The Effect of Selective Vaporization on TEA CO_2 Laser Induced Shock Wave Plasma
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TEA CO<SUB>2</SUB> laser (130mJ, 100ns) and Nd-YAG laser (50mJ, 8ns) pulses were employed to generate secondary plasma from brass samples in air under a reduced pressure of 1 Torr. The vaporization effects on Zn and Cu were studied in terms of their emission characteristics for the two cases. In the case of TEA CO<SUB>2</SUB> laser, the emission intensities of copper spectral lines are extremely low, compared to the zinc spectral lines, indicating a highly selective-vaporization effect. The time-profiles of the emission intensities of ZnI 481.0nm and CuI 327.4nm spectral lines observed near the target surface clearly showed that vaporization of Cu atoms occurred later and continued for a long time at a relatively low gushing speed, while the vaporization of Zn atoms took place sooner with a higher gushing speed. It was shown that only Zn atoms form a shock front, and Cu atoms are left behind the shock-wave and are not excited. This selective vaporization process does not occur at a laser power density considerably higher than the threshold for the plasma generation as demonstrated by the use of Nd-YAG laser of higher power density. This phenomenon of selective vaporization described in the present paper also supports our laser-induced shock wave model.
- Bunko Kenkyu
Bunko Kenkyu 47(5), 220-227, 1998-10-15
The Spectroscopical Society of Japan