Raman excitation

We also tried measurements to demonstrate that hot spots make significant contributions to surface enhanced Raman scattering [34]. For this purpose, the sample of nanoparticie assembly was doped with Raman active molecules by a spincoating method, and near-field excited Raman scattering from the sample was recorded. We adopted Rhodamine 6G dye as a Raman active material, which is... 

Figure 3.10 (a) Topography of the sample, (b), (c) Near-field excited Raman spectra at dimers 1 and 2, respectively,taken attwodifferentincident polarizations. The peaks marked with are unassigned, (d) Near-field two-photon excitation images of dimers 1 and 2. (e) Near-field Raman excitation images of dimers 1 and 2 obtained for... 

Figure 7 shows a sequence of Raman spectra from sample D with different excitation wavelengths. Figure 7a, b, and c corresponds to 514 nm, 325 nm, and 244 nm, respectively. Compared with the spectrum of 514-nm excitation, the 325-nm excited Raman spectrum exhibits a clear peak at 1332 cm and the remarkable enhancement of the... 

The TED and XRD patterns revealed that the deposit is not amorphous carbon but nanocrystalline diamond. Nonetheless, the 514-nm excited Raman spectra do not exhibit a clear diamond peak at 1332 cm though the peak due to the sp -bonded carbon network appears at 1150 cm The Raman cross section of the sp -bonded carbon network with visible excitation is resonantly enhanced [43, 48-50]. It consequently makes the 1332 cm diamond peak overlap with the peaks due to sp -bonded carbon. 

The 244-nm excited Raman spectra of t-aC films exhibit the appearance of the peak at 1150 cm and the increase in the intensity proportional to the amount of sp bonding in the films [50, 51]. However, the diamond peak at 1332 cm is enhanced in this study because the deposit obtained is not amorphous carbon but nanocrystalline diamond. The peak at --1150 cm is probably disappearing because of the striking enhancement of the diamond peak at 1332 cm T... 

Figure 21 488 nm excitation Raman spectra of PANI exposed to elevated temperatures for... 

Then, there are model Hamiltonians. Effectively a model Hamiltonian includes only some effects, in order to focus on those effects. It is generally simpler than the true full Coulomb Hamiltonian, but is made that way to focus on a particular aspect, be it magnetization, Coulomb interaction, diffusion, phase transitions, etc. A good example is the set of model Hamiltonians used to describe the IETS experiment and (more generally) vibronic and vibrational effects in transport junctions. Special models are also used to deal with chirality in molecular transport junctions [42, 43], as well as optical excitation, Raman excitation [44], spin dynamics, and other aspects that go well beyond the simple transport phenomena associated with these systems. 

The effect of tetrachlorate ions on water structure has been investigated with laser Raman spectra by Walrafen 213), and Lippin-cott etal. 212a) studied poly water configurations. There are numerous other investigations of laser-excited Raman spectra, the discussion of which would demand a special review article 2i3b-f). 

Another area of laser use applied to expl materials involves its employment to excite Raman spectra for studies of crystal structure, lattice dynamics, phase transitions and vibrational mode frequencies. Compds studied include T1N3 (Refs 10, 17 23), NaN3 (Ref 18), KN3 and RbN3 (Ref 4), NH4N3 (Ref 7), BaN3 (Refs 5, 8 24), LA (Ref 9), HMX (Ref 25), RDX (Ref 11) and Amm perchlorate (Ref 26)... 

Iqbal et al (Ref 56) measured the transmission infrared and laser excited Raman spectra of poly crystalline RDX in the range of 40 to 4000/cm. To aid assignments in the spectral region of 400 to 4000/cm, the spectra of two types of N15-labeled samples and the soln spectra in different solvents were also recorded. From these data it was possible to assign many of the observed bands to intramolecular modes of the RDX molecule. The Raman-active lattice modes also were resolved and found to be comparable to the lattice mode frequencies in solid cyclohexane... 

Raman spectroscopy has been widely used to study the composition and molecular structure of polymers [100, 101, 102, 103, 104]. Assessment of conformation, tacticity, orientation, chain bonds and crystallinity bands are quite well established. However, some difficulties have been found when analysing Raman data since the band intensities depend upon several factors, such as laser power and sample and instrument alignment, which are not dependent on the sample chemical properties. Raman spectra may show a non-linear base line to fluorescence (or incandescence in near infrared excited Raman spectra). Fluorescence is a strong light emission, which interferes with or totally swaps the weak Raman signal. It is therefore necessary to remove the effects of these variables. Several methods and mathematical artefacts have been used in order to remove the effects of fluorescence on the spectra [105, 106, 107]. 

Before the invention of lasers in 1960 (Maiman), radiation emitted by the mercury arc, especially at 435.8 and 404.7 nm, has been u.sed for exciting Raman spectra (Brandmiiller and Moser, 1962). Today, most types of lasers ( continuous wave (cw) and pulsed, gas, solid state, semiconductor, etc.), with emission lines from the UV to the NIR region, are used as radiation sources for the excitation of Raman spectra. Especially argon ion lasers with lines at 488 and 515 nm are presently employed. NIR Raman spectra are excited mainly with a neodymium doped yttrium-aluminum garnet laser (Nd YAG), emitting at 1064 nm. 

In the case of relatively high absorption coefficients, as in NIR-excited Raman spectroscopy, coarse powders should be investigated with a back-scattering (180°) multiple reflection arrangement. 

Consequently, in order to perform quantitative analyses by NIR excited Raman spectroscopy, it is necessary to consider the absorption of the sample or the solvent. 

In this case study, we have carried out further investigation into the structure of VO, supported on alumina under both oxidized (dehydrated) and reduced environments using both UV- (244 nm) and visible- (488 nm) excited Raman spectroscopy. Special attention has been directed towards the structure of supported VO at extremely low surface density (down to 0.01 Vnm ). 

Lord, R. C. and Yu, N. Y. (1970a). Laser-excited Raman Spectroscopy of biomolecules. I. Native lysozyme and its constituent amino acids. J. Mol Biol, 50, 509-24. [224]... 

Shifted excitation Raman difference spectroscopy (SERDS) One way to remove the fluorescent background in traditional Raman Spectroscopy is to take advantage of the shift response of the Raman Effect to excitation wavelength shifts. In SERDS, two spectra of a sample are acquired with slightly different excitation wavelengths, and are then subtracted to estimate the Raman spectrum of a sample. This difference will impact the Raman spectra where the entire spectrum will shift in energy by the amount of excitation shift [16]. 

McCain MX, Willett RM, Brady DJ (2008) Multi-excitation Raman spectroscopy technique for fluorescence rejection. Opt Express 16(15) 10975-10991... 

The excitation Raman profiles for adsorbed dyes are generally different from those for the dyes in solution, and from that of normal scatterers exhibiting the SERS effect. 

A photon with frequency v0 is absorbed by a Raman-active molecule that is at the time of interaction already in an excited vibrational state. If the excess energy of the excited Raman-active mode is released, the molecule returns to the basic vibrational state, and the resulting frequency of scattered light is v0 + vm. This Raman frequency is called Anti-Stokes frequency. 

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