Picosecond time-resolved pure-rotational coherent anti-Stokes Raman spectroscopy for N_2 thermometry

Seeger, Thomas; Kiefer, Johannes; Leipertz, Alfred; Patterson, Brian D.; Kliewer, Christopher J.; Settersten, Thomas B.

doi:10.1364/ol.34.003755

Cited by 63 publications

(57 citation statements)

References 13 publications

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“…Since the non-resonant contributions occur only when all laser beams are coincident they decay rapidly with increasing probe delay. The Raman coherence in contrast has a certain life-time and so the resonant signal may be generated after a suitable delay to suppress the non-resonant background [165][166][167]. In this case however the J-dependent collisional dephasing must be taken into account as it affects the temperature derived from time-delayed CARS spectra [168].…”

Section: Concentration Measurements and Thermometry Applicationsmentioning

confidence: 99%

Laser diagnostics and minor species detection in combustion using resonant four-wave mixing

Kiefer

Ewart

2011

Progress in Energy and Combustion Science

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Laser-based methods have transformed combustion diagnostics in the past few decades. The high intensity, coherence, high spectral resolution and frequency tunability available from laser radiation has provided powerful tools for studying microscopic processes and macroscopic phenomena in combustion by linear and nonlinear optical processes. This review focuses on nonlinear optical techniques based on resonant four-wave mixing for non-intrusive measurements of minor species in combustion. The importance of minor species such as reaction intermediates is outlined together with the challenges they present for detection and measurement in the hostile environments of flames, technical combustors, and engines. The limitations of conventional optical methods for such measurements are described and the particular advantages of coherent methods using nonlinear optical techniques are discussed.The basic physics underlying four-wave wave mixing processes and theoretical models for signal calculation are then presented together with a discussion of how combustion parameters may be derived from analysis of signals generated in various four-wave mixing processes. The most important four-wave mixing processes, in this context, are then reviewed:Degenerate Four-Wave Mixing (DFWM), Coherent Anti-Stokes Raman Scattering (CARS), Laser Induced Grating Spectroscopy (LIGS) and Polarization Spectroscopy (PS). In each case the fundamental physics is outlined to explain the particular properties and diagnostic advantages of each technique. The application of the methods mentioned to molecular physics studies of combustion species is then reviewed along with their application in measurement of concentration, temperature and other combustion parameters. Related nonlinear techniques and recent extensions to the ultra-fast regime are briefly reviewed. Finally practical considerations relevant to multi-dimensional and multi-species measurements, as well as applications in technical combustion systems are discussed.Keywords: nonlinear optical spectroscopy, four-wave mixing, combustion diagnostics, minor species detection, laser-induced gratings, polarization spectroscopy IntroductionEnergy from renewable sources such as solar and wind power is the goal of much current research and technological development. Combustion, however, is and is likely to remain for the foreseeable future, the most important energy source for heat, electrical power and especially for transportation. In technical combustion systems the chemical energy of fossil fuels such as coal, crude oil and natural gas is converted into heat through oxidation with oxygen from air. However, fossil fuel resources are limited and alternatives like biofuels [1] or novel technologies such as fuel cells [2] are not yet able to meet the demand. Consequently, for a sustainable use of fossil fuels it is desirable to further improve the efficiency, maintainability and reliability of existing combustion devices. Achieving such improvements depends upon an improved understanding of t...

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Section: Concentration Measurements and Thermometry Applicationsmentioning

confidence: 99%

Laser diagnostics and minor species detection in combustion using resonant four-wave mixing

Kiefer

Ewart

2011

Progress in Energy and Combustion Science

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131

112

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“…We demonstrate that the rate of rotational decoherence changes by more than an order of magnitude in this range of J values, and show that its dependence on J can be described by a simplified scaling law. 33.20.Sn, 33.20.Xx Rotational decoherence in dense gaseous media is an area of active research because of its importance in the fundamental understanding of the dissipative properties of gases, as well as in the practical aspects of thermochemistry and combustion research [1][2][3][4]. Laser control of molecular rotation has been successfully applied to numerous physical and chemical processes, in which long lived rotational coherence is essential (for a comprehensive review, see Ref.5).…”

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Effects of Ultrafast Molecular Rotation on Collisional Decoherence

et al. 2014

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Using an optical centrifuge to control molecular rotation in an extremely broad range of angular momenta, we study coherent rotational dynamics of nitrogen molecules in the presence of collisions. We cover the range of rotational quantum numbers between J = 8 and J = 66 at room temperature and study a cross-over between the adiabatic and non-adiabatic regimes of rotational relaxation, which cannot be easily accessed by thermal means. We demonstrate that the rate of rotational decoherence changes by more than an order of magnitude in this range of J values, and show that its dependence on J can be described by a simplified scaling law. 33.20.Sn, 33.20.Xx Rotational decoherence in dense gaseous media is an area of active research because of its importance in the fundamental understanding of the dissipative properties of gases, as well as in the practical aspects of thermochemistry and combustion research [1][2][3][4]. Laser control of molecular rotation has been successfully applied to numerous physical and chemical processes, in which long lived rotational coherence is essential (for a comprehensive review, see Ref.5).One of the most interesting aspects of the collisioninduced rotational decoherence is the question about its dependence on the speed of molecular rotation and temperature. From the very first experimental works on the topic [6,7], it was suggested that the rate of rotational relaxation should drop with increasing rotational quantum number J, i.e. that the faster molecular rotors are more robust with respect to collisions. This expectation stems from the intuitive "exponential-gap law" (EGL) according to which the decay rate decreases as exp[−∆E J /k B T ] with the increasing distance between the rotational levels ∆E J (here k B is the Boltzmann constant and T is the temperature of the gas). The refined version of EGL, known as the "energy corrected sudden" (ECS) approximation and introduced by DePristo et al. [8], is a popular model which successfully explained a large number of experimental observations [1,2,[9][10][11][12].The ECS theory describes the collisional decay rate in terms of an "adiabaticity parameter" a ≡ ω J τ c = ω J l c /v c , where ω J is the frequency of molecular rotation, τ c is the collision time, l c is a characteristic interaction length (usually determined empirically) and v c is the mean relative velocity between the collision partners. Since a = 2πτ c /T J (with T J being the rotation period), it may also be viewed as the angle, by which a molecule rotates during the collision process. When a π, the collision is sudden and the energy transfer does not depend on J. In the case of the finite duration of collisions, i.e. a π, the ECS model calls for scaling the decay rate with a J-and temperature-dependent correction factorwith '1/6' being specific to R −6 interaction potentials. In thermal ensembles, both the highest available ω J and the mean particle velocity v c scale equally with temperature. Hence, thermally accessible values of a do not increase with increasing T a...

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“…Such a variation in temperature would normally be accompanied by a factor of several hundred reduction in signal intensity in rotational CARS measurements. 19 However, by taking advantage of the significantly larger coherence dephasing rates encountered in lower temperature gas zones as opposed to high temperature zones, 21,22 a probe delay of 350 ps brings the CARS signal levels from both hot zones and cold zones to within a factor of 20 of each other, well within the 16-bit dynamic range of a typical CCD.…”

Section: (Right)mentioning

confidence: 99%

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

Bohlin

Patterson²,

Kliewer³

2013

The Journal of Chemical Physics

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We explore a novel phase matching scheme for gas-phase rotational coherent anti-Stokes Raman spectroscopy (CARS). The scheme significantly simplifies the employment of the technique in general. Two laser beams, one broadband and one narrowband, are crossed at arbitrary angle and the generated rotational CARS signal, copropagating with the probe beam, is isolated using a polarization gating technique. The effect of phase-vector mismatch for various experimental implementations was measured experimentally and compared to calculations. The spatial resolution of the current technique is improved by more than an order of magnitude over standard gas-phase CARS experimental arrangements, providing an interaction length of less than 50 μm when desired. Both the pump and Stokes photons originate from the broadband pulse, and are therefore automatically overlapped temporally and spatially. Significantly improved signal levels are achieved because of both the ease of alignment and the higher pulse energy available to the pump and Stokes fields. We demonstrate the technique for single-laser-shot 1D rotational CARS signal generation over approximately a 1 cm field in a flame.

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Picosecond time-resolved pure-rotational coherent anti-Stokes Raman spectroscopy for N_2 thermometry

Cited by 63 publications

References 13 publications

Laser diagnostics and minor species detection in combustion using resonant four-wave mixing

Laser diagnostics and minor species detection in combustion using resonant four-wave mixing

Effects of Ultrafast Molecular Rotation on Collisional Decoherence

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

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