In situ optical emission spectroscopy (OES) was used to investigate the spatial and temporal evolution of C-2, the electron density (N-e) and the electron temperature (T-e) of laser induced plasmas in the laser-furnace method of synthesizing single-walled carbon nanotubes (SWCNTs). The intensities of the spectral maps of C-2; N-e and T-e showed a strong temperature dependence. The frequency of sharp fluctuations which appear as hot spots in the spectral maps of N-e and T-e increased as the furnace temperature was increased from 1073 to 1273 K. We suggest that the appearance of hot spots is a result of the heat of formation of SWCNTs. (C) 2010 Elsevier B. V. All rights reserved.