Owing to the highly transitory behaviour of laser-produced plasma

it is difficult to found the mechanism of plasma radiating because of the process of ablation being complicated.It is the most important to characterize the laser produced plasma (LPP)in a time- and space-resolved way. In the paper

optical emission spectroscopy is used to characterize the plasma produced by 308 nm

20 ns XeCl excimer laser ablation of Cu target in low pressure. Time- and spatial-resolved measurements of optical emission produced by XeCl excimer laser ablation of Cu in low pressure were reported. The pressure of ablation chamber was 1 Pa air. The temporal variation of the spectrum lines intensities was analyzed.The plasma plume photograph from XeCl excimer laser ablation of Cu was taken by camera in air with pressure of 1 Pa. The experimental results show that the plume has different colour in different region

the core region of the plume is white

the middle region of the plume is yellow and purple

etc

the outskirts region of the plume is green.The experimental results may be explained using a theory model based on that plume is made of three region and the region detail species excitation mechanism is different from each another. The continuum background emission comes from the Bremsstrublung emission of electrons ejected from target. The excited copper atoms and ions may be produced from different mechanism

the atoms excitation mechanism in plume is electron collision energy transfer and recombination of electron and ion

but the ions excitation mechanism in plume is electron collision energy transfer only. The results show that the most possible plume radiation mechanism is dual excitation model

it can be used to explain the experimental results that the simple excitation model can to do

and can be used to explain the experimental results that the simple excitation model can not to do. We found that the plume radiation mechanism obtained in low pressure is accuracy and direct to that of at the pressure of one atmosphere.