Transport Phenomena and Droplet Formation During Pulsed Laser Interaction With Thin Films

Abstract

This work investigates transport phenomena and mechanisms of droplet formation during a pulsed laser interaction with thin films. The surface of the target material is altered through material flow in the molten phase induced by a tightly focused laser energy flux. Such a process is useful for developing a laser-based micromachining technique. Experimental and numerical investigations of the laser-induced fluid flow and topography variations are carried out for a better understanding of the physical phenomena involved in the process. As with many machining techniques, debris is often generated during laser-material interaction. Experimental parametric studies are carried out to correlate the laser parameters with the topography and droplet formations. It is found that a narrow range of operation parameters and target conditions exists for “clean” structures to be fabricated. The stop action photography technique is employed to capture the surface topography variation and the melting development with a nanosecond time resolution and a micrometer spatial resolution. Numerical simulations of the laser-induced surface deformation are also performed to obtain the transient field variables and to track the deforming surface. The comparison between the numerical and experimental work shows that, within the energy intensity range investigated in this work, the surface deformation and droplet formation are attributed to the surface-tension-driven flow, and the recoil pressure effect plays an insignificant role in the surface topography development. [S0022-1481(00)02903-0]

The Effect of Crystal-Melt Surface Energy on the Stability of Ultra-Thin Melt Films

“…At the CM interface, the unit normal vector pointing from solid into liquid iŝ 12) and the tangential vector isτ…”

“…A thin disk region of material is liquefied, producing a film bounded on one side by its crystal and on the other by a melt-gas interface. One significant difference is that a longitudinal temperature gradient develops due to the Gaussian energy intensity distribution of the laser flux [12]. Hence, Marangoni effects will heavily influence the interface morphology.…”

Nanodrilling of fused silica using nanosecond laser radiation

“…The high laser fluence irradiation of metal on dielectric surfaces using ns laser radiation results in an ablation process of the metal and in a modification of the dielectric surfaces like localized ablation and melting effects [31][32][33]. The ns laser metal nanostructuring process exhibit different physical effects: photon-solid interaction [29], phase transition, and solid-liquid interaction [24,[34][35][36][37][38][39].…”

A numerical analysis of heat and fluid flow with a deformable curved free surface in a laser melting process

“…The transient surface deformations of Ni-P disk substrates and metallic thin films upon pulsed laser heating have been investigated experimentally (Baumgart et al, 1995;Chen et al, 2000;Willis and Xu, 2000). They found several kinds of the surface shapes (V-type bump, sombrero bump, and double-rim bump) resulting from different pulse energies of the heating laser beam.…”