Carbon nanotubes (CNTs) were produced by laser ablation of a graphite composite target in argon and nitrogen ambient gas. To investigate the effect of nitrogen gas on CNTs formation, the plasma plume was examined using optical emission spectroscopy. The vibrational temperature of C, molecules was estimated by fitting of a Swan band spectrum. The temperature in N, ambient gas is lower than that in Ar ambient gas. In a nitrogen atmosphere, the spectrum intensity of C, Swan band was enhanced and CN violet system was also observed. Soot collected in the reaction tube was observed using FE-SEM and TEM. The soot deposited in the nitrogen gas contained more bundled CNTs than those in Ar ambience. (C) 2003 Elsevier B.V. All rights reserved.