Femtosecond CARS on H2

Lang, Tobias; Kompa, K. L.; Motzkus, Marcus

doi:10.1016/s0009-2614(99)00787-3

Cited by 114 publications

(62 citation statements)

References 17 publications

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“…[5][6][7][8][9][10][11][12] This probe technique has been developed as a variant of fs time-resolved CARS (tr-CARS), [13][14][15][16][17][18][19][20][21][22][23][24][25] the history of which has been described thoroughly in recent reviews. 26,27 Hybrid fs/ps CARS utilizes the same four-wave-mixing excitation scheme as does fs tr-CARS; however, the use of a time-delayed, narrowband, ps-duration probe pulse-rather than a broadband, fs-duration probe pulse-allows direct frequency-domain detection of Raman-active molecular states.…”

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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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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“…Temporal and spectral resolution of CARS spectroscopy is typically limited by the duration of the excitation pulses and their frequency bandwidth, respectively. Broadband femtosecond pulses, though advantageous for time-resolved CARS spectroscopy [2,11], offer poor spectral resolution. The latter can be improved by means of the pulse shaping technique [12,13] which modifies the amplitudes and phases of the spectral constituents of the pulse [14] (Fig.…”

Section: Pacs Numbersmentioning

confidence: 99%

Noise autocorrelation spectroscopy with coherent Raman scattering

Konorov

Hepburn

et al. 2007

Nature Phys

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Ultrafast lasers have become one of the most powerful tools in coherent nonlinear optical spectroscopy. Short pulses enable direct observation of fast molecular dynamics [1,2], whereas broad spectral bandwidth offers ways of controlling nonlinear optical processes [3,4] by means of quantum interferences [5]. Special care is usually taken to preserve the coherence of laser pulses as it determines the accuracy of a spectroscopic measurement. Here we present a new approach to coherent Raman spectroscopy based on deliberately introduced noise, which increases the spectral resolution, robustness and efficiency. We probe laser induced molecular vibrations using a broadband laser pulse with intentionally randomized amplitude and phase. The vibrational resonances result in and are identified through the appearance of intensity correlations in the noisy spectrum of coherently scattered photons. Spectral resolution is neither limited by the pulse bandwidth, nor sensitive to the quality of the temporal and spectral profile of the pulses. This is particularly attractive for the applications in microscopy[6], biological imaging [7] and remote sensing [8], where dispersion and scattering properties of the medium often undermine the applicability of ultrafast lasers. The proposed method combines the efficiency and resolution of a coherent process with the robustness of incoherent light. As we demonstrate here, it can be implemented by simply destroying the coherence of a laser pulse, and without any elaborate temporal scanning or spectral shaping commonly required by the frequency-resolved spectroscopic methods with ultrashort pulses. PACS numbers:We apply our method to coherent anti-Stokes Raman scattering (CARS), which has become the method of choice in nonlinear optical spectroscopy and microscopy [6,9] after the advent of powerful ultrafast lasers. As a third-order nonlinear process, femtosecond CARS exhibits high efficiency at low average laser power. High sensitivity to molecular structure enables detection of small quantities of complex molecules[10] and non-invasive biological imaging [7]. In CARS, pump and Stokes photons of frequencies ω p and ω S , respectively, excite molecular vibrations at frequency Ω = ω p − ω S (Fig. 1a). A probe photon at ω 0 is scattered off the coherent vibrations generating the anti-Stokes signal at frequency ω = (ω 0 +Ω). Temporal and spectral resolution of CARS spectroscopy is typically limited by the duration of the excitation pulses and their frequency bandwidth, respectively. Broadband femtosecond pulses, though advantageous for time-resolved CARS spectroscopy[2, 11], offer poor spectral resolution. The latter can be improved by means of the pulse shaping technique [12,13] which modifies the amplitudes and phases of the spectral constituents of the pulse [14] (Fig. 1b(i)). It enables selective excitation [4,15] or selective probing [16,17] of separate vibrational modes on the frequency scale narrower than the overall pulse bandwidth. Selective excitation is based on the coherent control...

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“…Lang et al [18] used fs-CARS of the H 2 molecule for determining molecular parameters and gas-phase temperature from the time-resolved oscillatory pattern of the Raman coherence following pump-Stokes excitation. Those parameters were determined from the width and the relative heights of the recurrence peaks.…”

Section: Introductionmentioning

confidence: 99%

MARC Data Collection- A Flawed Process

Toney¹

2008

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The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information ABSTRACTTime-resolved femtosecond coherent anti-Stokes Raman scattering (fs-CARS) spectroscopy of the nitrogen molecule is used for the measurement of temperature in atmospheric-pressure, near-adiabatic, hydrogen-air diffusion flames. The initial frequency-spread dephasing rate of the Raman coherence induced by the ultrafast (85 fs) Stokes and pump beams are used as a measure of gas-phase temperature. This initial frequency-spread dephasing rate of the Raman coherence is completely independent of collisions and depends on1yon the frequency spread of the Raman transitions at different temperatures. A simple theoretical model based on the assumption of impulsive excitation of Raman coherence is used to extract temperatures from time-resolved fs-CARS experimental signals. The extracted temperatures from fs-CARS signals are in excellent agreement with the theoretical temperatures calculated from an adiabatic equilibrium calculation. The estimated absolute accuracy and the precision of the measurement technique are found to be ±40 K and ±50 K, respectively, over the temperature range 1500-2500 K. Abstract Time-resolved femtosecond coherent anti-Stokes Raman scattering (fs-CARS) spectroscopy of the nitrogen molecule is used for the measurement of temperature in atmospheric-pressure, near-adiabatic, hydrogen-air diffusion flames. The initial frequency-spread dephasing rate of the Raman coherence induced by the ultrafast ($85 fs) Stokes and pump beams is used as a measure of gas-phase temperature. This initial frequency-spread dephasing rate of the Raman coherence is completely independent of collisions and depends only on the frequency spread of the Raman transitions at different temperatures. A simple theoretical model based on the assumption of impulsive excitation of Raman coherence is used to extract temperatures from time-resolved fs-CARS experimental signals. The extracted temperatures from fs-CARS signals are in excellent agreement with the theoretical temperatures calculated from an adiabatic equilibrium calculation. The estimated absolute accuracy and the precision of the measurement technique are found to be ±40 K and ±50 K, respectively, over the temperature range 1500-2500 K. SUBJECT TERMS

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Femtosecond CARS on H2

Cited by 114 publications

References 17 publications

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

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

Noise autocorrelation spectroscopy with coherent Raman scattering

MARC Data Collection- A Flawed Process

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