Search results for "Coherent anti-Stokes Raman spectroscopy"
showing 10 items of 48 documents
Time-Resolved Coherent Anti-Stokes Raman Scattering of Graphene: Dephasing Dynamics of Optical Phonon.
2017
We report dynamics of the G-mode in graphene probed with time-resolved coherent anti-Stokes Raman scattering measurements. By applying BOXCARS excitation geometry with three different excitation wavelengths, various nonlinear processes can be selectively detected due to energy and momentum conservation and temporal sequence of the pulses. The Raman signal due to resonant coherent excitation of the G-mode shows exponential decay with lifetime of ∼325 ± 50 fs. This decay time is shorter than expected based on the line width of the G-mode in the Raman spectrum. We propose that the unexpectedly short dephasing time is a result of dynamic variation of nonadiabatic coupling of the photoexcited el…
Excitonic model for second-order resonant Raman scattering.
1994
A theoretical model for second-order resonant Raman scattering is presented. The effect of Coulomb interaction between electrons and holes is fully taken into account in the framework of the effective-mass approximation. By introducing discrete and continuous excitonic intermediate states in the Raman process, an explicit expression for the Raman scattering efficiency is given for long-range Fr\"ohlich electron-phonon interaction. The model developed can be used to evaluate Raman profiles around the resonant region. A closed-form expression for all matrix elements of the exciton-phonon interaction is obtained once the Coulomb problem for the relative electron-hole motion is separated in sph…
Electronic and acoustic-phonon inter-Landau-level Raman scattering in GaAs/AlxGa1−xAs multiple quantum wells
1995
We present an experimental study of inter-Landau-level excitations in undoped GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As multiple quantum wells in high magnetic fields by means of Raman scattering. The experiments were performed in Faraday backscattering geometry with the field along the growth axis, using circularly polarized light for resonant excitation of low-index magneto-optical transitions between Landau levels. We observe two types of peaks. One of them, present in both Stokes and anti-Stokes regions at a constant Raman shift, corresponds to the electron cyclotron energy. We attribute it to electronic Raman scattering from a quasistationa…
Electric-field-induced Raman scattering in GaAs: Franz-Keldysh oscillations
1995
We have studied the influence of strong electric fields on the Raman scattering intensity from LO phonons in GaAs (100) at room temperature using laser excitation energies above the fundamental ${\mathit{E}}_{0}$ gap. Striking oscillations are found in the scattering intensity for configurations where either the deformation potential or Fr\"ohlich electron-phonon interaction contribute. The oscillations in the deformation-potential-mediated scattering intensity can be related to Franz-Keldysh oscillations derived from the ${\mathit{E}}_{0}$ gap, whereas a more complicated mechanism has to be invoked for processes where Fr\"ohlich interaction is responsible.
Inelastic neutron and low-frequency Raman scattering in a niobium-phosphate glass for Raman gain applications
2011
Abstract We present measurements of the vibrational spectrum of a binary niobium-phosphate glass in the THz frequency range using inelastic neutron and Raman scattering. The spectra of these glasses show a low-frequency enhancement of the vibrational density of states (“boson peak”). Using a recently developed theory of vibrational excitations in disordered solids we are able to reconcile the measured neutron and Raman spectra using fluctuating elastic and Pockels constants as a model concept. As the spontaneous Raman susceptibility is a key parameter for Raman amplification our results suggest a significant gain profile for application of niobium-phosphate glasses in Raman amplifiers.
Variability of the Si-O-Si angle in amorphous-SiO2 probed by electron paramagnetic resonance and Raman spectroscopy
2009
We report an experimental investigation by electron paramagnetic resonance (EPR) and Raman spectroscopy on a variety of amorphous silicon dioxide materials. Our study by EPR have permitted us to point out that the splitting of the primary hyperfine doublet of the Eγ′ center shows a relevant sample-to-sample variability, changing from ∼41.8 to ∼42.6 mT in the set of materials we considered. The parallel study by Raman spectroscopy has enabled us to state that this variability is attributable to the different Si-O-Si angle characterizing the matrices of the different materials. © 2009 Elsevier B.V. All rights reserved.
Raman Scattering Applied to Materials Science
2015
Abstract One of the most powerful techniques to extract physical and chemical information of a material is the light scattering. Opposite to x-ray scattering for instance, where an average of the sample properties is obtained, Raman scattering is a local probe which can be used to detect inhomogeneities, local strain, lack of crystallinity, anharmonicities or information on the electronic structure by means of resonant Raman scattering. In this work, we will analyze the main contributions of Raman scattering in Materials Sciences. After a brief introduction of the technique and the equipment needed for the physical measurements, we will give practical examples of Raman scattering measuremen…
Collisional shifting and broadening coefficients for the rovibrational anisotropic S(J) lines of nitrogen studied by inverse Raman spectroscopy
1996
0377-0486; Line shifting and broadening coefficients of the anisotropic S(J) lines (v = 0, J --> v = 1, J + 2) of the nitrogen molecule were measured at room temperature using high-resolution stimulated Raman spectroscopy. A rotational quantum number dependence of the S(J) line shifts was observed. In order to avoid an asymmetry of experimental origin, a suitable theoretical profile was fitted to the experimental lineshapes. This study allows the testing of the theoretical methods for calculating the line broadening coefficients in anisotropic Raman scattering, which have already been used in the analysis of infrared absorption data. The behaviour of the modified sum rule and the RPA (rando…
Accurate spectroscopic constants of nitrogen determined from stimulated Raman spectra of the fundamental and first hot bands
1990
Nitrogen spectra of the Q-branch of the fundamental and the first hot bands were recorde with a high-resolution stimulated Raman spectrometer at atmospheric pressure and ca. 1300 K. The absolute frequencies of the Raman lines were measured with high accuracy, leading to a refinement of spectroscopic constants. A temperature estimation was also performed from the Raman intensities.
Raman spectroscopy of the high- and low-spin states of the spin crossover complex Fe(phen)2(NCS)2: an initial approach to estimation of vibrational c…
2000
Abstract Raman spectra of the spin-crossover complex Fe(phen)2(NCS)2 in the solid state have been recorded at 785 nm as a function of temperature to investigate the contribution of intramolecular vibrations to the entropy change, ΔS, associated with spin crossover. The modes of major interest for estimating the contribution lie in the range 100–500 cm−1, where the largest qualitative changes with temperature in the Raman spectra were observed. Analysis of these data, with the working assumption of an average frequency in this range as representative of the 15 distortion modes of an idealised FeN6 octahedron, leads to the conclusion that the intramolecular vibrations represent a primary cont…