Effect of Plasma Shielding on Laser Ablation Rate of Pure Metals at Reduced Pressure

The ablation rate expressed as the amount of removed material per laser shot was calculated for pure metal samples under different experimental conditions: laser fluence (1.3–16.7 J cm−2), buffer gas (air, He and Ar) and gas pressure (103 –10−5 mbar). Fluence values covered the range between the plasma threshold (~1–2 J cm−2 for most elements) and 16.7 J cm−2. The 581 nm output of an excimer-pumped dye laser was used. Results pointed out a strong dependence of ablation rate on experimental parameters. At high fluence, the ablated material efficiently attenuates the incoming laser radiation (plasma shielding) and reduces the ablation rate. The extent of this shielding effect depend also on the experimental variables (buffer gas, pressure) and sample nature. These studies are useful to determine the amount of ablated material as a function of experimental parameters, to understand the extension of the shielding process and to establish the conditions under which it may be avoided. Copyright  1999 John Wiley & Sons, Ltd.