OSA's Digital Library

Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 10 — May. 20, 2013
  • pp: 12327–12339
« Show journal navigation

Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering temperature and concentration measurements using two different picosecond-duration probes

Sean P. Kearney, Daniel J. Scoglietti, and Christopher J. Kliewer  »View Author Affiliations


Optics Express, Vol. 21, Issue 10, pp. 12327-12339 (2013)
http://dx.doi.org/10.1364/OE.21.012327


View Full Text Article

Acrobat PDF (7649 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

A hybrid fs/ps pure-rotational CARS scheme is characterized in furnace-heated air at temperatures from 290 to 800 K. Impulsive femtosecond excitation is used to prepare a rotational Raman coherence that is probed with a ps-duration beam generated from an initially broadband fs pulse that is bandwidth limited using air-spaced Fabry-Perot etalons. CARS spectra are generated using 1.5- and 7.0-ps duration probe beams with corresponding coarse and narrow spectral widths. The spectra are fitted using a simple phenomenological model for both shot-averaged and single-shot measurements of temperature and oxygen mole fraction. Our single-shot temperature measurements exhibit high levels of precision and accuracy when the spectrally coarse 1.5-ps probe beam is used, demonstrating that high spectral resolution is not required for thermometry. An initial assessment of concentration measurements in air is also provided, with best results obtained using the higher resolution 7.0-ps probe. This systematic assessment of the hybrid CARS technique demonstrates its utility for practical application in low-temperature gas-phase systems.

© 2013 OSA

1. Introduction

Coherent anti-Stokes Raman scattering (CARS) is a powerful gas-phase diagnostic tool for probing of flames, high-speed flows, and plasmas. Typical CARS instruments for gas-phase diagnostics utilize Nd:YAG and dye laser systems with nanosecond-scale pulse durations and repetition rates on the order of 10 Hz [1

1. S. Roy, J. R. Gord, and A. K. Patnaik, “Recent advances in coherent anti-Stokes Raman scattering spectroscopy: fundamental developments and applications in reacting flows,” Pror. Energy Combust. Sci. 36(2), 280–306 (2010). [CrossRef]

]. These workhorse systems provide reliable thermometry, species, and pressure measurements [2

2. F. Beyrau, A. Datta, T. Seeger, and A. Leipertz, “Dual-pump CARS for the simultaneous detection of N2, O2 and CO in CH4 flames,” J. Raman Spectrosc. 33(11-12), 919–924 (2002). [CrossRef]

4

4. M. A. Woodmansee, R. P. Lucht, and J. C. Dutton, “Development of high-resolution N2 coherent anti-Stokes Raman scattering for measuring pressure, temperature, and density in high-speed gas flows,” Appl. Opt. 39(33), 6243–6256 (2000). [CrossRef] [PubMed]

]. Nevertheless, the 10-Hz repetition rate of nanosecond pulsed lasers does not permit time-resolved measurements in turbulent flows; measurements are impacted by uncertainty in nonresonant background and collision-broadened linewidths; and the broadband dye lasers employed as Stokes sources for single-shot data are plagued by chaotic mode noise and phase fluctuations [5

5. S. Kröll and D. Sandell, “Influence of laser mode statistics in nonlinear optical processes−application to single-shot broadband coherent anti-Stokes Raman scattering thermometry,” J. Opt. Soc. Am. B 5(9), 1910–1926 (1988). [CrossRef]

], which ultimately limits the precision of the measured thermochemical parameters.

Femtosecond-class laser systems are enabling new developments that overcome the above limitations in CARS of gas-phase systems. Commercial Ti:Sapphire amplifiers operate in the 1-10 kHz range, where the energy containing scales of many turbulent flows reside. Improved measurement precision is possible because near-transform-limited broadband femtosecond pulses exhibit minimal spectral-amplitude and spectral-phase noise, and are a superior alternative to chaotic broadband dye sources [6

6. R. P. Lucht, P. J. Kinnius, S. Roy, and J. R. Gord, “Theory of femtosecond coherent anti-Stokes Raman scattering spectroscopy of gas-phase transitions,” J. Chem. Phys. 127(4), 044316 (2007). [CrossRef] [PubMed]

, 7

7. D. R. Richardson, R. P. Lucht, W. D. Kulatilika, S. Roy, and J. R. Gord, “Theoretical modeling of single-laser-shot, chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering thermometry,” Appl. Phys. B 104(3), 699–714 (2011). [CrossRef]

]. This low-noise pump/Stokes preparation of the Raman coherence, when combined with the introduction of a time-delayed probe beam, permits effective time-gated elimination of nuisance nonresonant background signals. Probe delays as short as a few ps allow for collision-free measurements at modest pressures [1

1. S. Roy, J. R. Gord, and A. K. Patnaik, “Recent advances in coherent anti-Stokes Raman scattering spectroscopy: fundamental developments and applications in reacting flows,” Pror. Energy Combust. Sci. 36(2), 280–306 (2010). [CrossRef]

, 8

8. J. D. Miller, S. Roy, M. N. Slipchenko, J. R. Gord, and T. R. Meyer, “Single-shot gas-phase thermometry using pure-rotational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering,” Opt. Express 19(16), 15627–15640 (2011). [CrossRef] [PubMed]

]. At higher pressures, linewidth data can be obtained in situ by direct observation of the ps-scale decay of the Raman-resonant polarization [9

9. J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Time-domain measurement of high-pressure N2 and O2 self-broadened linewidths using hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering,” J. Chem. Phys. 135(20), 201104 (2011). [CrossRef] [PubMed]

, 10

10. Y. Gao, A. Bohlin, T. Seeger, P. E. Bengtsson, and C. J. Kliewer, “In situ determination of N2 broadening coefficients in flames for rotational CARS thermometry,” Proc. Combust. Inst. 34(2), 3637–3644 (2013). [CrossRef]

]. Practical combustion thermometry using femtosecond CARS of vibrational Raman resonances in N2 has been demonstrated using both bandwidth-limited [11

11. J. D. Miller, M. N. Slipchenko, T. R. Meyer, H. U. Stauffer, and J. R. Gord, “Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for high-speed gas-phase thermometry,” Opt. Lett. 35(14), 2430–2432 (2010). [CrossRef] [PubMed]

] and broadband temporally chirped [12

12. S. Roy, W. D. Kulatilaka, D. R. Richardson, R. P. Lucht, and J. R. Gord, “Gas-phase single-shot thermometry at 1 kHz using fs-CARS spectroscopy,” Opt. Lett. 34(24), 3857–3859 (2009). [CrossRef] [PubMed]

, 13

13. W. D. Kulatilaka, H. U. Stauffer, J. R. Gord, and S. Roy, “One-dimensional single-shot thermometry in flames using femtosecond-CARS line imaging,” Opt. Lett. 36(21), 4182–4184 (2011). [CrossRef] [PubMed]

] ps probes with single-laser-shot precision as good as 1% in some cases [7

7. D. R. Richardson, R. P. Lucht, W. D. Kulatilika, S. Roy, and J. R. Gord, “Theoretical modeling of single-laser-shot, chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering thermometry,” Appl. Phys. B 104(3), 699–714 (2011). [CrossRef]

].

When femtosecond pump and Stokes preparation is used, pure-rotational CARS (R-CARS) offers several distinct advantages to vibrational CARS (V-CARS) for gas-phase measurements. R-CARS is well-known to offer more precise thermometry at temperatures up to 1200 K, and the longer decay time of rotational Raman polarizations (~100 ps at 1 atm) makes time-gated suppression of nonresonant background more practical. R-CARS is also a more straightforward approach than V-CARS for simultaneous temperature and multiple-species detection in the femtosecond regime because most species of interest have rotational Raman frequencies on the order of a few hundred cm−1, which is well within the bandwidth of lasers with 50-100 fs pulses. Vibrational resonances for different species are often separated by 1000 cm−1 or more, rendering singe-shot multi-species detection using a single fs pump/Stokes combination less practical. These advantages have motivated several recent studies of R-CARS utilizing femtosecond pump/Stokes excitation with time-delayed bandwidth-limited ps probing [8

8. J. D. Miller, S. Roy, M. N. Slipchenko, J. R. Gord, and T. R. Meyer, “Single-shot gas-phase thermometry using pure-rotational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering,” Opt. Express 19(16), 15627–15640 (2011). [CrossRef] [PubMed]

, 9

9. J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Time-domain measurement of high-pressure N2 and O2 self-broadened linewidths using hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering,” J. Chem. Phys. 135(20), 201104 (2011). [CrossRef] [PubMed]

, 11

11. J. D. Miller, M. N. Slipchenko, T. R. Meyer, H. U. Stauffer, and J. R. Gord, “Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for high-speed gas-phase thermometry,” Opt. Lett. 35(14), 2430–2432 (2010). [CrossRef] [PubMed]

, 14

14. J. D. Miller, C. E. Dedic, S. Roy, J. R. Gord, and T. R. Meyer, “Interference-free gas-phase thermometry at elevated pressure using hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering,” Opt. Express 20(5), 5003–5010 (2012). [CrossRef] [PubMed]

, 15

15. H. U. Stauffer, J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering using a narrowband time-asymmetric probe pulse,” J. Chem. Phys. 136, 111101 (2012). [CrossRef] [PubMed]

]. These “hybrid” fs/ps R-CARS approaches have been demonstrated in pure N2 and O2 as a quantitative temperature diagnostic at both atmospheric and elevated pressures [8

8. J. D. Miller, S. Roy, M. N. Slipchenko, J. R. Gord, and T. R. Meyer, “Single-shot gas-phase thermometry using pure-rotational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering,” Opt. Express 19(16), 15627–15640 (2011). [CrossRef] [PubMed]

, 14

14. J. D. Miller, C. E. Dedic, S. Roy, J. R. Gord, and T. R. Meyer, “Interference-free gas-phase thermometry at elevated pressure using hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering,” Opt. Express 20(5), 5003–5010 (2012). [CrossRef] [PubMed]

, 15

15. H. U. Stauffer, J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering using a narrowband time-asymmetric probe pulse,” J. Chem. Phys. 136, 111101 (2012). [CrossRef] [PubMed]

], and for time-domain detection of self-broadened rotational linewidths [9

9. J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Time-domain measurement of high-pressure N2 and O2 self-broadened linewidths using hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering,” J. Chem. Phys. 135(20), 201104 (2011). [CrossRef] [PubMed]

]. Recent reports [16

16. J. D. Miller, T. R. Meyer, H. U. Stauffer, S. Roy, and J. R. Gord, “Latest developments on hybrid fs/ps CARS for combustion sensing,” in Laser Applications to Chemical Security and Environmental Analysis, Technical Digest (CD) (Optical Society of America, 2012), paper LW3B.2.

, 17

17. J. D. Miller, C. E. Dedic, T. R. Meyer, S. Roy, and J. R. Gord, “Rotational fs/ps CARS for in situ temperature and concentration measurements,” AIAA2012–1192, 50th Aerospace Sciences Meeting and New Horizons Forum, Nashville, TN, 6–9 Jan., 2012.

] of fs/ps R-CARS spectra in air are the first measurements with the technique in a gas mixture; qualitative changes in the spectra with temperature and the relative change in measured O2/N2 ratio with pressure were examined. In each of these hybrid R-CARS experiments, temporal locking of the preparation and probe pulses was achieved by using a single fs laser to provide all three pulses, and subsequently removing bandwidth from the probe using either a 4f pulse shaper [9

9. J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Time-domain measurement of high-pressure N2 and O2 self-broadened linewidths using hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering,” J. Chem. Phys. 135(20), 201104 (2011). [CrossRef] [PubMed]

, 18

18. J. D. Miller, M. N. Slipchenko, and T. R. Meyer, “Probe-pulse optimization for nonresonant suppression in hybrid fs/ps coherent anti-Stokes Raman scattering at high temperature,” Opt. Express 19(14), 13326–13333 (2011). [CrossRef] [PubMed]

] or a Fabry-Perot etalon [15

15. H. U. Stauffer, J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering using a narrowband time-asymmetric probe pulse,” J. Chem. Phys. 136, 111101 (2012). [CrossRef] [PubMed]

, 18

18. J. D. Miller, M. N. Slipchenko, and T. R. Meyer, “Probe-pulse optimization for nonresonant suppression in hybrid fs/ps coherent anti-Stokes Raman scattering at high temperature,” Opt. Express 19(14), 13326–13333 (2011). [CrossRef] [PubMed]

]. These bandwidth-carving approaches to ps probe-beam generation limit the available probe-beam energy and, ultimately the R-CARS signal strength. Recent work in our laboratory [19

19. S. P. Kearney and D. J. Scoglietti, “Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering at flame temperatures using a second-harmonic bandwidth-compressed probe,” Opt. Lett. 38(6), 833–835 (2013). [CrossRef] [PubMed]

] has focused on high-energy ps probe beams using sum-frequency generation of second-harmonic pulses from temporally chirped 800-nm beams. This new approach to probe-beam generation has extended hybrid R-CARS to flame temperatures, where temperature and quantitative O2/N2 measurements have been extracted from the high-temperature CARS spectra.

In this work, we perform a practical assessment of the diagnostic utility of an etalon-based hybrid fs/ps R-CARS setup of the type used in [15

15. H. U. Stauffer, J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering using a narrowband time-asymmetric probe pulse,” J. Chem. Phys. 136, 111101 (2012). [CrossRef] [PubMed]

], where the accuracy and precision of temperature and O2/N2 concentration measurements is systematically evaluated for temperatures from 290 to 800 K. The primary focus of the study is thermometry, although an assessment of O2/N2 ratio measurement in air over the full range of temperatures is also made. Two different etalon-generated probe beams are utilized: (1) a frequency-narrow (2.11 cm−1 FWHM) 7-ps-duration probe that permits resolution of individual rotational line structure in many cases; and (2) a second probe with 1.5-ps duration (5.3-cm−1 FWHM) that allows us to investigate the feasibility of measurements at coarser spectral resolution and a 3 × increase in probe-beam energy.

2. Experiment hardware and setup

The layout of our hybrid fs/ps rotational CARS system is shown in Fig. 1
Fig. 1 Essential elements of the fs/ps rotational CARS experiment.
. A “single-box” Ti:Sapphire amplifier (Spectra Physics Solstice) provided 3.1-mJ, 100-fs duration pulses at 1-kHz repetition rate. The amplifier output spectrum was centered near 800 nm, with a bandwidth of 180 cm−1 FWHM. The 800-nm beam was split into three parts to form pump, Stokes and probe beams. A half-waveplate and polarizer combination was used to limit thepump and Stokes beam energies to 40 and 53 μJ/pulse, respectively, in order to minimize the impact of stimulated Raman pumping [20

20. M. A. Woodmansee, R. P. Lucht, and J. C. Dutton, “Stark broadening and stimulated Raman pumping in high resolution N2 coherent anti-Stokes Raman scattering spectra,” AIAA J. 40(6), 1078–1086 (2002). [CrossRef]

], semi-permanent molecular alignment, and laser-induced ionization [21

21. A. Rouzeé, V. Renard, S. Guerin, O. Faucher, and B. Lavorel, “Suppression of plasma contributions in femtosecond degenerate four-wave mixing (fs-DFWM) at high intensity,” J. Raman Spectrosc. 38(8), 969–972 (2007). [CrossRef]

] associated with high preparation pulse energies. Picosecond-duration, frequency-narrow probe pulses were generated by inserting Fabry-Perot etalons into the probe-beam path, as first demonstrated for sum-frequency generation spectroscopy [22

22. A. Lagutchev, S. A. Hambir, and D. D. Dlott, “Nonresonant background suppression in broadband vibrational sum-frequency generation spectroscopy,” J. Phys. Chem. C 111(37), 13645–13647 (2007). [CrossRef]

], and more recently applied to hybrid fs/ps CARS [15

15. H. U. Stauffer, J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering using a narrowband time-asymmetric probe pulse,” J. Chem. Phys. 136, 111101 (2012). [CrossRef] [PubMed]

, 18

18. J. D. Miller, M. N. Slipchenko, and T. R. Meyer, “Probe-pulse optimization for nonresonant suppression in hybrid fs/ps coherent anti-Stokes Raman scattering at high temperature,” Opt. Express 19(14), 13326–13333 (2011). [CrossRef] [PubMed]

]. The available energy in the probe beam line was limited to 500 μJ/pulse by using a fixed-ratio beam splitter to minimize the risk of optical damage to the etalons. A spectrally narrow 7-ps duration probe was obtained using two etalons with free-spectral ranges (FRS) of 455 and 13 cm−1 in succession, while a coarser, 1.5-ps probe could be generated using the 455 cm−1 FSR etalon only. Probe-beam energies were 4 μJ/pulse for the double-etalon setup, and 12 μJ/pulse for the single-etalon arrangement. Each of the three lasers beams was routed to a time-of-flight delay line and then relayed to a 500-mm focal length beam-crossing lens in a carefully phase-matched folded BOXCARS [23

23. A. C. Eckbreth, “BOXCARS: Crossed-beam phase matched CARS generation in gases,” Appl. Phys. Lett. 32(7), 421–423 (1978). [CrossRef]

] geometry. Spatial isolation of the resulting CARS signal from the nearly frequency degenerate background laser radiation was obtained by careful alignment of apertures in the CARS collection optics path and by a tight 50-μm entrance slit on the 0.32-m imaging spectrometer used to detect the CARS signal with ~1 cm−1 instrument resolution. An electron-multiplying CCD camera (Andor Newton) was directly mated to the spectrometer to provide shot-averaged and single-shot detection at rates up to 250 Hz in our demonstration experiments.

Time-domain characterization of the probe pulse intensity profile was obtained by mechanically scanning the probe-beam delay through the ~100-fs nonresonant polarization induced by the pump and Stokes pulses in argon. Probe cross-correlation data are shown in Fig. 2
Fig. 2 Probe-beam cross-correlation data (left) and Fourier transform spectra (right).
for both the single-etalon (black lines) and double-etalon (blue lines) configurations. The power spectra (squared magnitude) of the Fourier transform of the cross-correlation data are also shown to provide an estimate of the frequency content, assuming that the probe pulses are transform limited. In the single-etalon configuration, the probe pulse exhibits the expectedbehavior reported by Stauffer et al. [15

15. H. U. Stauffer, J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering using a narrowband time-asymmetric probe pulse,” J. Chem. Phys. 136, 111101 (2012). [CrossRef] [PubMed]

], with a rapid ~300-fs rise from zero to maximum intensity followed by a nearly exponential decay with a ~1.5-ps time constant. The Fourier transform of the single-etalon cross-correlation data reveals a Lorentzian-like shape with 5.3 cm−1 FWHM bandwidth. Insertion of the 13 cm−1 FSR etalon further narrows the Fourier-transform bandwidth to ~2.1 cm−1, but introduces a complex shape to the probe. The double-etalon probe pulse exhibits the same rapid rise as in the single-etalon setup, but consists of a train of pulses, all with a rapid sub-picosecond rise and a ~2.5-ps exponential decay, with the pulse maxima separated by roughly 2.5 ps. This pulse train is similar to the behavior described by Lagutchev et al. [22

22. A. Lagutchev, S. A. Hambir, and D. D. Dlott, “Nonresonant background suppression in broadband vibrational sum-frequency generation spectroscopy,” J. Phys. Chem. C 111(37), 13645–13647 (2007). [CrossRef]

] for input pulses with coherence length less than the etalon gap. The resulting Fourier-transform spectrum reveals low-energy side lobes atop an otherwise Lorentzian lineshape.

3. Rotational CARS modeling

CARS spectra are calculated by adapting methods similar to those outlined in [8

8. J. D. Miller, S. Roy, M. N. Slipchenko, J. R. Gord, and T. R. Meyer, “Single-shot gas-phase thermometry using pure-rotational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering,” Opt. Express 19(16), 15627–15640 (2011). [CrossRef] [PubMed]

, 12

12. S. Roy, W. D. Kulatilaka, D. R. Richardson, R. P. Lucht, and J. R. Gord, “Gas-phase single-shot thermometry at 1 kHz using fs-CARS spectroscopy,” Opt. Lett. 34(24), 3857–3859 (2009). [CrossRef] [PubMed]

]. We consider the electric fields of all laser beams and the resulting CARS signal in the time domain. For the probe time delays of interest here, we need only consider the Raman-resonant part of the signal because the nonresonant signal is negligible when the probe pulse is introduced at sufficient time delay for the pump and Stokes pulses to decay to zero. Our calculation assumes transform-limited pump and Stokes pulses with infinite bandwidth, so that all Raman transitions are pumped with equal efficiencies. The experimental spectra are normalized by a nonresonant CARS spectrum recorded in argon at zero probe delay to account for finite laser bandwidth and departure of the preparation pulses from transform-limited behavior. Under these conditions, the time-dependent Raman-resonant polarization is given by,
χ(t)=kΔJ=±2WJJ'(k)exp[(iωJJ'(k)ΓJ(k))t].
(1)
In Eq. (1), the sum over k is taken over all rotationally resonant species (N2 and O2 here). The ωJJ´ are the rotational Raman frequencies taken from the Sandia CARSFT code [24

24. R. E. Palmer, “The CARSFT computer code for calculating coherent anti-Stokes Raman spectra: User and programmer information,” (Sandia National Laboratories, Livermore, CA, 1989).

] for a transition with initial angular-momentum quantum number J to state Jꞌ = J ± 2. The ωJJ’ are taken to be positive in sign for a Stokes transition with J=J+2 and negative in sign for an anti-Stokes transition withJ=J2, so that the two contributions oscillate with a phase difference of π. Collisional dephasing is modeled using J-dependent Raman linewidths, ΓJ. At the laboratory pressure (0.82 atm) and probe delays (τ < 5ps) in our experiments,exp(ΓJt)1, so that the Raman linewidths have negligible impact on our results. The WJJ’ in Eq. (1) are weighting functions, which are given by,
WJJ'(k)=Xkγk2(NJ'(k)NJ(k))bJJFJ(k).
(2)
In Eq. (2), the NJ are the temperature-dependent rotational Boltzmann fractions for the J and Jstates; Xk and γk2 are the mole fraction and polarizability anisotropy of species k, respectively; and bJJare the Placzek-Teller coefficients,
bJ,J+2=3(J+1)(J+2)2(2J+3)(2J+1),
(3)
and
bJ,J2=3(J1)J2(2J1)(2J+1).
(4)
The FJ(k) are the Herman-Wallis factors [25

25. A. Bohlin, P. E. Bengtsson, and M. Marrocco, “On the sensitivity of rotational N2 CARS thermometry to the Herman-Wallis factor,” J. Raman Spectrosc. 42(10), 1843–1847 (2011). [CrossRef]

], which account for the effect of vibration-rotation interaction. At the temperatures investigated in this work (T < 800 K), these J-dependent corrections have little effect on the results, but have been retained for completeness.

At the low, 290-800 K, temperatures investigated, we only consider rotational transitions in the ground vibrational level. Values of γk2are referenced to N2. Drake and Rosenblatt [26

26. M. C. Drake and G. M. Rosenblatt, “Rotational Raman scattering from premixed and diffusion flames,” Combust. Flame 33, 179–196 (1978). [CrossRef]

] tabulate values of γO22/γN22that range from 2.26 to 2.64. We have set γO22/γN22 = 2.370 in this work. This value was determined to achieve reasonable agreement between fitted O2/N2 concentration ratios and the known value of [O2]/[N2] = 0.2683 when fitting room-temperature R-CARS spectra obtained with the 7-ps probe.

With knowledge of the Raman-resonant polarization, χ, the CARS electric field at a probe-beam delay of τ is calculated in the time domain from,
ECARS(tτ)=Epr(tτ)exp[iωo(tτ)]×χ(t),
(5)
where ωo is the probe-beam center (carrier) frequency and Epr is the assumed transform-limited probe electric-field amplitude, taken from the square root of the cross correlation measurements shown in Fig. 2. The CARS spectrum is then expressed in the frequency domain by the squared amplitude of the Fourier transform of the field given by Eq. (5). This computed CARS spectrum is then convolved with a 1-cm−1 Gaussian slit function and interpolated onto the experimental grid for comparison to the measured spectra.

The experimental spectra are background subtracted for stray light and normalized by nonresonant CARS spectra from argon. The resulting processed spectra are normalized to unit maximum and fitted using a nonlinear least-squares algorithm where the temperature and O2/N2 ratio are fitting parameters along with wavenumber axis shifting and stretching parameters and an intensity offset. The probe pulse delay is permitted to vary within a ± 0.5-ps window to account for uncertainty in the measured delay. Fitted probe delays exhibit standard deviations of 3.5% of the mean value for single-shot spectra across a wide range of temperatures when using the 1.5-ps probe at 3.4-ps nominal delay. Standard deviation in the fitted delay is 1.9% of the mean when using the 7-ps probe at 800 K and 2.8-ps nominal delay. Sensitivity of the fitted temperatures and O2/N2 ratio to these observed levels of probe delay uncertainty is determined to be less than 1%.

4. Results and discussion

4.1 Time-dependent behavior of air spectra at room temperature

A spectrogram constructed from hybrid fs/ps R-CARS spectra recorded with probe delays scanned from 0 to 20 ps in room-temperature air (292 K), and using the 1.5-ps duration probe, is shown in Fig. 3
Fig. 3 Room-temperature specta for air in the single-etalon probe configuration with a 1.5-ps/5.3-cm−1 probe beam.
. Experimental data are the average of 100 laser shots at each probe delay, and are shown on the top of the Figure with the theoretical prediction shown below. For reference, the temporal evolution of the rotational coherence, χ(t) given by Eq. (1), is provided below the spectrograms. Only the imaginary part of Raman-resonant χ is plotted, as the real part is zero. The visual comparison between the measured and calculated spectrograms is excellent; the simple model of Eqs. (1)(5) predicts the complex behavior of the rotational Raman transients in a quantitative manner. Introduction of a second gas into the mixture results in spectrograms which are less regular than those reported by Stauffer et al. [15

15. H. U. Stauffer, J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering using a narrowband time-asymmetric probe pulse,” J. Chem. Phys. 136, 111101 (2012). [CrossRef] [PubMed]

] for pure N2. The character of the spectrum exhibits distinct changes when the fast rising edge of the probe pulse crosses the recurrence peaks in χ(t), with peaks in the spectrum shifting their position and even disappearing at some probe delays. This behavior arises from the complex beating of the rotational polarization with the probe electric field, as well as interference between contributions from O2 and ortho/para N2 to the total rotational wavepacket.

The quantitative agreement of our model and room-temperature experiments is demonstrated by least-squares fits to the measured spectra at the three probe delays indicated by the vertical, dashed lines on the experimental spectrogram of Fig. 3. The fitted temperatures range from 285.5 K to 291.5 K, within 2.2% of the measured room temperature. Fitted O2/N2 ratios are within 3.5% of the expected value of 0.268 for air for probe delays of τ = 1.6 ps and 3.4 ps, with a 9% inaccuracy at τ = 4.2 ps, where a sudden and abrupt change in the spectrogram occurs as the probe rising edge is aligned with a recurrence peak, and the lowest quality fits were achieved. Increased sensitivity of the fitted spectra to probe delay may be expected when the probe is coincident with time-domain recurrence features. This sensitivity seems to impact the measured temperature and concentration, which may be an artifact of the multi-parameter fitting routine or small changes in relative beam path lengths resulting from environmental effects.

Similar room-air spectrograms for the 7-ps duration probe beam obtained in the double-etalon configuration are shown in Fig. 4
Fig. 4 Room-temperature specta for air in the double-etalon probe configuration with a 7-ps/2.1-cm−1 probe beam.
. This high-resolution probe pulse provides better-resolved O2 and N2 contributions to the spectrum. The longer time duration of the higher spectral resolution probe results in the simultaneous probing of a greater number of recurrence features, but significant time-dependent changes to the spectrum are still observed. Fitted temperatures in air are within 2.3% of the monitored room value with O2/N2 ratios within less than 1% of the known air composition.

4.2 Furnace-heated air: shot-averaged spectra

CARS spectra were recorded for air in a tube furnace for temperatures from 292 K to 798 K for both single- and double-etalon probe beam-line configurations, and with the probe beam delay fixed in each case. The spectra were averaged for 100 to 1,000 laser shots to optimize signal-to-noise ratio in the data. Higher loss of probe beam energy when twoetalons were used resulted in lower single-shot signal-to-noise ratio. Shot-averaging provides a means to compare the performance of the technique for the two probe beams used. Measured furnace spectra obtained using the 1.5-ps duration, 5.3-cm−1 linewidth probe are shown along with theoretical fits for 6 different temperatures in Fig. 5
Fig. 5 Fits to CARS spectra obtained in tube-furnace-heated air in the single-etalon probe configuration with a 1.5-ps/5.3-cm−1 probe beam at a nominal probe delay of 3.5 ps.
. These spectra were recorded with the probe delay fixed near τ = 3.5 ps, and the fitted delays are generally within 40 fs of a mean fitted value of τ = 3.42 ps. The best-fit temperature, O2/N2 ratio and probe delay are shown on each plot along with temperature indicated by a thermocouple that was placed into the furnace gas after the conclusion of the CARS experiments. Fitted temperatures are accurate to within ± 2% of thermocouple measurements, which is comparable to the accuracy reported for nanosecond rotational CARS by Seeger and Leipertz [27

27. T. Seeger and A. Leipertz, “Experimental comparison of single-shot broadband vibrational and dual-broadband pure rotational coherent anti-Stokes Raman scattering in hot air,” Appl. Opt. 35(15), 2665–2671 (1996). [CrossRef] [PubMed]

]. Fitted O2/N2 ratios range from + 8.4% to −10% of the known value, and a systematic decrease in measured O2/N2 with increasing temperature is observed.

Fits to the temperature-dependent air spectra for the 7-ps duration, 2.1-cm−1 linewidth probe at a fixed delay near τ = 2.8 ps are shown in Fig. 6
Fig. 6 Fits to CARS spectra obtained in tube-furnace-heated air in the double-etalon probe configuration with a 7-ps/2.1-cm−1 probe beam at a nominal probe delay of 2.8 ps.
. Similar quality fits are seen at this finer probe resolution, with the fitted temperature generally within 1-3% of thermocouple readings. CARS-measured temperatures are higher than the thermocouple data for T < 600 K and lower at higher temperatures. Measured O2/N2 ratio is within 2% of the known value, which is superior to the results obtained with the 1.5-ps probe, albeit with a similar systematic trend toward lower O2/N2 observed with increasing temperature.

4.3 Furnace-heated air: single-laser-shot data

Randomly selected single-laser-shot spectra are shown in Fig. 7
Fig. 7 Fits to single-laser-shot CARS spectra at several temperatures in tube-furnace-heated air: 1.5-ps/5.3-cm−1 probe (top and middle), and 7.0-ps/2.1-cm−1 probe (bottom).
. Spectra recorded using the 1.5-ps probe are shown in plots a-d, with spectra taken using the 7-ps probe provided in plots e and f. The 3 × increase in probe-beam energy available in the 1.5-ps probe provides increased signal-to-noise ratio relative to the higher resolution 7-ps probe. Temperature histograms were constructed from ensembles of 500 to 1000 single-shot measurements at each furnace setting, and plotted for the same conditions as the spectra of Fig. 7 in Fig. 8
Fig. 8 Temperature histograms obtained from fits to single-laser-shot fs/ps rotational CARS spectra.
. The results of our single-shot data campaign are summarized in Table 1

Table 1. Summary of fitting results for single-laser-shot spectra.

table-icon
View This Table
, where six furnace settings are reported for spectra obtained with the 1.5-ps probe, and two for the finer resolution 7-ps probe. The precision in the single-shot temperature data is quantified by the ratio, σT/T¯,where σT is the standard deviation of the histogram data and T¯ is the corresponding mean. Based upon this metric, the precision in our single-shot temperature data is outstanding at the higher signal levels afforded by the 1.5-ps probe beam. Values of σT/T¯range from 0.8% at room temperature to 1.9% at 773 K, with the metric hovering just above 1% for all temperatures in between. This level of temperature-measurement precision compares very favorably to values reported for nanosecond rotational CARS, where “typical” values of 3-4% are common fromroom conditions to flame temperatures [27

27. T. Seeger and A. Leipertz, “Experimental comparison of single-shot broadband vibrational and dual-broadband pure rotational coherent anti-Stokes Raman scattering in hot air,” Appl. Opt. 35(15), 2665–2671 (1996). [CrossRef] [PubMed]

]. Temperature-measurement precision is degraded to ± 3.7 and ± 2.6% at furnace settings of 521 and 773 K, respectively, when the more frequency narrow 7-ps probe is used. We presume that this is a result of the above-mentioned decreased signal-to-noise in the spectra shown in Figs. 7(e) and 7(f), and not due to the intrinsic nature of the high-resolution spectra. Single-shot O2/N2 statistics in air are additionally compiled in Table 1. The mean values range from O2/N2 = 0.25 to 0.275, or −7.3% to + 2.5% of the true value in air. When using the 1.5-ps probe, the standard deviation of the O2/N2 measurement ranges from 1.1 to 4.3% of the mean, with degraded levels of precision observed with the 7-ps probe.

We believe that the reason for the observed improvement in temperature-measurement precision relative to nanosecond CARS is a result of the low-noise pump/Stokes driving offered by the nearly transform-limited femtosecond preparation pulses. This results in very low levels of spectral amplitude and phase noise when compared to nanosecond broadband dye lasers. This high-quality preparation of the Raman coherence yields very repeatable spectral envelopes, as illustrated in Fig. 9
Fig. 9 One thousand single-laser-shot spectra normalized to the peak CARS intensity at temperatures of 292 K and 491 K. The spectra highlight the low level of noise due to near-transform-limited pump/Stokes preparation.
, where 1000 single-shot spectra are overlaid on a single set of axes at furnace settings of T = 292 K and 473 K. The spectra have been normalized to unit maximum to remove shot-to-shot intensity fluctuations while preserving the spectral shape. It is seen that the spectral envelopes are essentially identical over all 1000 laser shots in each case. The shot-to-shot repeatability is particularly striking at T = 292 K, where signal levels are highest.

5. Summary and conclusion

The results of our study are summarized graphically in Fig. 10
Fig. 10 Summary of fitted temperatures and O2/N2 ratios.
, where fitted temperature and O2/N2 ratio from both shot-averaged and single-laser-shot spectra are plotted against the furnace thermocouple reading. Data points for single-shot results represent the sample mean, while error bars (where visible) represent a single standard deviation of the single-shot results. Temperature-measurement accuracy was generally within 2.5%. Best thermometry results were obtained using the 1.5-ps/5.3 cm−1 probe, where CARS photon yields were higher as a a result of the increase in retained probe bandwidth and energy. Using this low-resolution probe, a single-shot temperature measurement precision of 1% was demonstrated fortemperatures from 290 to 700 K and 1.9% near 800 K. Temperature accuracy was retained in shot-averaged spectra when a 7-ps/2.1 cm−1 probe was used, with some degradation in the single-shot precision that we presume is due to lower CARS photon yields associated with this lower energy probe. O2/N2 concentration ratios were most accurate when the low-energy, high-resolution 7-ps probe was utilized, with some systematic trend toward lower O2/N2 with increasing temperature for both probe resolutions. Single-shot precision in O2/N2 was 1-4% for the 1.5-ps probe and 4-8.6% for the 7-ps probe.

This study demonstrates the utility of the hybrid fs/ps CARS approach for practical, high-precision and background-free diagnostics in a gas mixture. Use of etalons and other bandwidth-limiting pulse shapers limits the available picosecond probe-beam energy, providing a practical limit on probe linewidth and on the highest temperature measureable with these bandwidth-carving approaches. The coarse resolution in the 1.5-ps probe beam does not appear to limit the potential of the technique for thermometry, but with some decreased accuracy in the concentration measurements reported here. Even coarser probe-beam resolutions may still provide adequate thermometry, and an upper limit on probe bandwidth has yet to be assessed. We are currently working on methods to increase the energy content in frequency-narrow probe beams [19

19. S. P. Kearney and D. J. Scoglietti, “Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering at flame temperatures using a second-harmonic bandwidth-compressed probe,” Opt. Lett. 38(6), 833–835 (2013). [CrossRef] [PubMed]

] and extend the technique to flame temperatures with a more systematic evaluation of concentration measurement capability.

Acknowledgments

The authors recognize Terry Meyer and Joe Miller of Iowa State University for productive discussions on fs/ps CARS approaches. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.

References and links

1.

S. Roy, J. R. Gord, and A. K. Patnaik, “Recent advances in coherent anti-Stokes Raman scattering spectroscopy: fundamental developments and applications in reacting flows,” Pror. Energy Combust. Sci. 36(2), 280–306 (2010). [CrossRef]

2.

F. Beyrau, A. Datta, T. Seeger, and A. Leipertz, “Dual-pump CARS for the simultaneous detection of N2, O2 and CO in CH4 flames,” J. Raman Spectrosc. 33(11-12), 919–924 (2002). [CrossRef]

3.

F. Beyrau, T. Seeger, A. Malarski, and A. Leipertz, “Determination of temperatures and fuel/air ratios in an ethene-air flame by dual-pump CARS,” J. Raman Spectrosc. 34(12), 946–951 (2003). [CrossRef]

4.

M. A. Woodmansee, R. P. Lucht, and J. C. Dutton, “Development of high-resolution N2 coherent anti-Stokes Raman scattering for measuring pressure, temperature, and density in high-speed gas flows,” Appl. Opt. 39(33), 6243–6256 (2000). [CrossRef] [PubMed]

5.

S. Kröll and D. Sandell, “Influence of laser mode statistics in nonlinear optical processes−application to single-shot broadband coherent anti-Stokes Raman scattering thermometry,” J. Opt. Soc. Am. B 5(9), 1910–1926 (1988). [CrossRef]

6.

R. P. Lucht, P. J. Kinnius, S. Roy, and J. R. Gord, “Theory of femtosecond coherent anti-Stokes Raman scattering spectroscopy of gas-phase transitions,” J. Chem. Phys. 127(4), 044316 (2007). [CrossRef] [PubMed]

7.

D. R. Richardson, R. P. Lucht, W. D. Kulatilika, S. Roy, and J. R. Gord, “Theoretical modeling of single-laser-shot, chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering thermometry,” Appl. Phys. B 104(3), 699–714 (2011). [CrossRef]

8.

J. D. Miller, S. Roy, M. N. Slipchenko, J. R. Gord, and T. R. Meyer, “Single-shot gas-phase thermometry using pure-rotational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering,” Opt. Express 19(16), 15627–15640 (2011). [CrossRef] [PubMed]

9.

J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Time-domain measurement of high-pressure N2 and O2 self-broadened linewidths using hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering,” J. Chem. Phys. 135(20), 201104 (2011). [CrossRef] [PubMed]

10.

Y. Gao, A. Bohlin, T. Seeger, P. E. Bengtsson, and C. J. Kliewer, “In situ determination of N2 broadening coefficients in flames for rotational CARS thermometry,” Proc. Combust. Inst. 34(2), 3637–3644 (2013). [CrossRef]

11.

J. D. Miller, M. N. Slipchenko, T. R. Meyer, H. U. Stauffer, and J. R. Gord, “Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for high-speed gas-phase thermometry,” Opt. Lett. 35(14), 2430–2432 (2010). [CrossRef] [PubMed]

12.

S. Roy, W. D. Kulatilaka, D. R. Richardson, R. P. Lucht, and J. R. Gord, “Gas-phase single-shot thermometry at 1 kHz using fs-CARS spectroscopy,” Opt. Lett. 34(24), 3857–3859 (2009). [CrossRef] [PubMed]

13.

W. D. Kulatilaka, H. U. Stauffer, J. R. Gord, and S. Roy, “One-dimensional single-shot thermometry in flames using femtosecond-CARS line imaging,” Opt. Lett. 36(21), 4182–4184 (2011). [CrossRef] [PubMed]

14.

J. D. Miller, C. E. Dedic, S. Roy, J. R. Gord, and T. R. Meyer, “Interference-free gas-phase thermometry at elevated pressure using hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering,” Opt. Express 20(5), 5003–5010 (2012). [CrossRef] [PubMed]

15.

H. U. Stauffer, J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering using a narrowband time-asymmetric probe pulse,” J. Chem. Phys. 136, 111101 (2012). [CrossRef] [PubMed]

16.

J. D. Miller, T. R. Meyer, H. U. Stauffer, S. Roy, and J. R. Gord, “Latest developments on hybrid fs/ps CARS for combustion sensing,” in Laser Applications to Chemical Security and Environmental Analysis, Technical Digest (CD) (Optical Society of America, 2012), paper LW3B.2.

17.

J. D. Miller, C. E. Dedic, T. R. Meyer, S. Roy, and J. R. Gord, “Rotational fs/ps CARS for in situ temperature and concentration measurements,” AIAA2012–1192, 50th Aerospace Sciences Meeting and New Horizons Forum, Nashville, TN, 6–9 Jan., 2012.

18.

J. D. Miller, M. N. Slipchenko, and T. R. Meyer, “Probe-pulse optimization for nonresonant suppression in hybrid fs/ps coherent anti-Stokes Raman scattering at high temperature,” Opt. Express 19(14), 13326–13333 (2011). [CrossRef] [PubMed]

19.

S. P. Kearney and D. J. Scoglietti, “Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering at flame temperatures using a second-harmonic bandwidth-compressed probe,” Opt. Lett. 38(6), 833–835 (2013). [CrossRef] [PubMed]

20.

M. A. Woodmansee, R. P. Lucht, and J. C. Dutton, “Stark broadening and stimulated Raman pumping in high resolution N2 coherent anti-Stokes Raman scattering spectra,” AIAA J. 40(6), 1078–1086 (2002). [CrossRef]

21.

A. Rouzeé, V. Renard, S. Guerin, O. Faucher, and B. Lavorel, “Suppression of plasma contributions in femtosecond degenerate four-wave mixing (fs-DFWM) at high intensity,” J. Raman Spectrosc. 38(8), 969–972 (2007). [CrossRef]

22.

A. Lagutchev, S. A. Hambir, and D. D. Dlott, “Nonresonant background suppression in broadband vibrational sum-frequency generation spectroscopy,” J. Phys. Chem. C 111(37), 13645–13647 (2007). [CrossRef]

23.

A. C. Eckbreth, “BOXCARS: Crossed-beam phase matched CARS generation in gases,” Appl. Phys. Lett. 32(7), 421–423 (1978). [CrossRef]

24.

R. E. Palmer, “The CARSFT computer code for calculating coherent anti-Stokes Raman spectra: User and programmer information,” (Sandia National Laboratories, Livermore, CA, 1989).

25.

A. Bohlin, P. E. Bengtsson, and M. Marrocco, “On the sensitivity of rotational N2 CARS thermometry to the Herman-Wallis factor,” J. Raman Spectrosc. 42(10), 1843–1847 (2011). [CrossRef]

26.

M. C. Drake and G. M. Rosenblatt, “Rotational Raman scattering from premixed and diffusion flames,” Combust. Flame 33, 179–196 (1978). [CrossRef]

27.

T. Seeger and A. Leipertz, “Experimental comparison of single-shot broadband vibrational and dual-broadband pure rotational coherent anti-Stokes Raman scattering in hot air,” Appl. Opt. 35(15), 2665–2671 (1996). [CrossRef] [PubMed]

OCIS Codes
(120.1740) Instrumentation, measurement, and metrology : Combustion diagnostics
(120.6780) Instrumentation, measurement, and metrology : Temperature
(190.4380) Nonlinear optics : Nonlinear optics, four-wave mixing
(300.6230) Spectroscopy : Spectroscopy, coherent anti-Stokes Raman scattering
(320.2250) Ultrafast optics : Femtosecond phenomena

ToC Category:
Instrumentation, Measurement, and Metrology

History
Original Manuscript: February 25, 2013
Revised Manuscript: May 3, 2013
Manuscript Accepted: May 8, 2013
Published: May 13, 2013

Citation
Sean P. Kearney, Daniel J. Scoglietti, and Christopher J. Kliewer, "Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering temperature and concentration measurements using two different picosecond-duration probes," Opt. Express 21, 12327-12339 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-10-12327


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. S. Roy, J. R. Gord, and A. K. Patnaik, “Recent advances in coherent anti-Stokes Raman scattering spectroscopy: fundamental developments and applications in reacting flows,” Pror. Energy Combust. Sci.36(2), 280–306 (2010). [CrossRef]
  2. F. Beyrau, A. Datta, T. Seeger, and A. Leipertz, “Dual-pump CARS for the simultaneous detection of N2, O2 and CO in CH4 flames,” J. Raman Spectrosc.33(11-12), 919–924 (2002). [CrossRef]
  3. F. Beyrau, T. Seeger, A. Malarski, and A. Leipertz, “Determination of temperatures and fuel/air ratios in an ethene-air flame by dual-pump CARS,” J. Raman Spectrosc.34(12), 946–951 (2003). [CrossRef]
  4. M. A. Woodmansee, R. P. Lucht, and J. C. Dutton, “Development of high-resolution N2 coherent anti-Stokes Raman scattering for measuring pressure, temperature, and density in high-speed gas flows,” Appl. Opt.39(33), 6243–6256 (2000). [CrossRef] [PubMed]
  5. S. Kröll and D. Sandell, “Influence of laser mode statistics in nonlinear optical processes−application to single-shot broadband coherent anti-Stokes Raman scattering thermometry,” J. Opt. Soc. Am. B5(9), 1910–1926 (1988). [CrossRef]
  6. R. P. Lucht, P. J. Kinnius, S. Roy, and J. R. Gord, “Theory of femtosecond coherent anti-Stokes Raman scattering spectroscopy of gas-phase transitions,” J. Chem. Phys.127(4), 044316 (2007). [CrossRef] [PubMed]
  7. D. R. Richardson, R. P. Lucht, W. D. Kulatilika, S. Roy, and J. R. Gord, “Theoretical modeling of single-laser-shot, chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering thermometry,” Appl. Phys. B104(3), 699–714 (2011). [CrossRef]
  8. J. D. Miller, S. Roy, M. N. Slipchenko, J. R. Gord, and T. R. Meyer, “Single-shot gas-phase thermometry using pure-rotational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering,” Opt. Express19(16), 15627–15640 (2011). [CrossRef] [PubMed]
  9. J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Time-domain measurement of high-pressure N2 and O2 self-broadened linewidths using hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering,” J. Chem. Phys.135(20), 201104 (2011). [CrossRef] [PubMed]
  10. Y. Gao, A. Bohlin, T. Seeger, P. E. Bengtsson, and C. J. Kliewer, “In situ determination of N2 broadening coefficients in flames for rotational CARS thermometry,” Proc. Combust. Inst.34(2), 3637–3644 (2013). [CrossRef]
  11. J. D. Miller, M. N. Slipchenko, T. R. Meyer, H. U. Stauffer, and J. R. Gord, “Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering for high-speed gas-phase thermometry,” Opt. Lett.35(14), 2430–2432 (2010). [CrossRef] [PubMed]
  12. S. Roy, W. D. Kulatilaka, D. R. Richardson, R. P. Lucht, and J. R. Gord, “Gas-phase single-shot thermometry at 1 kHz using fs-CARS spectroscopy,” Opt. Lett.34(24), 3857–3859 (2009). [CrossRef] [PubMed]
  13. W. D. Kulatilaka, H. U. Stauffer, J. R. Gord, and S. Roy, “One-dimensional single-shot thermometry in flames using femtosecond-CARS line imaging,” Opt. Lett.36(21), 4182–4184 (2011). [CrossRef] [PubMed]
  14. J. D. Miller, C. E. Dedic, S. Roy, J. R. Gord, and T. R. Meyer, “Interference-free gas-phase thermometry at elevated pressure using hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering,” Opt. Express20(5), 5003–5010 (2012). [CrossRef] [PubMed]
  15. H. U. Stauffer, J. D. Miller, S. Roy, J. R. Gord, and T. R. Meyer, “Communication: Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering using a narrowband time-asymmetric probe pulse,” J. Chem. Phys.136, 111101 (2012). [CrossRef] [PubMed]
  16. J. D. Miller, T. R. Meyer, H. U. Stauffer, S. Roy, and J. R. Gord, “Latest developments on hybrid fs/ps CARS for combustion sensing,” in Laser Applications to Chemical Security and Environmental Analysis, Technical Digest (CD) (Optical Society of America, 2012), paper LW3B.2.
  17. J. D. Miller, C. E. Dedic, T. R. Meyer, S. Roy, and J. R. Gord, “Rotational fs/ps CARS for in situ temperature and concentration measurements,” AIAA2012–1192, 50th Aerospace Sciences Meeting and New Horizons Forum, Nashville, TN, 6–9 Jan., 2012.
  18. J. D. Miller, M. N. Slipchenko, and T. R. Meyer, “Probe-pulse optimization for nonresonant suppression in hybrid fs/ps coherent anti-Stokes Raman scattering at high temperature,” Opt. Express19(14), 13326–13333 (2011). [CrossRef] [PubMed]
  19. S. P. Kearney and D. J. Scoglietti, “Hybrid femtosecond/picosecond rotational coherent anti-Stokes Raman scattering at flame temperatures using a second-harmonic bandwidth-compressed probe,” Opt. Lett.38(6), 833–835 (2013). [CrossRef] [PubMed]
  20. M. A. Woodmansee, R. P. Lucht, and J. C. Dutton, “Stark broadening and stimulated Raman pumping in high resolution N2 coherent anti-Stokes Raman scattering spectra,” AIAA J.40(6), 1078–1086 (2002). [CrossRef]
  21. A. Rouzeé, V. Renard, S. Guerin, O. Faucher, and B. Lavorel, “Suppression of plasma contributions in femtosecond degenerate four-wave mixing (fs-DFWM) at high intensity,” J. Raman Spectrosc.38(8), 969–972 (2007). [CrossRef]
  22. A. Lagutchev, S. A. Hambir, and D. D. Dlott, “Nonresonant background suppression in broadband vibrational sum-frequency generation spectroscopy,” J. Phys. Chem. C111(37), 13645–13647 (2007). [CrossRef]
  23. A. C. Eckbreth, “BOXCARS: Crossed-beam phase matched CARS generation in gases,” Appl. Phys. Lett.32(7), 421–423 (1978). [CrossRef]
  24. R. E. Palmer, “The CARSFT computer code for calculating coherent anti-Stokes Raman spectra: User and programmer information,” (Sandia National Laboratories, Livermore, CA, 1989).
  25. A. Bohlin, P. E. Bengtsson, and M. Marrocco, “On the sensitivity of rotational N2 CARS thermometry to the Herman-Wallis factor,” J. Raman Spectrosc.42(10), 1843–1847 (2011). [CrossRef]
  26. M. C. Drake and G. M. Rosenblatt, “Rotational Raman scattering from premixed and diffusion flames,” Combust. Flame33, 179–196 (1978). [CrossRef]
  27. T. Seeger and A. Leipertz, “Experimental comparison of single-shot broadband vibrational and dual-broadband pure rotational coherent anti-Stokes Raman scattering in hot air,” Appl. Opt.35(15), 2665–2671 (1996). [CrossRef] [PubMed]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited