Broadening and attenuation of UV laser ablation plumes in background gases

The expansion of a laser-induced silver plume in a background gas has been studied in a variety of gases ranging from helium, oxygen and argon to xenon. We have measured the angular distribution of the total deposit of silver on an array of quartz crystal microbalances as well as the time-of-flight distribution with a Langmuir probe. The angular distribution broadens for all gases except for a minor pressure range for the helium background gas, in which a distinct plume narrowing occurs. The behavior of the collected, ablated silver atoms integrated over the full hemisphere is similar for all gases. This integral decreases strongly above a characteristic pressure, which depends on the specific gas. The ion time-of-flight signal shows a clear plume splitting into a fast and a slow component except for the ablation plume in a helium gas. (c) 2005 Elsevier B.V. All rights reserved.