Spectroscopy coherent anti-Stokes Raman scattering, CARS

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... 

Several studies to determine the ablation mechanisms for picosecond laser ablation were focused on spectroscopy (coherent anti-Stokes Raman scattering (CARS), absorption, and ultrafast imaging) [108-113]. It has been shown that pulses in the picosecond range produce fast temperature jumps and solid-state shockwaves that are... 

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]. 

Lim, S. H., Caster, A., and Leone, S. R. 2005. Single pulse phase-control interferometric coherent anti-Stokes Raman scattering (CARS) spectroscopy. Phys. Rev. A 72 041803. 

Before melting and for some time after only the band at 625 cm of the AA [C4CiIm]+ cation was observed in the 600-630 cm i region. Gradually 603 cm i band due to the GA conformer became stronger. After about 10 min the AA/GA intensity ratio became constant. The interpretation [50] is that the rotational isomers do not interconvert momentarily at the molecular level. Most probably it involves a conversion of a larger local structure as a whole. The existence of such local structures of different rotamers has been found by optical heterodyne-detected Raman-induced Kerr-effect spectroscopy (OHD-RIKES) [82], Coherent anti-Stokes Raman scattering (CARS) [83],... 

In exemplarily flame measurements conducted at the LTT-Erlangen (Will et al., 1996), flame temperatures were determined by emission spectroscopy or coherent anti-Stokes Raman scattering (CARS) thermometry depending on the maximum soot concentration. Typical temperatures are in the range of 1800 K in the middle of the flames and up to 2100 K in the outer regions where the reactions take place. A typical measurement setup for two-dimensional LII investigations is shown in Figure 10. 

Here, E is the strength of the applied electric field (laser beam), a the polarizability and / and y the first and second hyper-polarizabilities, respectively. In the case of conventional Raman spectroscopy with CW lasers (E, 104 V cm-1), the contributions of the / and y terms to P are insignificant since a fi y. Their contributions become significant, however, when the sample is irradiated with extremely strong laser pulses ( 109 V cm-1) created by Q-switched ruby or Nd-YAG lasers (10-100 MW peak power). These giant pulses lead to novel spectroscopic phenomena such as the hyper-Raman effect, stimulated Raman effect, inverse Raman effect, coherent anti-Stokes Raman scattering (CARS), and photoacoustic Raman spectroscopy (PARS). Figure 3-40 shows transition schemes involved in each type of nonlinear Raman spectroscopy. (See Refs. 104-110.)... 

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. 

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). 

One of the most extensively used nonlinear processes for spectroscopy is coherent anti-Stokes Raman scattering (CARS). This is a four-wave mixing process of the form (Was = 2 ul — < s, where >l and >s are the laser and Stokes frequencies that are provided in the incident radiation and (Was is the anti-Stokes frequency that is generated... 

In addition to the mentioned Raman techniques, special methods are also used for the characterization of semiconductors, like the surface-enhanced Raman spectroscopy (SERS) and coherent anti-Stokes Raman scattering (CARS), Fourier transform (FT) Raman spectroscopy as well as Raman experiments, applying electric or magnetic fields. With the help of a Raman microscope surface scanning with a lateral resolution of a few micrometers is possible. By using a two-dimensional charge-coupled device (CCD) camera and a cylindrical lens for focusing the laser on the sample, lateral resolution can be also achieved besides the spectral resolution. 

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 (CARS) Spectroscopy/Microscopy... 

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