Time resolved emission spectroscopic measurements on a plasma plume generated by pulsed laser ablation of carbon in helium ambient atmosphere have been performed. Temporal profiles of electronically excited C-2 species show a twin peak distribution beyond a threshold laser irradiance. The emission features of C-2 species are found to be significantly influenced by the ambient helium atmosphere. It is observed that the helium ambient pressure and laser irradiance have opposite effects on the expansion dynamics of C-2 species.