Single-wall carbon nanotubes (SWNTs) were synthesized by laser ablation of Ni-Co-graphite composite targets at 1200 degreesC under argon gas. The effects of the temperature gradient near the target and the gas how rate on the diameter distribution of SWNTs were studied in order to understand their growth dynamics. Raman spectroscopy was used to analyze the diameter distribution of SWNTs. The flow rate was found to affect the relative yields of SWNTs having different diameters when the temperature gradient around the target was large. Scattering images from the ablated species at different flow rates, recorded by a high-speed video camera, indicated that 10 ms after the ablation the velocities of backward moving species increased with increasing flow rate. These findings are used to estimate the time required for determining the diameter distribution and the growth of SWNTs.