UV-visible spectroscopic study of CO2 laser produced tin plasma

A novel technique that is able to achieve high spatial resolution in the measurement of the spectral emission characteristics of laser produced expanding plasmas is reported. The image of expanding laser produced plasma is directly focused on the entrance slit of a stigmatic spectrometer coupled with image readout intensified charge-coupled device camera. The parallel spectra acquisition approach of this measurement has a better spatial resolution than conventional plasma emission spectroscopy measurements at different distances from the target. Based on the high spatial resolved measurements, the plasma plume UV-visible emission spectra in a vacuum of 10(-4) Pa by pulsed CO2 laser ablating tin were obtained. Analysis of the spectra provides useful plasma parameters. Relative ion emission intensities provided electron temperature, and Stark broadened line widths yield electron densities. The high spatial resolution emission images give the plasma plume expansion dynamics. The understanding of the temporal and spatial distribution of laser produced plasma parameters of tin is of great interest to the control of the extreme ultraviolet emission process for lithography.