Communication: Simplified two-beam rotational CARS signal generation demonstrated in 1D

Bohlin, Alexis; Patterson, Brian D.; Kliewer, Christopher J.

doi:10.1063/1.4793556

Cited by 90 publications

(37 citation statements)

References 22 publications

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“…The technique is particularly well-renowned for high-precision thermometry, robust applicability in luminous sooting flames, and good performance in large-scale technical combustion systems where many other laser diagnostics struggle [2][3][4][5][6][7]. CARS instruments for combustion have most often been based on Nd:YAG and dye laser setups that provide nanosecond-duration laser pulses, but there has been a recent surge in research [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] investigating the utility of femtosecond laser sources for potentially dramatic leaps forward in combustion diagnostics. Commercial femtosecond amplifiers offer kHz-scale repetition rates, allowing researchers to dramatically exceed the $10 Hz barrier posed by high-energy nanosecond laser systems, and approach the energy containing scales of some turbulent flames [23,26].…”

Section: Introductionmentioning

confidence: 99%

Hybrid fs/ps rotational CARS temperature and oxygen measurements in the product gases of canonical flat flames

Kearney

2015

Combustion and Flame

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a b s t r a c tA hybrid fs/ps pure-rotational coherent anti-Stokes Raman scattering (CARS) scheme is systematically evaluated over a wide range of flame conditions in the product gases of two canonical flat-flame burners. Near-transform-limited, broadband femtosecond pump and Stokes pulses impulsively prepare a rotational Raman coherence, which is later probed using a high-energy, frequency-narrow picosecond beam generated by the second-harmonic bandwidth compression scheme that has recently been demonstrated for rotational CARS generation in H 2 /air flat flames. The measured spectra are free of collision effects and nonresonant background and can be obtained on a single-shot basis at 1 kHz. The technique is evaluated for temperature/oxygen measurements in near-adiabatic H 2 /air flames stabilized on the Hencken burner for equivalence ratios of u = 0.20-1.20. Thermometry is demonstrated in hydrocarbon/air products for u = 0.75-3.14 in premixed C 2 H 4 /air flat flames on the McKenna burner. Reliable spectral fitting is demonstrated for both shot-averaged and single-laser-shot data using a simple phenomenological model. Measurement accuracy is benchmarked by comparison to adiabatic-equilibrium calculations for the H 2 /air flames, and by comparison with nanosecond CARS measurements for the C 2 H 4 /air flames. Quantitative accuracy comparable to nanosecond rotational CARS measurements is observed, while the observed precision in both the temperature and oxygen data is extraordinarily high, exceeding nanosecond CARS, and on par with the best published thermometric precision by femtosecond vibrational CARS in flames, and rotational femtosecond CARS at low temperature. Threshold levels of signal-to-noise ratio to achieve 1-2% precision in temperature and O 2 /N 2 ratio are identified. The results show that pure-rotational fs/ps CARS is a robust and quantitative tool when applied across a wide range of flame conditions spanning lean H 2 /air combustion to fuel-rich sooting hydrocarbon flames.

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Section: Introductionmentioning

confidence: 99%

Hybrid fs/ps rotational CARS temperature and oxygen measurements in the product gases of canonical flat flames

Kearney

2015

Combustion and Flame

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“…4 The spectral resolution of hybrid fs/ps CARS signal, furthermore, allows single-shot thermometry and multispecies measurements in reacting flows at repetition rates in the kHz range, 5,11,12,28 and several hybrid fs/ps CARS schemes have been used to probe gas-phase vibrational 5,6 and a) Author to whom correspondence should be addressed. Electronic mail: hans.stauffer@gmail.com rotational [7][8][9][10][11][12][29][30][31] CARS spectra. In addition to the multiplex nature of this newer probe technique, hybrid fs/ps CARS also provides the additional feature that Raman-active rotational/vibrational frequencies can be directly recovered; 1 they do not need to be deduced from time-dependent coherent oscillations observed in the spectrally dispersed CARS signal beam, as is the case in fs tr-CARS.…”

Section: Introductionmentioning

confidence: 99%

Time- and frequency-dependent model of time-resolved coherent anti-Stokes Raman scattering (CARS) with a picosecond-duration probe pulse

Stauffer¹,

Miller²,

Slipchenko³

et al. 2014

The Journal of Chemical Physics

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The hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) technique presents a promising alternative to either fs time-resolved or ps frequency-resolved CARS in both gas-phase thermometry and condensed-phase excited-state dynamics applications. A theoretical description of timedependent CARS is used to examine this recently developed probe technique, and quantitative comparisons of the full time-frequency evolution show excellent accuracy in predicting the experimental vibrational CARS spectra obtained for two model systems. The interrelated timeand frequency-domain spectral signatures of gas-phase species produced by hybrid fs/ps CARS are explored with a focus on gas-phase N2 vibrational CARS, which is commonly used as a thermometric diagnostic of combusting flows. In particular, we discuss the merits of the simple top-hat spectral filter typically used to generate the ps-duration hybrid fs/ps CARS probe pulse, including strong discrimination against non-resonant background that often contaminates CARS signal. It is further demonstrated, via comparison with vibrational CARS results on a time-evolving solvated organic chromophore, that this top-hat probe-pulse configuration can provide improved spectral resolution, although the degree of improvement depends on the dephasing timescales of the observed molecular modes and the duration and timing of the narrowband final pulse. Additionally, we discuss the virtues of a frequencydomain Lorentzian probe-pulse lineshape and its potential for improving the hybrid fs/ps CARS technique as a diagnostic in high-pressure gas-phase thermometry applications. The hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) technique presents a promising alternative to either fs time-resolved or ps frequency-resolved CARS in both gas-phase thermometry and condensed-phase excited-state dynamics applications. A theoretical description of time-dependent CARS is used to examine this recently developed probe technique, and quantitative comparisons of the full time-frequency evolution show excellent accuracy in predicting the experimental vibrational CARS spectra obtained for two model systems. The interrelated timeand frequency-domain spectral signatures of gas-phase species produced by hybrid fs/ps CARS are explored with a focus on gas-phase N 2 vibrational CARS, which is commonly used as a thermometric diagnostic of combusting flows. In particular, we discuss the merits of the simple top-hat spectral filter typically used to generate the ps-duration hybrid fs/ps CARS probe pulse, including strong discrimination against non-resonant background that often contaminates CARS signal. It is further demonstrated, via comparison with vibrational CARS results on a time-evolving solvated organic chromophore, that this top-hat probe-pulse configuration can provide improved spectral resolution, although the degree of improvement depends on the dephasing timescales of the observed molecular modes and the duration and timing of the narrowba...

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“…Recent years have seen steps towards direct one-dimensional (1D) and 2D CARS measurements in reacting flows. Bohlin and Kliewer [153][154][155][156] are pioneering these developments, and applications to practical combustion systems are becoming feasible. For example, the use of 1D-CARS to investigate the behavior of a jet flame impinging on a solid wall was demonstrated.…”

Section: Coherent Anti-stokes Raman Scatteringmentioning

confidence: 99%

Advanced Laser-Based Techniques for Gas-Phase Diagnostics in Combustion and Aerospace Engineering

Ehn

Zhu

et al. 2017

Appl Spectrosc

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Gaining information of species, temperature, and velocity distributions in turbulent combustion and high-speed reactive flows is challenging, particularly for conducting measurements without influencing the experimental object itself. The use of optical and spectroscopic techniques, and in particular laser-based diagnostics, has shown outstanding abilities for performing non-intrusive in situ diagnostics. The development of instrumentation, such as robust lasers with high pulse energy, ultra-short pulse duration, and high repetition rate along with digitized cameras exhibiting high sensitivity, large dynamic range, and frame rates on the order of MHz, has opened up for temporally and spatially resolved volumetric measurements of extreme dynamics and complexities. The aim of this article is to present selected important laser-based techniques for gas-phase diagnostics focusing on their applications in combustion and aerospace engineering. Applicable laser-based techniques for investigations of turbulent flows and combustion such as planar laser-induced fluorescence, Raman and Rayleigh scattering, coherent anti-Stokes Raman scattering, laser-induced grating scattering, particle image velocimetry, laser Doppler anemometry, and tomographic imaging are reviewed and described with some background physics. In addition, demands on instrumentation are further discussed to give insight in the possibilities that are offered by laser flow diagnostics.

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Communication: Simplified two-beam rotational CARS signal generation demonstrated in 1D

Cited by 90 publications

References 22 publications

Hybrid fs/ps rotational CARS temperature and oxygen measurements in the product gases of canonical flat flames

Hybrid fs/ps rotational CARS temperature and oxygen measurements in the product gases of canonical flat flames

Time- and frequency-dependent model of time-resolved coherent anti-Stokes Raman scattering (CARS) with a picosecond-duration probe pulse

Advanced Laser-Based Techniques for Gas-Phase Diagnostics in Combustion and Aerospace Engineering

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