Laser processing of aluminum alloy 5754 and silicon using a high brightness diode-pumped solid-state niodymium:YAG laser (DPSSL).

Abstract

This research investigates the application of a new generation high average power, high brightness DPSSL to understand the high power aspect of the laser for laser welding of aluminum alloy and the studies of plasma formation during the process via laser emission spectroscopy and the low power aspect of the laser for laser micromachining of silicon to create microchannels for microfluidic applications. First, this research describes bead-on-plate keyhole welding on Aluminum Alloy 5754 using the laser's maximum average power available. In addition to penetration depth data, spectral lines from Aluminum I transitions are examined. Emission spectroscopy revealed the temperature of the vapor plume to be typically 8000--10000 K at the surface of the workpiece. A lower plume temperature is observed, which correlates to parameters leading to deeper penetration. Second, this research describes a direct write laser technology for fabricating multiple-level microfluidic channels. Channels with nearly straight flat walls and staggered herringbone ridges on the floor have been fabricated and their ability to perform passive mixing of liquid is discussed. Also, a multi-width multi-depth microchannel has been fabricated to generate biomimetic vasculatures whose channel diameters change according to Murray's law, which states that the cube of radius of a parent vessel equals the sum of the cubes of radii of the daughters. The ability to directly fabricate multiple-level structures using relatively straightforward laser technology enhances our ability to rapidly prototype complex lab-on-a-chip systems and to develop physiological microfluidic structures for tissue engineering and investigations in biomedical fluidics problems. Last, in order to develop fundamental understanding of micromachining with DPSSL, a case study based on a previously developed two-dimensional axisymmetric self-consistent continuous-wave laser drilling model together with the implementation of fluid melt flow, evaporation, kinetic Knudsen layer, multiple reflections and homogeneous boiling processes near the critical point has been employed for pulsed laser beam and preliminary results are discussed.