Most spectroscopic systems allow the analysis of wavenumbers down to 100 – 200 cm-1. Low-wavenumber measurements provide additional spectral information from Stokes and Anti-Stokes Raman signals close to the Rayleigh line. Therefore a specific coupler is integrated with the microscope setup which allows the acquisition of Raman spectra at wavenumbers down to below 10 cm-1. Low wavenumber measurements are often applied to the investigation of poylmorphs in pharmaceutical research, polymer research, semiconductor research, nano-carbon research and the investigation of crystallinity.
Publication regarding low-wavenumber measurements in graphene research:
C. Cong, T. Yu, Enhanced ultra-low-frequency interlayer shear modes in folded graphene layers. Nat Commun 5, 4709 (2014)10.1038/ncomms5709).