Laser micromachining of polymers

This chapter is organized in five sections. The first reviews the various lasers used in laser micromachining and the principles of interaction of laser light with matter. The second section gives examples of laser ablation of polymers and their applications. Two other sections are devoted to surface modification and generative laser processes based on layered manufacturing. Finally, a number of other laser-based processes are presented, before concluding. 

Gmeratir Micro and Nanopattems on Pofymeric Materials. Edited by A. del Campo and E. Arzt Copyri t 2011 WILEY-VCH Verlag GmbH Co. KGaA, Wemheim ISBN 978-3-527-32508-5 

Principles of Beam-Matter Interaction in Ablation Processes 

Laser radiation can be produced in different operating modes (continuous, pulsed) and in different media (solid state, gas, dye). Pulse durations range from milliseconds to femtoseconds, as in nanosecond pulsed exdmer gas lasers which radiate in the deep ultraviolet (UV) (wavelength 157 to 351 nm) and femtosecond or millisecond pulsed solid state lasers (266 to 1070 nm). Continuous wave (cw) operation CO2 gas lasers radiate in the IR (10.6 pm). 

Further important laser parameters are the pulse duration and the laser repetition rate. A short pulse duration maximizes the peak power and can reduce the thermal conduction to the surrounding material. The repetition rate can also influence the thermal impact on the material. If it is too low, the energy loss by heat conduction dominates and all of the energy not used for ablation will leave the ablation zone. Higher repetition rates lead to an increase of the average surface temperature AT which can be estimated by solving the one-dimensional heat equation for a rectangular laser pulse (Equation 8.1) [4]. 

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Waddell EA, Locascio LE, Kramer GW (2002) UV laser micromachining of polymers for microfluidic applications. JALA 7(l) 78-82... 

Zhang, Y, Lowe, R.M., Harvey, H., Hannaford, P., and Endo, A. (2002) High aspect-ratio micromachining of polymers with an ultrafast laser. Appl. Sutf. Sci., 186, 345-351. 

Ding, L., Blackwell, R.I., Kiinzler, J.F., and Knox, W.H. (2008) Femtosecond laser micromachining of waveguides in silicone-based hydrogel polymers. Appl. Optics, 47 (17/10), 3100-3108. 

Excimer Laser Micromachining [132, 133] is a technique based on laser ablation. Currently, this process can routinely ablate vias as small as 6 pm in diameter in polymers, glass, ceramics and metals. The minimum size of the features that this method can produce is limited by diffraction and by heat/mass transport. Commercial instruments and services are available from a number of companies (for example, Resonetics, Itek). 

Laser ablation is a process in which an intense btast of energy is used to remove a small amount of material fi om the surface [19]. It is the basis for excimer laser micromachining. It can be used with a variety of different materials, ranging from silicon to polymers and ceramics. Feature sizes in the low micrometer range can be realized. The advantage of laser ablation is the... 

Research in laser micromachining wiU continue to new methods for the fabrication of microfluidic devices, particularly from polymers and glass. The development of 3D channel networks is important for numerous fluidic applications which wiU fuel the future demand for more research in this area. As these methods are refined, the processes wiU be tailored to processing of many different types of polymers. Future work will continue to seek methods to decrease the roughness of microchannels. 

Research in laser micromachining will continue to new methods for the fabrication of microfluidic devices, particularly from polymers and glass. The development of... 

Laser micromachining is also used to fabricate biodegradable microdevices for biomedical applications [53]. Ghen et al. [54] reviewed the advancements of laser micromachining for etching biodegradable polymers and concluded that deep UV lasers operating at 193 nm were a better choice to minimize the photothermal effect. 

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