Second coherent vibrational spectroscopy

Hirose, Y, Yui, H. and Sawada, T. (2005) Second harmonic generation-based coherent vibrational spectroscopy for a liquid interface under the nonresonant pump condition. J. Phys. Chem. B, 109, 13063-13066. 

SHG-VGS Second-harmonic-generation coherent vibrational spectroscopy... 

Fig. 12.8 In coherent Raman spectroscopy, a beam of electromagnetic radiation with frequency Vp and wavevector kp, and a second beam with frequency Vj and wavevector are focused on the sample. Radiation emitted with frequency v = 2Vp — Vj and wavevector kf= 2kp — k, is collected. Stokes Raman transitions of the ground electronic state are stimulated when Vp — v, = v, where hv is a vibrational mode of the sample anti-Stokes transitions are stimulated when Vp — v = —v... 

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. 

A technique which combines the high sensitivity of resonant laser ionization methods with the advantages of nonlinear coherent Raman spectroscopy is called IDSRS (ionization detected stimulated Raman spectroscopy). The excitation process, illustrated in Figure 5, can be briefly described as a two-step photoexcitation process followed by ion/electron detection. In the first step two intense narrow-band lasers (ct L, 0) ) are used to vibrationally excite the molecule via the stimulated Raman process. The excited molecules are then selectively ionized in a second step via a two- or multiphoton process. If there are intermediate resonant states involved (as state c in Figure 5), the method is called REMPI (resonance enhanced multi-photon ionization)-detected stimulated Raman spectroscopy. The technique allows an increase in sensitivity of over three orders of magnitude because ions can be detected with much higher sensitivity than photons. 

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. 

Following the initial proposal, fifth-order time domain Raman spectroscopy received considerable attention both theoretically (11-20) and experimentally (21-32). For the case of intermolecular motions, the majority of the experimental efforts have involved probing the intermolecular modes of liquid CS2, a standard system in nonresonant Raman spectroscopy due to its very large polarizability and the wealth of available experimental results. Experimental efforts to probe intramolecular vibrations are fewer in number, with the only published example probing modes of liquid CH3C1 and CCU (24). It was quickly realized that, owing to the direct transfer of the first vibrational coherence to the second, the experiment offered substantially more information than had initially been... 

Most of the vibrational and rotational spectra obtained before the second world war were measured using Raman methods. Interest in Raman then declined as infrared and microwave absorption instrumentation developed, but the introduction of visible lasers in the early 1960s has led to dramatic renaissance in Raman spectroscopy. As well as decreasing the acquisition time and increasing the sensitivity of conventional Raman spectra by orders of magnitude, the high power and coherence properties of laser radiation has spawned a host of new nonlinear Raman spectroscopies, some of which can be performed without a... 

The first term in this Taylor expansion around qo has no coordinate dependence and is time independent The second term is Unear in coordinate dependence and corresponds to the signal measured in third-order Raman experiments. To generate a fifth-order Raman signal the third term is necessary if a single harmonic mode, qj, is assumed, signal generation requires a two-quantum coherence to be created by one of the interactions. Subsequent to this realization it was proposed [28] that the spectroscopy also probes any anharmonicity in the vibrational potential, which corresponds to the inclusion of a cubic anharmonicity term ... 

---