Picosecond polarization-selective transient grating experiments in sodium-seeded flames

Fourkas, John T.; Brewer, Timothy R.; Kim, Hackjin; Fayer, M. D.

doi:10.1063/1.461599

Cited by 30 publications

(9 citation statements)

References 29 publications

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“…One important application of RFWM is the study of reacting gaseous media, including plasma 16 and combustion 17 environments. Measurements of molecular temperature, 18 -21 concentration, [22][23][24] and velocity distributions 25,26 have been demonstrated. In addition RFWM methods have been recently applied to double resonance spectroscopy of molecules 27 and to backgroundfree stimulated emission pumping spectroscopy of stable 28 and transient species.…”

Section: Introductionmentioning

confidence: 97%

Effects of different population, orientation, and alignment relaxation rates in resonant four-wave mixing

Williams

Rahn

Zare

1996

The Journal of Chemical Physics

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We present a combined theoretical and experimental study on the effects of different population, orientation, and alignment relaxation rates in resonant four-wave mixing ͑RFWM͒. Signal generation in RFWM can be viewed as the formation of and scattering from laser-induced population, orientation, and alignment gratings. We show that the relative contributions from the upper-state and lower-state population, orientation, and alignment gratings to the observed output signal can be changed by varying the polarizations of the three input fields. A theory is developed to account for these changes in collisional environments where the three multipole moments of the total angular momentum distribution, i.e., the population, the orientation, and the alignment, relax unequally. This theory is applied to the OH radical in an atmospheric-pressure H 2 /O 2 /He flame for which we have measured the line profiles using high-resolution degenerate and nearly degenerate four-wave mixing. We find that orientation and alignment gratings relax more rapidly than population gratings for low rotational levels of OH in the presence of He but at essentially the same rate for high rotational levels. A discussion is presented of the importance of this effect in the interpretation of RFWM experiments.

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Section: Introductionmentioning

confidence: 97%

Effects of different population, orientation, and alignment relaxation rates in resonant four-wave mixing

Williams

Rahn

Zare

1996

The Journal of Chemical Physics

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“…They used a dye laser at 308 nm to excited OH radicals and employed a pulsed probe laser (532 nm). Fourkas et al employed two picosecond lasers at 589.6 and 589.0 nm to resonantly pump and probe sodium atoms seeded into hydrogen and methane flames [12]. Hell et al [13] utilized the absorption band of water around 1 µm to obtain laser-induced thermal gratings in a H2/air flame using the fundamental output of a Nd:YAG laser.…”

Section: Introductionmentioning

confidence: 99%

“…For multi-parameter measurements, laser-induced thermal gratings seem to be more promising. In an optimal case, these thermal gratings are produced by excitation of species that naturally occur in a flame in order to avoid the need for seeding a tracer like acetone [23] or sodium [12]. Molecular tracers may be oxidized in the reaction zone and hence measurements are only possible in the unburnt gas region of a flame.…”

Section: Introductionmentioning

confidence: 99%

Mid-infrared laser-induced thermal grating spectroscopy in flames

Sahlberg

Hot

Kiefer

et al. 2017

Proceedings of the Combustion Institute

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For the first time, laser-induced thermal grating spectroscopy (LITGS) in the spectral range around 3 μm is demonstrated as a versatile diagnostic tool. This spectral region is of particular interest in combustion diagnostics as many relevant species such as hydrocarbons and water exhibit fundamental vibrational modes and hence can be probed with high sensitivity. Another benefit of the IR-LITGS is that it allows performing spectroscopy in the infrared combined with signal detection in the visible. Hence, the strong thermal radiation inherent in flames does not represent an interference. As the first step, we present the application of IR-LITGS to cold gas flows, where traces of ethylene and water vapor are detected. The time-resolved LITGS signals, which can be acquired in a single laser shot, are rich in information and allow deriving temperature and to some extend chemical composition. In the second step, the IR-LITGS technique is applied to ethylene/air flames stabilized on a flat flame burner. A proof-of-concept study is carried out, in which the temperature is determined in the burned region of flames with systematically varied equivalence ratio (0.72 < Φ < 2.57). Moreover, in a highly sooty flame, LITGS signals were recorded as a function of height above the burner and allowed the determination of the temperature profile. The proposed IR-LITGS method has the potential for enabling single-shot measurements of several parameters at a time. Its applicability to sooty flame environments opens up new opportunities to study the complex formation of carbonaceous particles in flames.

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“…Fourkas et al employed two picosecond lasers to resonantly pump and probe sodium atoms seeded into hydrogen and methane flames. 181 Hell et al 182 utilized the absorption band of water around 1 mm to obtain laserinduced thermal gratings in a H 2 /air flame. Methane/air flames were studied by Hart et al, 183 Hemmerling et al, 184 and Stampanoni-Panariello et al 185 All these works employed pump laser sources in the UV, visible, or near-infrared (NIR) spectral range.…”

Section: Laser-induced Grating Scattering (Ligs)mentioning

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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Picosecond polarization-selective transient grating experiments in sodium-seeded flames

Cited by 30 publications

References 29 publications

Effects of different population, orientation, and alignment relaxation rates in resonant four-wave mixing

Effects of different population, orientation, and alignment relaxation rates in resonant four-wave mixing

Mid-infrared laser-induced thermal grating spectroscopy in flames

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

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