This paper describes a direct write laser technology, which is fast and flexible, for fabricating multiple-level microfluidic channels. A high brightness diode-pumped Nd-YAG laser with slab geometry was used for its excellent beam quality. Channels with flat walls and staggered herringbone ridges on the floor have been successfully 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 the radius of a parent vessel equals the sum of the cubes of the radii of the daughters. The multi-depth architecture allows for flow patterns to resemble physiological vascular systems with lower overall resistance and more uniform flow velocities throughout the network compared to planar patterning techniques which generate uniformly thin channels. 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.

We show that silver lines patterned on a substrate with multiphoton absorption can be rendered electrically conductive using electroless enhancement with copper. We demonstrate that this technique can be used to create metallic features on three-dimensional polymeric structures that have been fabricated with multiphoton absorption polymerization. This method makes it possible to use multiphoton absorption to create complete metal/polymer hybrid microstructures with a single fabrication setup.

Equivalent ion temperature in Ta plasma produced by high energy laser ablation J. Appl. Phys. 99, 083301 (2006); 10.1063/1.2189932Electronic temperature and density of the plasma produced by nanosecond ultraviolet laser ablation of LiF

A fundamental study on the Q-switched diode-pumped solid-state laser interaction with silicon was performed both experimentally and numerically. Single pulse drilling experiments were conducted on N-type silicon wafers by varying the laser intensity from 10 8-10 9 W cm −2 to investigate how the mass removal mechanism changes depending on the laser intensity. Hole width and depth were measured and surface morphology was studied using scanning electron microscopy. For the numerical model study, Ki et al's self-consistent continuous-wave laser drilling model (2001 J. Phys. D: Appl. Phys. 34 364-72) was modified to treat the solidification phenomenon between successive laser pulses. The model has the capabilities of simulating major interaction physics, such as melt flow, heat transfer, evaporation, homogeneous boiling, multiple reflections and surface evolution. This study presents some interesting results on how the mass removal mode changes as the laser intensity increases.

Silicon has been widely used to fabricate microfluidic devices due to the dominance of silicon microfabrication technologies available. In this paper, theoretical analyses are carried out to suggest suitable laser machining parameters to achieve required channel geometries. Based on the analyses, a low-power CO 2 laser was employed to create microchannels in Acrylic substrate for the use of manufacturing an optical bubble switch. The developed equations are found useful for selecting appropriate machining parameters. The ability to use a low-cost CO 2 laser to fabricate microchannels provides an alternative and cost-effective method for prototyping fluid flow channels, chambers and cavities in microfluidic lab chips.

Multiphoton absorption has become a powerful technique for the creation of three-dimensional micro- and nanostructures. Here we review some of our recent progress towards creating functional microdevices with multiphoton absorption. Specific thrusts of our research include development of new resins for multiphoton absorption polymerization, design of novel schemes for metal deposition, and post-fabrication ablation of polymeric structures.

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