Search results for "Stokes"
showing 10 items of 242 documents
Transverse chemical interface detection with coherent anti-Stokes Raman scattering microscopy
2011
International audience; Transverse "chemical" interfaces are revealed with a conventional two beam narrowband coherent anti-Stokes Raman scattering microscopy setup in a collinear configuration. The exciting "pump" and "Stokes" beams are focused on the sample in two opposite directions. The subtraction of the two generated anti-Stokes signals gives rise to a signal that is directly proportional to the pure Raman spectrum of the resonant medium. This property is used to highlight an interface between glass and N,N-dimethylformamide (DMF) and recover the pure Raman spectrum of DMF around its 1408 cm−1 vibrational band.
Strong enhancement of the Breit-Wigner-Fano Raman line in carbon nanotube bundles caused by plasmon band formation
2002
We investigate the origin of the Breit-Wigner-Fano line in the Raman spectra of individual single-walled carbon nanotubes and their bundles. Using confocal Raman microscopy and atomic-force microscopy we found that the Breit-Wigner-Fano line intensity increases strongly with the bundle thickness. We confirmed this result by Raman investigations of partially decomposed bundles, which were additionally investigated by transmission electron microscopy. Our random-phase approximation based theory, which identifies the Breit-Wigner-Fano line as an excited band of plasmon-phonon modes, is fully consistent with the experimental results.
Femtosecond Raman time-resolved molecular spectroscopy
2004
Abstract The applicability of several femtosecond time resolved non-linear coherent techniques such as Raman induced polarization spectroscopy (RIPS), degenerate four-wave mixing (DFWM) and coherent anti-Stokes Raman spectroscopy (CARS) for molecular spectroscopy is presented. All methods rely on the initial coherent excitation of molecular states producing wavepackets, whose time evolution is then measured. In the case of RIPS and DFWM only pure rotational transitions are involved, whereas in CARS vibrational states can be excited. First the methodology of concentration and temperature measurements using RIPS in gas mixtures involving N2, CO2, O2, and N2O is shown. In addition some applica…
Comment on “Infrared and Raman selection rules for elastic vibrations of spherical nanoparticles”
2006
This Comment demonstrates again that selection rules established several years ago for the infrared absorption and the Raman scattering by vibrations of a spherical nanoparticle are correct and that the claimed errors about them are wrong.
Scattering and Depolarization in a Polymer Dispersed Liquid Crystal Cell
2008
An imaging polarimeter in transmission has been used to explore the effects of scatter and depolarization induced by a polymer dispersed liquid crystal cell. The experiment was carried out for three visible wavelengths. Both a directional and a scattered component can be distinguished in the light transmitted by this material. Whereas the directional component increased with voltage, the scattered portion decreased. This was a common behaviour for all three wavelengths. The polarimetric analysis revealed that the degree of polarization was also affected by changes in the voltage applied to the cell. Depolarization effects in the scattered component were usually high and decreased with volta…
Seeing a single molecule vibrate through time-resolved coherent anti-Stokes Raman scattering
2014
The vibrations of the chemical bonds of a single molecule are observed by employing time-resolved coherent anti-Stokes Raman scattering. A gold nanoantenna is used to enhance the signal from the molecule.
Temperature-Dependence of Solvent-Induced Stokes Shift and Fluorescence Tunability in Carbon Nanodots
2019
We carried out a cryogenic investigation on the optical properties of carbon dots, aiming to better understand their emission mechanism and the role of the solvent. The solvatochromic Stokes shift is quantified by a low temperature approach which allows freezing of the photo-excited state of carbon dots, preventing any solvation relaxation. Moreover, the reduction in temperature helps to identify the dynamical inhomogeneous contribution to the broadening of the emission band; therefore, disentangling the role of solvent from other types of broadening, such as the homogeneous and the static inhomogeneous contributions.
Navier-Stokes equations on an exterior circular domain: construction of the solution and the zero viscosity limit
1997
Abstract In this Note, we consider the limit of Navier-Stokes equations on a circular domain. By an explicit construction of the solution, it is proved that, when viscosity goes to zero, solution converges to the Euler solution outside the boundary layer and to the Prandtl solution inside the boundary layer.
Comparison of continuous and discontinuous Galerkin approaches for variable-viscosity Stokes flow
2015
We describe a Discontinuous Galerkin (DG) scheme for variable-viscosity Stokes flow which is a crucial aspect of many geophysical modelling applications and conduct numerical experiments with different elements comparing the DG approach to the standard Finite Element Method (FEM). We compare the divergence-conforming lowest-order Raviart-Thomas (RT0P0) and Brezzi-Douglas-Marini (BDM1P0) element in the DG scheme with the bilinear Q1P0 and biquadratic Q2P1 elements for velocity and their matching piecewise constant/linear elements for pressure in the standard continuous Galerkin (CG) scheme with respect to accuracy and memory usage in 2D benchmark setups. We find that for the chosen geodynami…
A stabilized finite element method for particulate two-phase flow equations laminar isothermal flow
1997
A finite element method for the solution of particulate two-phase flows is presented. The governing system has the form of compressible Navier-Stokes equations with unknown pressure. Therefore, the proposed method must capture the main features of stabilized methods used for incompressible as well as for compressible Navier-Stokes equations. Solution of the resulting nonlinear algebraic system of equations is based on the linearization using Newton method in conjunction with Generalized Minimal Residual iterative solver and Incomplete LU preconditioning. The method has been tested for three test cases including venturi tube flow, flow over backward step and mixing of flows in t-junction.