Laser-induced effects in Raman spectra of single-wall carbon nanotubes

Two effects induced by increasing power density of a probe laser beam are discovered in Raman spectra of single-wall nanotubes: the irreversible disappearance of the 'breathing' Raman modes of small-diameter nanotubes (0.8 — 1 nm) and the reversible appearance of additional 'breathing' modes from nanotubes with diameters 0.1 — 0.3 nm smaller than the diameters of nanotubes undergoing resonance Raman excitation at room temperature. The thermal nature of these effects is confirmed by their reproducibility upon heating of the material in an optical oven.