Abnormal Anti-stokes Raman Spectra of Single Walled Carbon Nanotubes Raised from Coherent Anti-stokes Raman Scattering and Optical Cooling Processes

For the single-walled carbon nanotubes, the higher values of anti-Stokes/Stokes Raman intensity ratio (Ias/Is) then the predictions of the Maxwell-Bolzmann formula indicates a CARS emission resulting from a wave mixing process between the incident laser light (ωl) and Stokes Raman light (ωs) generated by a SERS mechanism . The weaker value of (Ias/Is) observed at resonant excitation of semiconducting nanotubes in the E22 van Hove state , relates a quantum cooling process occurred during the relaxation of the E22 excited state in two steps by phonon emission from E22 to E11 followed by a spontaneous luminescence emission at E11.