Rotational CARS: a comparison of different techniques with emphasis on accuracy in temperature determination

Aldén, Marcus; Bengtsson, Per-Erik; Edner, Hans; Kröll, Stefan; Nilsson, David

doi:10.1364/ao.28.003206

Cited by 69 publications

(21 citation statements)

References 48 publications

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“…A more extensive investigation of the noise-and temperature-accuracy properties of rotational CARS, which may be compared with the present model, is in progress. 33 In practice, CC and RDBC may not give the same noise at all. The theoretical expressions in Eq.…”

Section: Discussionmentioning

confidence: 99%

Influence of laser-mode statistics on noise in nonlinear-optical processes—application to single-shot broadband coherent anti-Stokes Raman scattering thermometry

Kröll¹,

Sandell

1988

J. Opt. Soc. Am. B

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A quantitative approach for calculating the noise due to the stochastic nature of multimode laser radiation in nonlinear-optical processes is presented. The model is applicable when it is appropriate to describe the nonlinear interaction with a perturbation expansion in the incoming field, and it is derived under the assumption of independent individual laser-mode intensities and phases. It is possible to separate noise contributions from mode-amplitude and -phase fluctuations, respectively, and also to identify the noise contribution from each laser source. For coherent anti-Stokes Raman scattering (CARS) thermometry, the model shows that with a singlemode pump laser the stochastic phases in the dye laser do not generate noise in the conventional approach and that amplitude fluctuations in the dye laser(s) do not (significantly) generate noise in the dual-broadband approaches. Thus, in the dual-broadband approaches, the spectral noise in the Stokes beam is not a lower limit for the noise in the CARS beam. The model seems to overestimate the noise due to phase fluctuations and to underestimate the noise due to amplitude fluctuations.

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Section: Discussionmentioning

confidence: 99%

Influence of laser-mode statistics on noise in nonlinear-optical processes—application to single-shot broadband coherent anti-Stokes Raman scattering thermometry

Kröll¹,

Sandell

1988

J. Opt. Soc. Am. B

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“…With this technique, two broadband dye-laser beams combine into dual-broadband CARS to average many contributions to each rotational Raman resonance. Single-shot imprecision ranges from 4% to 5% at room temperature to 6% to 7% near 2000 K for measurements above a water-cooled porous-plug burner in the burnt gases of a premixed methane-air flame, 27 in hot air in a high-temperature oven, 24,28 -30 in convective heat transfer flows, 31 and at high pressures. 32,33 In an internal-combustion engine a 1% relative standard deviation was obtained, 34 but it is still not understood why these measurements ended up with lower relative standard deviations than detected in similar laboratory conditions.…”

Section: Introductionmentioning

confidence: 99%

“…9,10,12,24 It compares well with the best values reported for pure-rotational CARS systems. 24,[27][28][29]31,33,35 An interesting option to improve on this precision would be the application of an optical pulse stretcher. 47 In summary, the rovibrational CARS system presented here combines optimal single-shot precision at room and at flame temperatures.…”

mentioning

confidence: 99%

Thermometry for turbulent flames by coherent anti-Stokes Raman spectroscopy with simultaneous referencing to the modeless excitation profile

Veen

Roekaerts

2005

Appl. Opt.

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An optimal system for temperature measurements by coherent anti-Stokes Raman spectroscopy (CARS) in turbulent flames and flows is presented. In addition to a single-mode pump laser and a modeless dye laser, an echelle spectrometer with a cross disperser is used. This system permits simultaneous measurement of the N 2 CARS spectrum and the broadband dye laser profile. A procedure is developed to use software to transform this profile into the excitation profile by which the spectrum is referenced. Simultaneous shot-to-shot referencing is compared to sequential averaged referencing for data obtained in flat flames and in room air. At flame temperatures, the resultant 1.5% imprecision is limited by flame fluctuations, indicating that the system may have a single-shot imprecision below 1%. At room temperature, the 3.8% single-shot imprecision is of the same order as the best values reported for dualbroadband pure-rotational CARS. Using the unique shot-to-shot excitation profiles, simultaneous referencing eliminates systematic errors. At 2000 and 300 K, the 95% confidence intervals are estimated to be Ϯ20 and Ϯ10 K, respectively.

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“…Dual-broadband rotational CARS has been shown to be superior to single-broadband rotational CARS both from an experimental point of view and regarding the precision of the technique. 16 A CARS spectrum is modeled by the squared-modulus third-order susceptibility that has resonant contributions from each Raman resonance 3 r and also electronic nonresonant contributions 3 nr . The third-order susceptibility for rotational CARS 3 describing the coupling between the optical fields and the rotational levels of the molecules is in this case given for n species by…”

Section: Theorymentioning

confidence: 99%

Improved species concentration measurements using a species‐specific weighting procedure on rotational CARS spectra

Vestin

Afzelius

Bengtsson

2005

J Raman Spectroscopy

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Rotational coherent anti-Stokes Raman spectroscopy (CARS) is used for measurements of temperaturesand relative species concentrations. The evaluation of a rotational CARS spectrum is normally performed using a least-squares fitting algorithm to find the best-fit theoretical spectrum in a library of spectra calculated at different temperatures and relative concentrations. A general problem is that species with weak spectral features have a minor influence on the results in the standard evaluation procedure. A species-specific weighting (SSW) procedure enhancing the influence of weak spectral features in the spectral fitting algorithm has therefore been developed. The SSW procedure was tested on the evaluation of low concentrations of O 2 in mixtures with N 2 , and it is shown that both the accuracy and precision of single-shot spectra concentration measurements are improved by use of the SSW evaluation procedure. Also, a comparison with previously used weighting procedures shows that this approach is superior. The application of the technique to oxygen concentration measurements in the product gas of a fuel-lean flame is demonstrated. In addition, a test was made using the developed weighting procedure for thermometry, by applying spectral weighting to the rotational spectrum originating from the first thermally excited vibrational state. The precision of the temperature measurements was then slightly improved.

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Rotational CARS: a comparison of different techniques with emphasis on accuracy in temperature determination

Cited by 69 publications

References 48 publications

Influence of laser-mode statistics on noise in nonlinear-optical processes—application to single-shot broadband coherent anti-Stokes Raman scattering thermometry

Influence of laser-mode statistics on noise in nonlinear-optical processes—application to single-shot broadband coherent anti-Stokes Raman scattering thermometry

Thermometry for turbulent flames by coherent anti-Stokes Raman spectroscopy with simultaneous referencing to the modeless excitation profile

Improved species concentration measurements using a species‐specific weighting procedure on rotational CARS spectra

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