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Femtosecond Lasers: A Solution Looking for a Problem

Originally Published MPMN June 2001

EDITOR'S PAGE

Femtosecond Lasers: A Solution Looking for a Problem

High-power ultrashort-pulse laser systems have been migrating from research laboratories to industrial environments for the past couple of years. Although commercial applications have been limited to niche areas, the technology has much broader potential according to researchers. Adding his voice to the chorus, John Girkin, a physicist at the Institute of Photonics, University of Strathclyde, in Glasgow, Scotland, explained the machining capabilities of femtosecond lasers at a conference on medical polymers in Brussels. Describing the technology as a "solution looking for a problem," he invited attendees at the meeting, organized in May by Rapra Technology Ltd., to seek industrial applications for the tool. It occurred to me that MPMN readers might be interested in taking part in the challenge, as well.

Femtosecond lasers deliver pulse durations that can be as short as a few femtoseconds (10-15 second). Girkin put this in perspective by pointing out that light travels fast enough to circle the world seven times per second and crosses a human hair in 100 femtoseconds. These pulses are too short to transfer heat or shock to the material being processed. Consequently, there is little to no "collateral damage" to the surrounding material, said Girkin. This represents a clear advantage over thermal cutting and plasma ablation, the dominant laser-based machining techniques currently used by industry.

Ultrashort-pulse lasers break the material's intermolecular bonds in a manner similar to excimer lasers, noted Girkin, but they do so in near-infrared wavelengths. The UV light generated by excimer lasers can cause plasma to form in front of the workpiece, and these clouds absorb subsequent light pulses and distort the incoming beam. Femtosecond lasers deposit their energy so quickly that the beam does not interact with the plume of vaporized material. In principle, this enables "ultrashort laser systems to run at much higher repetition frequencies" than UV systems, according to Girkin.

Device designers and manufacturers should also be impressed by the precision of these systems, said Girkin. Holes measuring less than 100 µm have been ablated, and the lasers are able to machine inside materials without causing surface damage. Single pulses can be adjusted to remove material measuring only a few nanometers in thickness. To illustrate the laser's precision and the minimal energy or mechanical shock that is transferred to the material, Girkin cited an experiment conducted at Lawrence Livermore Laboratories in California, where researchers have used the system to machine an unstable and highly explosive material without causing it to detonate.

Thus far, the femtosecond laser has been used to machine materials ranging from collagen to metal with equally remarkable results. In all instances, the workpieces exhibited a similar cutting profile, and little or no damage was observed on the surrounding surface.

When evaluating femtosecond lasers for an industrial application, "there are some considerations to keep in mind," acknowledged Girkin. "They are not fast [in terms of throughput], they are not suited for drilling holes in the millimeter range, and the systems are currently priced at about $200,000." On the other hand, if you are looking for a tool to perform high-precision cutting with little or no collateral damage, then a femtosecond laser may indeed be worth a look. As for the price tag? Everything's relative, noted Girkin: if the femtosecond laser provides you with an enabling technology for an application that otherwise might not be feasible, then you might call it a bargain.

To find out more about research on femtosecond lasers conducted by Girkin and his colleagues, you can contact him via e-mail at [email protected].

Norbert Sparrow

Copyright ©2001 Medical Product Manufacturing News

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