Laser induced plasma is a relatively complex process which is closely related to many factors. In this paper, using a short pulse Nd:YAG laser and CCD photoelectric detection system, the variation of laser focus position effected by spectral intensity, the ratio of signal to background as well as the self-absorption of the plasma spectral lines with the standard spectra sample of aluminum for analysis samples was studied. Results show that: when the laser focus position is about 5mm under the surface of the sample, the relative intensity and the ratio of signal to background of the spectral lines are the strongest, and the spectral lines are sharp without obvious self-absorption.
