Vibrational spectroscopies coherent anti-Stokes-Raman scattering

In order to realize molecular-vibration spectroscopy, coherent anti-Stokes Raman scattering (CARS) spectroscopy is employed, which is one of the most widely used nonlinear Raman spectroscopes (Shen 1984). CARS spectroscopy uses three incident fields including a pump field (< i), a Stokes field (0)2, 0 2 < 1) and a probe field (<0/ = <0i), and induces a nonlinear polarization at the frequency of <03 = 2<0i - <02 which is given in a scalar form by... 

Among approaches in vibrational spectroscopy are differential and time-resolved IR and Raman spectroscopy, coherent anti-Stokes Raman scattering (CARS), Fourier transform infrared spectroscopy (FT-IR) multidimensional IR and RR spectroscopy, two-dimensional infrared echo and Raman echo [56], and ultrafast time-resolved spontaneous and coherent Raman spectroscopy the structure and dynamics of photogenerated transient spedes [50, 57]. 

In this chapter we will first discuss coherent anti-Stokes Raman scattering (CARS) of simple liquids and binary mixtures for the determination of vibrational dephasing and correlation times. The time constants represent detailed information on the intermolecular interactions in the liquid phase. In the second section we consider strongly associated liquids and summarize the results of time-resolved IR spectroscopy (see, e.g., Ref. 17) on the dynamics of monomeric and associated alcohols as well as isotopic water mixtures. 

Time resolved coherent anti-Stokes Raman spectroscopy of condensed matter has been recently extended to the femtosecond domain allowing direct and detailed studies of the fast relaxation processes of molecular vibrations in liquids. The vibrational phase relaxation (dephasing) is a fundamental physical process of molecular dynamics and has attracted considerable attention. Both experimental and theoretical studies have been performed to understand microscopic processes of vibrational dephasing. Developments in ultrafast coherent spectroscopy enables one now to obtain direct time-domain information on molecular vibrational dynamics. Femtosecond time-resolved coherent anti-Stokes Raman scattering measuring systems have been constructed (see Sec. 3.6.2.2.3) with an overall time resolution of less than 100 fs (10 s). Pioneering work has been per-... 

Nonlinear vibrational spectroscopy provides accessibility to a range of vibrational information that is hardly obtainable from conventional linear spectroscopy. Recent progress in the pulsed laser technology has made the nonlinear Raman effect a widely applicable analytical method. In this chapter, two types of nonlinear Raman techniques, hyper-Raman scattering (HRS) spectroscopy and time-frequency two-dimensional broadband coherent anti-Stokes Raman scattering (2D-CARS) spectroscopy, are applied for characterizing carbon nanomaterials. The former is used as an alternative for IR spectroscopy. The latter is useful for studying dynamics of nanomaterials. 

Ichimura T, Hayazawa N, Hashimoto M, Inouye Y, Kawata S (2004) Application of tip-enhanced microscopy for nonlinear Raman spectroscopy. Appl Phys Lett 84 1768 Ichimura T, Hayazawa N, Hashimoto M, Inouye Y, Kawata S (2004) Tip-enhanced coherent anti-stokes raman scattering for vibrational nanoimaging. Phys Rev Lett 92 220801 Tanaka S, Maeda Y, Cai L, Tabata H, Kawai T (2001) Application of tip-enhanced microscopy for nonlinear Raman spectroscopy. Jpn J Appl Phys 40 4217 Watanabe H, Ishida Y, Hayazawa N, Inouye Y, Kawata S (2004) Tip-enhanced near-field Raman analysis of tip-pressurized adenine molecule. Phys Rev B 69 155418 Yano T, Verma P, Saito Y, Ichimura T, Kawata S (2009) Pressure-assisted tip-enhanced Raman imaging at a resolution of a few nanometres. Nature Photon 3 473 Yano T, Inouye Y, Kawata S (2006) Nanoscale uniaxial pressure effect of a carbon nanotube bundle on tip-enhanced near-field Raman spectra. Nano Lett 6 1269 Downes A, Salter D, Elfick A (2006) Heating effects in tip-enhanced optical microscopy. Opt Exp 14 5216... 

Coherent anti-Stokes Raman scattering (CARS) provides a promising method for examining vibrationally excited intermediates formed in isomerization reactions of polyatomic molecules. The technique may permit kinetic spectroscopy of single vibrational levels during fast reactions (Luther and Wieters). 

The laser-based techniques currently being used and developed include vibrational Raman scattering, coherent anti-Stokes Raman scattering (CARS), Rayleigh scattering, laser-induced fluorescence, and planar laser-induced fluorescence (PLIF). This is an active research field at various research establishments. Laser-induced fluorescence spectroscopy has been used to measure several combustion intermediates, for example, CH, C2, HCH, OH, NO, NO2, HNO, CO, halogenated hydrocarbons, and polycyclic aromatic hydrocarbons. 

Resonances betwen Raman active molecular vibrations and rotations and the difference frequency combination 0)1 —0)2 can also occur. When the four-wave mixing process 2o)i — 0)2 or o)i+o)2 — 0)2 is used with these resonances it is termed coherent anti-Stokes Raman scattering (CARS). The resonant enhancement that occurs in the generated intensity as the pump frequencies are tuned through the two-photon difference-frequency resonance forms the basis of CARS spectroscopy (see Section IV.A). 

F. Moya, S.A.J. Druet, J.P. Taran Rotation-vibration spectroscopy of gases by coherent anti-Stokes Raman scattering Application to concentration and temperature nieasmements. In Laser Spectroscopyy ed. by S. Haroche, J.C. Pebay Peyroula, T.W. H sch, S.E. Harris (Springer, Berlin, Heidelberg 1975)... 

Recently, the femtosecond time-resolved spectroscopy has been developed and many interesting publications can now be found in the literature. On the other hand, reports on time-resolved vibrational spectroscopy on semiconductor nanostructures, especially on quantum wires and quantum dots, are rather rare until now. This is mainly caused by the poor signal-to-noise ratio in these systems as well as by the fast decay rates of the optical phonons, which afford very fast and sensitive detection systems. Because of these difficulties, the direct detection of the temporal evolution of Raman signals by Raman spectroscopy or CARS (coherent anti-Stokes Raman scattering) [266,268,271-273] is often not used, but indirect methods, in which the vibrational dynamics can be observed as a decaying modulation of the differential transmission in pump/probe experiments or of the transient four-wave mixing (TFWM) signal are used. 

Section 2.1 with those in Section 2.2 for one- and two-photon absorption and dichroism and for magnetic circular dichroism. In the second part of the section, attention will be focused on some vibrational spectroscopies, namely vibrational circular dichroism (VCD), ROA, and coherent anti-Stokes Raman scattering (CARS), which have become increasingly popular in the last few years. 

Coherent Anti-Stokes—Raman Scattering Ab initio calculations of nonlinear vibrational spectroscopies is a field that is very much in its infancy, and we will therefore not dwell much on this topic here, Umiting ourselves to a recent example from our own research group, namely the foiu -wave mixing processes that lead to CARS [290]. 

The inelastic processes - spontaneous Raman scattering (usually simply called Raman scattering), nonlinear Raman processes, and fluorescence - permit determination of species densities as well as temperature, and also allow one, in principle, to determine the temperature for particular species whether or not in thermal equilibrium. In Table II, we categorize these inelastic processes by the type of the information that they yield, and indicate the types of combustion sources that can be probed as well as an estimate of the status of the method. The work that we concentrate upon here is that indicated in these first two categories, viz., temperature and major species densities determined from vibrational Raman scattering data. The other methods - fluorescence and nonlinear processes such as coherent anti-Stokes Raman spectroscopy - are discussed in detail elsewhere (5). 

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