We outline results obtained from Schlieren and dye laser resonance absorption imaging of the plume ejected from an aluminum target in a nitrogen atmosphere of 1 bar and 100 mbar by a KrF excimer laser (lambda equals 248 nm, FWHM equals 30 ns). The results show that for relatively low and high laser fluences (14 J/cm² and 36 J/cm²), the plume closely follows the shock wave which is generated by the ablated material pushing against the surrounding gas. Calculations of the evolution of the ambient gas and ablated material show that the temperature and electron density vary greatly depending on the laser fluence and the external gas pressure. We report maximum plasma temperatures of 39888 K and electron densities of 4.2 multiplied by 10²⁶ m^-3 for a laser fluence of 36 J/cm². These results indicate that inverse bremsstrahlung may play a very significant role in how the laser pulse energy is distributed in the plume for high laser fluences.

Date Published: 9 May 1997
PDF: 8 pages
Proc. SPIE 2991, Laser Applications in Microelectronic and Optoelectronic Manufacturing II, (9 May 1997); doi: 10.1117/12.273733

Published in SPIE Proceedings Vol. 2991:
Laser Applications in Microelectronic and Optoelectronic Manufacturing II
Jan J. Dubowski, Editor(s)