Comparison research on the laser plasma spectra with and without obvious self-absorption

Characteristics of laser produced Pb plasma were investigated using the spectrograph and the fast photography by an intensified charge coupled device (ICCD) camera. The optical emission spectra and images of the plasma were recorded and analyzed. The clear self-reversed structure can be revealed in the emission spectra of the lead plasma when the target is at 6 mm before the focus of lens. However, the self- absorption can not be observed in the spectra if the target is located at the focus. The electron temperature, the electron number density and the lower level atomic number density were obtained by fitting the experimental spectra at different delay times under the two circumstances. The electron number density and the lower level atomic number density are higher, as the target is at 6 mm before the focus of lens, however the electron temperature is lower as the target is located at the focus, under the same laser energy