Second-order resonant Raman spectra of single-walled carbon nanotubes

An analysis of the second-order resonant Raman spectra of single-walled carbon nanotubes using different laser energies in the range 1.58--2.71 eV is presented. Major emphasis is given to the overtones and combination modes associated with the two dominant features of the first-order spectra, the radial breathing mode and the tangential mode. Both of these modes, as well as their second-order counterparts, are associated with resonant enhancement phenomena arising from electron-phonon coupling to the unique one-dimensional density of electronic states for the single-wall carbon nanotubes.