resolved four-wave mixing spectroscopy,” J. Raman Spectrosc. 30, 807–813 (1999).
[Crossref]

Nat. Photonics (2)

N. Picqué and T. W. Hänsch, “Frequency comb spectroscopy,”Nat. Photonics 13, 146–157 (2019).
[Crossref]

J. Mandon, G. Guelachvili, and N. Picqué, “Fourier transform spectroscopy with a laser frequency comb,” Nat. Photonics 3, 99–102 (2009).
[Crossref]

Opt. Express (3)

Opt. Lett. (7)

Optica (1)

Phys. Rev. A (2)

I. Coddington, W. C. Swann, and N. R. Newbury, “Coherent dual-comb spectroscopy at high signal-to-noise ratio,” Phys. Rev. A 82, 043817 (2010).
[Crossref]

T. J. Hammond, S. Monchoce, C. M. Zhang, G. G. Brown, P. B. Corkum, and D. M. Villeneuve, “Femtosecond time-domain observation of atmospheric absorption in the near-infrared spectrum,” Phys. Rev. A 94, 063410 (2016).
[Crossref]

Phys. Rev. Lett. (1)

I. Coddington, W. C. Swann, and N. R. Newbury, “Coherent multiheterodyne spectroscopy using stabilized optical frequency combs,”Phys. Rev. Lett. 100, 013902 (2008).
[Crossref]

Plasma Sources Sci. Technol. (1)

A. K. Patnaik, I. Adamovich, J. R. Gord, and S. Roy, “Recent advances in ultrafast-laser-based spectroscopy and imaging for reacting plasmas and flames,” Plasma Sources Sci. Technol. 26, 103001 (2017).
[Crossref]

Prog. Energy Combust. Sci. (1)

S. Roy, J. R. Gord, and A. K. Patnaik, “Recent advances in coherent anti-Stokes Raman scattering spectroscopy: Fundamental developments and applications in reacting flows,” Prog. Energy Combust. Sci. 36, 280–306 (2010).
[Crossref]

Other (1)

J. Luque and D. R. Crosley, “LIFBASE: database and spectral simulation program (Version 1.5),” SRI International Report MP 99-009 (1999).

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Figures (7)

Fig. 1.
Fig. 1. (a) Background and transmitted spectra for OH absorption near 286 nm in a 25.4 mm long stoichiometric ${{\rm{C}}_2}{{\rm{H}}_4}$–air laminar flame 5 mm above the burner surface; (b) intensity ratio spectrum indicating frequency-dependent transmitted intensity ($I$) relative to the input intensity, ${I_0}$. Significant signal averaging is required to counteract the shot-to-shot intensity fluctuations of the ultraviolet input laser source.
Fig. 2.
Fig. 2. Schematic optical configuration of TOGA setup, including pairs of simulated optical electric fields (upper panel of pair: frequency-domain depiction; lower panel: time-domain depiction). In this setup, only the absorption beam is required to pass through the sample of interest (here, either a Rb cell or a flame containing transient OH radical). Panels (a) and (b) depict the ultrashort-pulse, broadband absorption beam prior to sample interaction. Following sample absorption, (c) and (d) depict the absorption beam containing atomic/molecular absorption features in the frequency domain (as narrow peaks) and time domain (long-lived response), respectively. The gating beam, also with (e) broad spectral bandwidth and (f) ultrashort-pulse duration traverses a delay line for temporal control; frequency narrowing is achieved with (g) and (h) a Fabry–Pérot étalon. (i) Temporal overlap of the gating and absorption pulses in a sum-frequency or difference-frequency generation (SFG or DFG) medium is afforded by adjusting the delay line. (j) The resultant time-domain upconverted (or downconverted) signal is (k) detected following spectral dispersion.
Fig. 3.
Fig. 3. Absorption of broadband fs-duration pulse by Rb atom. Insets depict absorption features corresponding to Rb transitions near 780.0 nm and 794.8 nm.
Fig. 4.
Fig. 4. Time-domain atomic response of Rb probed by fs-duration gating pulse. An oscillatory component resulting from the beat between the two accessed transitions is observed (left inset) with beat frequency of ${237.2}\;{\rm{c}}{{\rm{m}}^{- 1}}$ (right inset).
Fig. 5.
Fig. 5. Single-laser-shot TOGA signal from Rb produced using a narrowband gating pulse shaped using an étalon with a ${{288}}\;{\rm{c}}{{\rm{m}}^{- 1}}$ FSR, delayed to ${\sim}{9.5}\;{\rm{ps}}$ following the impulsive, broadband component of the absorption pulse. The $x$ axis represents the measured transition frequency following subtraction of the peak frequency of the upconverting gating pulse from the measured TOGA frequency. Major peaks correspond to the Rb transitions at 794.8 nm and 780.0 nm. Two replica peaks are also observed, resulting from transitions upconverted by an adjacent étalon order, blue-shifted by the FSR.
Fig. 6.
Fig. 6. Example single-laser-shot TOGA spectra of OH in a reacting flow. (a) Absorption coefficients of relevant OH (0,0) transition branches in this region; (b) and (c) example TOGA spectra at fuel:air equivalence ratios ($\phi$) of 0.98 and 0.58, respectively. Corresponding simulated spectra are included, calculated at the denoted best-fit temperature for these selected spectra.
Fig. 7.
Fig. 7. Best-fit $T$ and scaled OH number density TOGA results as a function of $\phi$, obtained 10 mm above Hencken burner surface. Symbols represent averages; error bars depict ${{1}}\sigma$ from 1000 best-fit single-shot spectra. (a) Best-fit ${T_{{\rm avg}}}$ (symbols) and calculated equilibrium $T$ (curve); (b) scaled OH number density from TOGA, OH number density determined from FREE-CARS measurements (dashed curve), and equilibrium OH number density (solid curve, right axis).

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