LASER-ASSISTED SURFACE MODIFICATION OF THIN CHROMIUM FILMS

The objective is to investigate a process by which micrometer scale topographical changes are produced on thin chromium films using a pulsed Nd:YLF laser. The surface of chromium films is altered through laser-induced solid-liquid phase transformation and fluid flow. Experimental parametric studies are conducted to correlate the laser parameters with the topography of the laser irradiated surfaces. Experimental and analytical work is also performed to study the transport phenomena involved in the process. A numerical finite-element analysis is used to simulate the transient field variables. A nanosecond-time-resolution, fast photography system is constructed to capture the phase change and the fluid flow occurring at the target surface. The experimental and the numerical studies showed that the surface topography change was caused by the laser-induced surface-tension-driven flow, and the recoil pressure due to surface evaporation had negligible effect on the topography variation.