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December 2002 When one considers the impact of photonics in industry, telecommunications and aerospace immediately come to mind. Yet medical applications have witnessed an increasing advantage as well, thanks to the ability of high-power lasers to machine minute precision parts from surgical materials for implantable devices such as stents, catheters and needles. One of the most commonly applied implants is the coronary stent. This hollow tubular mesh is used following balloon angioplasty to prop open an artery that has been cleared to prevent restenosis, or recurrence of narrowing of the artery. The microstructure of the stent is a delicate scaffold composed of stainless steel or a platinum alloy that allows the artery to grow in and around the material, until it eventually becomes part of the arterial wall. The geometry of this structure is critical to how it will function once it has been implanted, and producing stents is no small feat. Igor Lukash of Gateway Laser Services has been using a high-power 532-nm Nd:YAG laser from Quantronix to produce fine curves and shapes out of stainless steel for these tubular stents. He said green lasers produce tiny features with high precision and high repeatability without heat damage. Traditional mechanical machining, which requires tools and multiple steps, is not suitable for producing small features, he explained. Another technique, called electrical discharge machining, can process only conductive materials, and chemical etching/electroforming methods are limited to the small group of metals with a simple -- mostly flat -- shape. Molding plastics and casting metals require expensive tools and are appropriate for high-volume production of parts with relatively lower precision. Lukash said that laser micromachining resolves the weaknesses of all these techniques. It can be used with almost any material: metals/alloys, ceramics, polymers, multilayered materials, semiconductors, composites and rubber. Only transparent materials, such as quartz, and some polymers, such as Teflon, are difficult to process with lasers without a sharp increase in pulse energy. Laser micromachining is a single-stage noncontact process that allows feature precision and repeatability (hole diameter, slot width, etc.) within single microns. It is suitable for prototyping, low-volume production of intricate parts and high-volume manufacturing. by Brent D. Johnson
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