Frequency shifts in stimulated Raman scattering

The nonresonant contributions to the nonlinear susceptibility χ(3) produce a frequency chirp during stimulated Raman scattering. In the case of transient stimulated Raman scattering, the spectrum of the generated Stokes pulse is found at higher frequencies than expected from spontaneous Raman data. The frequency difference can be calculated from the theory of stimulated Raman scattering

A micro-magneto-Raman scattering study of graphene on a bulk graphite substrate

We report on a magneto-Raman scattering study of graphene flakes located on the surface of a bulk graphite substrate. By spatially mapping the Raman scattering response of the surface of bulk graphite with an applied magnetic field, we pinpoint specific locations which show the electronic excitation spectrum of graphene. We present the characteristic Raman scattering signatures of these specific locations. We show that such flakes can be superimposed with another flake and still exhibit a graphene-like excitation spectrum. Two different excitation laser energies (514.5 and 720 nm) are used to investigate the excitation wavelength dependence of the electronic Raman scattering signal.Comment: 6 pages, 5 figure

Theory of Raman Scattering from Orbital Excitations in Manganese Oxides

We present a theory of the Raman scattering from the orbital wave excitations in manganese oxides. Two excitation processes of the Raman scattering are proposed. The Raman scattering cross section is formulated by using the pseudospin operator for orbital degree of freedom in a Mn ion. The Raman spectra from the orbital wave excitations are calculated and their implications in the recent experimental results reported in LaMnO$_3$ are discussed.Comment: 10 pages, 7 figure

Raman scattering in current carrying molecular junctions. A preliminary account

This is a preliminary acount of a theory for Raman scattering by current-carrying molecular junctions. The approach combines a non-equilibrium Green's function (NEGF) description of the non-equilibrium junction with a generalized scattering theory formulation for evaluating the light scattering signal. This generalizes our previous study (Phys. Rev. Lett. 95, 206802 (2005); J. Chem. Phys. 124, 234709 (2006)) of junction spectroscopy by including molecular vibrations and developing machinery for calculation of state-to-state (Raman scattering) fluxes within the NEGF formalism. For large enough voltage bias we find that the light scattering signal contains, in addition to the normal signal associated with the molecular ground electronic state, also a contribution from the inverse process originated from the excited molecular state as well as an interference component. The effect of coupling to the electrodes and of the imposed bias on the total Raman scattering as well as its components are discussed. Our result reduces to the standard expression for Raman scattering in the isolated molecule case, i.e. in the absence of coupling to the electrodes. The theory is used to discuss the charge transfer contribution to surface enhanced Raman scattering for molecules adsorbed on metal surfaces and its manifestation in the biased junction.Comment: 46 pages, 7 figure

Sum-frequency ionic Raman scattering

In a recent report sum-frequency excitation of a Raman-active phonon was experimentally demonstrated for the first time. This mechanism is the sibling of impulsive stimulated Raman scattering, in which difference-frequency components of a light field excite a Raman-active mode. Here we propose that ionic Raman scattering analogously has a sum-frequency counterpart. We compare the four Raman mechanisms, photonic and ionic difference- and sum-frequency excitation, for three different example materials using a generalized oscillator model for which we calculate the parameters with density functional theory. Sum-frequency ionic Raman scattering completes the toolkit for controlling materials properties by means of selective excitation of lattice vibrations

Two-magnon Raman scattering in spin-ladder geometries and the ratio of rung and leg exchange constants

We discuss ways in which the ratio of exchange constants along the rungs and legs of a spin-ladder material influences the two-magnon Raman scattering spectra and hence can be determined from it. We show that within the Fleury-Loudon-Elliott approach, the Raman line-shape does not change with polarization geometries. This lineshape is well known to be difficult to calculate accurately from theory. However, the Raman scattering intensities do vary with polarization geometries, which are easy to calculate. With some assumptions about the Raman scattering Hamiltonian, the latter can be used to estimate the ratio of exchange constants. We apply these results to Sugai's recent measurements of Raman scattering from spin-ladder materials such as La$_6$Ca$_8$Cu$_{24}$O$_{41}$ and Sr$_{14}$Cu$_{24}$O$_{41}$.Comment: 5 pages, revtex. Latest version focuses on ladder materials, with a detailed examination of the role of Heisenberg-like coupling constants which appear in the Fleury-Loudon-Elliott scattering operator but are rarely discussed in the literatur

The next generation of advanced spectroscopy : surface enhanced raman scattering from metal nanoparticles

Surface enhanced Raman scattering (SERS) has enjoyed an ever growing research base since its discovery with the number of papers published using the technique and investigating the basis behind it growing exponentially year by year.[1] SERS is an advancement of Raman scattering which overcomes some of the limitations of normal Raman scattering. Raman scattering is a vibrational spectroscopy which gives molecularly specific information relating to specific molecular species. The disadvantage of Raman scattering is that it is an inherently weak process, however it can be used in aqueous solutions, due to water being a weak Raman scatterer, lending itself to analysis and study of molecules in aqueous solution including the study of biomolecules. Another major disadvantage is the fluorescence which often accompanies Raman scattering and can sometimes overwhelm the bands in the spectrum rendering the experiment useless. To overcome this, the phenomenon of surface enhanced Raman scattering can be used