Taking the Pulse of Medical Device Laser Processing

Apropos of the 50th anniversary of the laser this year, laser technology seemed to be ubiquitous at last week's BIOMEDevice trade show in San Jose. And it seems as though after 50 years, lasers for medical device manufacturing are primed for change.

Two back-to-back presentations at the show's Innovation Briefs Theater focused on various aspects of laser processing for medical device manufacturing. First up, Tony Hoult of IPG Photonics (Oxford, MA) stated his case for why flashlamp-pumped solid-state lasers should be replaced with fiber lasers in the medical device industry.

The same basic laser concept that was invented 50 years ago is still widely used today. However, Hoult essentially maintains that everything flashlamp-pumped lasers can do, fiber lasers can do better. "This fiber laser concept has been moved forward to produce a new, high-pulse-energy fiber laser, which can do everything that a flashlamp-pumped laser can do."

Capable of emitting pulses ranging from 0.2 to 20 ms--which is comparable to those of a flashlamp-pumped laser--fiber lasers can perform cutting, welding, and drilling operations. They also have a 10-micron core, nondiscrete optical components, no thermal gradients, an air-cooled design, and a large surface-to-volume ratio. Furthermore, a choice of delivery fibers allows for a range of spot sizes and features to be produced while temporal shaping of the pulse with time can facilitate pacemaker welding, Hoult adds. "It's a very simple, scalable, elegant concept with the end result being scalability, reliability, and, ultimately, performance."

In addition to pacemaker welding, fiber lasers are suited for angioplasty stent cutting, processing difficult-to-weld metal alloys, and microwelding applications. "There's a new breed of diode-pumped, high-pulse-energy fiber lasers available," Hoult states. "There's a radical shift in the industry. They can do everything flashlamp-pumped lasers can do, but using 10 times less power and floor space."

Stefan Quandt of Rofin-Sinar (Hamburg, Germany) followed Hoult, beginning his presentation by declaring that he, for the most part, agreed with Hoult's assessment that fiber lasers hold a great deal of promise for medical device manufacturing. However, he noted that there is a place for other technologies as well.

Quandt focused his presentation on assessing laser cutting versus laser ablation. Laser ablation, he says, can allow manufacturers to process a part without yielding dross or debris and can avoid heat absorption in the material.

"Most polymers do not absorb laser energy well in the wavelengths ranging from 355 nm to 12 nm," he says. "You can use a fiber laser and apply that energy to most polymers without the polymer reacting to this material, meaning that when you do polymer fusion or welding, you may have to add absorbent materials to it. This shows us if you want to laser-cut polymer, a traditional YAG laser or fiber laser will not work easily. You have to use tricks like absorbers in the polymer to cut those materials. However, when you go to very short pulse lengths, this changes and it is possible with 1500-nm wavelength laser to [process] most polymers without the need of traditional absorbers."

Femtosecond lasers, in particular, help to avoid by-products such as burrs and heat-affected zones, Quandt advises. Not only is it important to bypass these by-products because they can result in the need for costly secondary cleaning operations, but heat-affected zones can cause microcracking as well, according to Quandt. Thus, the integrity of the part can be compromised. -- Shana Leonard