Raman Spectroscopy
General Information
Inelastic light scattering from optical quasiparticles (w(q) != 0 for q = 0)
Sir C.V. Raman - Nobel prize for physics 1930
The inelastically scattered light is 12 to 14 orders of magnitude weaker than the inciden light. Typical line widths for phonon scattering in solids is several cm-1. Standard high resolution CCD Raman systems provide a spectral resolution of 0.5 cm-1 for red laser excitation.
Fundamentals of the Raman effect
Evaluation of Raman intensities needs 3rd order perturbation theory.
Electron-phonon coupling is the basic process.
Recent Developments
Resonance enhancement: The excited state is an eigenstate (RRS)
A large number of different lasers allows the study of excited electronic statesConfocal Raman system: with single monochromator and notch filter
very high light throughput, scanning Raman systems for imagingRaman microscope: high spatial resolution, 1x1 mm2
Raman near field systems: very high spatial resolution, 40x40 nm2 (NFRS)
Surface enhanced Raman scattering: strong enhancement of scattering cross section (SERS)
molecules on top of metallic nanoparticles, field enhancement and chemical enhancement High resolution Raman systems: with extended spectrometers resolution of 0.001 cm-1 can be reachedDispersive Raman modes: Raman shift depends on w1
Raman modes in quantum dots are usually dispersiveEquipment Available
Raman spectrometer
Dilor xy triple monochromator
with blue enhanced and back thinned CCD detectoin
Various gas lasers: Ar ion laser
Ar,Kr mixed gas
HeNe
NeYAG, frequency doubled
dye, tunable
Ti-saphire, tunable
About 50 laser lines in the visible spectral range can be tuned
FT Raman system
with Bruker 66v spectrometer 1064 nm NeYAG excitation