title: A low-wavenumber-extended confocal Raman microscope with very high laser excitation line discrimination.
abstract: We describe the simple modification of a confocal Raman imaging microscope to incorporate two ultra-narrow holographic notch filters. The modified microscope rejects the laser excitation line (Rayleigh peak) by a discrimination factor of ∼10(11) and allows simultaneous measurements of Stokes/anti-Stokes Raman shifts as close as ∼10/20 cm(-1) to the Rayleigh line. The extremely high rejection ratio of the Rayleigh peak results in its intensity becoming comparable to typical Raman scattering signals. This is essential for micro-Raman spectroscopy and imaging in the low-wavenumber region. We illustrate the resulting performance with measurements on silicon/silica, sapphire, sulfur, L-cystine, as well as on single-walled carbon nanotubes (SWNTs). We find that both aggregated (bulk) and individual (deposited on substrate) SWNTs demonstrate strong and broad characteristic Raman features below ∼100 cm(-1)-in a region which has remained essentially unexplored in measurements of bulk SWNT samples and which has so far been inaccessible for Raman spectroscopy of individual SWNTs.
authors.affiliation: Karlsruhe Institute of Technology, Institute of Nanotechnology, Germany. sergei.lebedkin@kit.edu.
authors.forename: Sergei
authors.initials: S
authors.lastname: Lebedkin
authors.forename: Carolin
authors.initials: C
authors.lastname: Blum
authors.forename: Ninette
authors.initials: N
authors.lastname: Stürzl
authors.forename: Frank
authors.initials: F
authors.lastname: Hennrich
authors.forename: Manfred M
authors.initials: MM
authors.lastname: Kappes