Stokes scattering from

The reason why the spacings are equal, and not the 1-0, 2-1, 3-2,... anharmonic intervals, is explained in Figure 9.21. The laser radiation of wavenumber Vg takes benzene molecules into the virtual state Fj from which they may drop down to the v = level. The resulting Stokes scattering is, as mentioned above, extremely intense in the forward direction with about 50 per cent of the incident radiation scattered at a wavenumber of Vg — Vj. This radiation is sufficiently intense to take other molecules into the virtual state V2, resulting in intense scattering at Vg — 2vj, and so on. 

The quantum mechanical view of Raman scatering sees a radiation field hvo inducing a transition from a lower level A to a level n. If vnlc is the transition frequency, then the inelastically scattered light has frequency v0 — v t. That is, the molecule removes energy hv k from an incident photon. This process corresponds to Stokes scattering. Alternatively, a molecule under-... 

It is important from a practical viewpoint to predict the shear viscosity of mixtures from those of pure melts. For alkali nitrate melts, a linear dependence has been found between the reorientational line width obtained by Raman measurements and the ratio of temperature divided by shear viscosity.For NO3 ions, the depolarized Raman scattering from 1050cm" total stretching vibrational mode (Al) has a contribution to the line width L, which is caused by the reorientational relaxation time of the Csv axis of this ion. The Stokes-Einstein-Debye(SED) relation establishes a relation between the shear viscosity r of a melt and the relaxation time for the reorientation of a particle immersed in it ... 

A small fraction of the molecules are in vibrationally excited states. Raman scattering from vibrationally excited molecules leaves the molecule in the ground state. The scattered photon appears at higher energy, as shown in Figure lb. This anti-Stokes-shifted Raman spectrum is always weaker than the Stokes-shifted spectrum, but at room temperature it is strong enough to be useful for vibrational frequencies less than about 1500 cm 1. The Stokes and anti-Stokes spectra contain the same frequency information. 

S.-X. Qian, J. B. Snow, and R. K. Chang, Coherent Raman mixing and coherent anti-Stokes Raman scattering from individual micrometer-sized droplets, Opt. Lett. 10, 499-501 (1985). 

Field enhancement factors observed in Raman scattering from molecules adsorbed on nanosurfaces are even larger. The intensity of Stokes component in Raman scattering is proportional to the square of dipole momentum on that frequency [61] ... 

Figure 7.15 Fringe structure of the anti-Stokes scattering observed by the interference of two Raman excitations. Open circles are observed data and solid lines are sine functions fitted to the observed data, (a) The delay is scanned around 10 ps. (b) The delay Tjj g is scanned around 500 ps. In both cases, the probe pulse is irradiated at 1 ns after the first excitation. The intensity is normalized by the signal intensity when only the single IRE pulse is irradiated. Reproduced with permission from Ref. [43]. Copyright 2013 by the American Physical Society.

Figure 10.1. Comparison of normal (top) and surface-enhanced (bottom) Raman scattering. The top panel shows the conversion of incident laser light of intensity /(vl) into Stokes scattered light /NRS, which is proportional to the Raman cross section and the number of target molecules N in the probed volume. In the bottom panel

SERS is considered an inelastic scattering effect because the signals of interest are Stokes-shifted from the incident excitation. This means that the field-enhancement... 

The overall combustor/optical layout is shown in Fig. 3, which illustrates temperature measurement by the Stokes/anti-Stokes method. Typical results for temperature pdf s at four radial positions (2, 7) near the centerline to near the flame boundary - and at an axial distance 50 fuel-tip diameters downstream of the fuel line tip are shown in Fig. 4. The shaded parts of the pdf contours (from 300 to 800°K), which increase in area near the flame boundary, correspond substantially to scattering from ambient temperature air, and therefore provide a measure of flow intermittency. The upper limit of these bins was chosen to be 800°K because the accuracy possible for the Stokes/anti-Stokes temperature measurement method degrades rapidly at temperatures below roughly that value (2,2) Thus, treating the fluctuation temperature data for T < 800 K in any greater detail was unwarranted. 

Figure 3. Calculated band profiles of Stokes vibrational Raman scattering from Nt at 2000 K assuming a triangular slit function with FWHM = 5.0 cm 1. The bottom curve includes the isotropic part of the Q-branch only. The top curve is a more exact calculation including O- and S-branch scattering, the anisotropic part of the Q-branch and line-strength corrections owing to centrifugal distortion. The base lines have been shifted vertically for clarity.

Block the laser beam or spectrometer entrance slit and adjust the spectrometer to an anti-Stokes shift of 1000 cm Caution Exposure of the sensitive phototube to the intense Rayleigh scattering line can seriously damage the detector. Scan the anti-Stokes spectrum from 1000 to 150 cm in the parallel polarization configuration and, using appropriate sensitivity expansion, j measure the ratio of anti-Stokes to Stokes peak heights for each band. 

Dynamic Light Scattering. The hydrodynamic radius, Rh, is defined as the Stokes radius from the mutual diffusion coefficient at infinite dilution (Do)... 

Fig. 3.4 (a) Representative spectrum from Anti-stokes/Stokes scattering experiment for the investigation of particle heating, (b) Comparison of the calculated AS/S ratio for the integrals of the peaks at —568 and 570 cm respectively. Error bars show one single standard deviation of the integrals of 10 spectra... 

---