Femtosecond coherent anti-Stokes Raman scattering measurement of gas temperatures from frequency-spread dephasing of the Raman coherence

Raman spectroscopy is an increasingly popular technique in many areas including biology and medicine.It is based on Raman scattering, a phenomenon in which incident photons lose or gain energy via interactions with vibrating molecules in a sample. These energy shifts can be used to obtain information regarding molecular composition of the sample with very high accuracy. Applications of Raman spectroscopy in the life sciences have included quantification of biomolecules, hyperspectral molecular imaging of cells and tissue, medical diagnosis, and others. This review briefly presents the physical origin of Raman scattering explaining the key classical and quantum mechanical concepts. Variations of the Raman effect will also be considered, including resonance, coherent, and enhanced Raman scattering. We discuss the molecular origins of prominent bands often found in the Raman spectra of biological samples. Finally, we examine several variations of Raman spectroscopy techniques in practice, looking at their applications, strengths, and challenges. This review is intended to be a starting resource for scientists new to Raman spectroscopy, providing theoretical background and practical examples as the foundation for further study and exploration.

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“…This relationship has been used to remotely estimate the temperature of samples at very low temperatures [35][36][37].…”

Section: Stokes and Anti-stokes Raman Scattering Intensitiesmentioning

confidence: 99%

Raman spectroscopy: techniques and applications in the life sciences

Shipp¹,

Sinjab²,

Notingher³

2017

Adv. Opt. Photon.

270

189

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“…Instead of frequency-domain detection of the molecular distribution, the timedependent molecular response is resolved by temporally delaying the CARS probe from the initial Raman resonance induced by the pump and Stokes pulses [1,[20][21][22][23][24][25][26]. By utilizing the slope of the initial decay of the CARS signal due to frequency-spread dephasing, it is possible to extract gas-phase temperatures without interferences from collisional energy transfer [23][24][25][26]. Initial measurements utilized a slow-scan mechanical delay stage to probe the rovibrational Raman coherence at various time delays relative to the initial impulsive excitation [23,24].…”

Section: Introductionmentioning

confidence: 99%

Single-shot gas-phase thermometry using pure-rotational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering

Miller¹,

Roy²,

Slipchenko³

et al. 2011

Opt. Express

Self Cite

105

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High-repetition-rate, single-laser-shot measurements are important for the investigation of unsteady flows where temperature and species concentrations can vary significantly. Here, we demonstrate singleshot, purerotational, hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps RCARS) thermometry based on a kHz-rate fs laser source. Interferences that can affect nanosecond (ns) and ps CARS, such as nonresonant background and collisional dephasing, are eliminated by selecting an appropriate time delay between the 100-fs pump/Stokes pulses and the pulse-shaped 8.4-ps probe. A time-and frequencydomain theoretical model is introduced to account for rotational-level dependent collisional dephasing and indicates that the optimal probe-pulse time delay is 13.5 ps to 30 ps. This time delay allows for uncorrected best-fit N 2 -RCARS temperature measurements with ~1% accuracy. Hence, the hybrid fs/ps RCARS approach can be performed with kHz-rate laser sources while avoiding corrections that can be difficult to predict in unsteady flows. KeywordsFriedrich-Alexander University Erlangen-Nürnberg, aerodynamics, probes, Raman scattering, Raman spectroscopy, temperature measurement, thermometers, dephasing, femtoseconds, frequency domains, Fs laser, gasphase, high repetition rate, laser sources, species concentration, equipment design, optics and photonics, Fourier analysis Abstract: High-repetition-rate, single-laser-shot measurements are important for the investigation of unsteady flows where temperature and species concentrations can vary significantly. Here, we demonstrate singleshot, pure-rotational, hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps RCARS) thermometry based on a kHz-rate fs laser source. Interferences that can affect nanosecond (ns) and ps CARS, such as nonresonant background and collisional dephasing, are eliminated by selecting an appropriate time delay between the 100-fs pump/Stokes pulses and the pulse-shaped 8.4-ps probe. A time-and frequency-domain theoretical model is introduced to account for rotational-level dependent collisional dephasing and indicates that the optimal probe-pulse time delay is 13.5 ps to 30 ps. This time delay allows for uncorrected best-fit N 2 -RCARS temperature measurements with ~1% accuracy. Hence, the hybrid fs/ps RCARS approach can be performed with kHz-rate laser sources while avoiding corrections that can be difficult to predict in unsteady flows.

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“…The latter decay has been used in gas thermometry, since its rate depends on the initial rotational population distribution [11][12][13][14][15][16]. On a longer time scale, the dephasing is followed by a series of full and fractional revivals of the ro-vibrational wave packet, analyzed both theoretically [7,8] and experimentally [5,6].…”

Section: Introductionmentioning

confidence: 99%

“…As in gas thermometry, the decay of vibrational coherence on a short time scale (i.e. first few picoseconds) has been used for detecting molecular concentrations [12,14]. In contrast, we exploit the long-term evolution of the vibrational coherence, which contains time intervals during which the background molecules are "silent" whereas the minority molecules are not (i.e.…”

Section: Introductionmentioning

confidence: 99%

Coherent anti-Stokes Raman spectroscopy in the presence of strong resonant signal from background molecules

Bitter¹,

Milner²

2013

Opt. Lett.

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Optical spectroscopy with broadband femtosecond laser pulses often involves simultaneous excitation of multiple molecular species with close resonance frequencies. Interpreting the collective optical response from molecular mixtures typically requires Fourier analysis of the detected timeresolved signal. We propose an alternative method of separating coherent optical responses from two molecular species with neighboring excitation resonances (here, vibrational modes of oxygen and carbon dioxide). We utilize ro-vibrational coupling as a mechanism of suppressing the strong vibrational response from the dominating molecular species (O2). Coherent ro-vibrational dynamics lead to long "silence windows" of zero signal from oxygen molecules. In these silence windows, the detected signal stems solely from the minority species (CO2) enabling background-free detection and characterization of the O2/CO2 mixing ratio. In comparison to a Fourier analysis, our technique does not require femtosecond time resolution or time-delay scanning.

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Femtosecond coherent anti-Stokes Raman scattering measurement of gas temperatures from frequency-spread dephasing of the Raman coherence

Cited by 144 publications

References 12 publications

Raman spectroscopy: techniques and applications in the life sciences

Raman spectroscopy: techniques and applications in the life sciences

Single-shot gas-phase thermometry using pure-rotational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering

Coherent anti-Stokes Raman spectroscopy in the presence of strong resonant signal from background molecules

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