New Laser Technologies Displacing Old

HANK HOGAN, CONTRIBUTING EDITOR, hank.hogan@photonics.com

For some CO₂ laser applications, the end is at hand, with fiber lasers having almost totally replaced the older technology. Another shift currently brewing is due to the arrival of high-power diode lasers, which are impacting materials processing and driving down the cost of ultrafast lasers through the advent of direct diode pumping.

Replacing CO₂ lasers with fiber lasers increases metal cutting speeds 2 to 5×. Courtesy of Bystronic.

In these transitions, the lasers that win out typically cost less, are easier to operate and are more robust. They also may offer other advantages: a wavelength that materials absorb more readily or that lends itself to greater precision.

But these newcomers shouldn’t get too comfortable. Exotic technologies — like powerful blue lasers today and organic lasers years down the road — are likely to make their mark. In part, this will be by displacing, to some degree, today’s winners.

A close-up of a blue laser in action on copper material. Courtesy of Nuburu.

The recent replacement of CO₂ lasers by fiber systems is illustrated by the shift in the mix at Bystronic Laser AG for its sheet metal cutting systems.

“Two years ago, we were probably already at 70 percent fiber. Now, we’re probably almost 100 percent fiber for the North American market,” said Frank Arteaga, the company’s head of product marketing for the NAFTA region.

That is telling because Bystronic, a Niederönz, Switzerland-based manufacturer of materials processing systems, started out in 1986 with a CO₂ laser sheet metal cutting machine. The company stayed with the technology until sufficiently powerful, single-mode fiber lasers were available. Bystronic offered its first fiber laser sheet metal cutting system in 2009.

The wavelength-dependent energy absorption by metals at 295K. Courtesy of Nuburu.

The new laser technology offered advantages, Arteaga said. The systems were more robust and required less maintenance than those based on the older technology. Together, that cut the operational cost per hour in half. As for throughput, that ranged anywhere from two to five times faster with the switchover to fiber lasers.

Same power, higher throughput

In part, the speedup was due to the shift in wavelength. A CO₂ laser operates at 10 µm, whereas the fiber lasers used by Bystronic emit at 1.06 µm. The shorter wavelength was much more readily absorbed by the metals being cut, which meant that for the same power, throughput went up. The shorter wavelength also could be focused down to a smaller spot, increasing power density.

The switch at Bystronic is one the entire industry has undergone. According to a March 2016 report from market research firm Optech Consulting, fiber lasers now account for more of the global materials processing than do CO₂ and excimer lasers.

In this changeover, an important point to remember is that the dominance of fiber is in new units. The industry has been selling CO₂ systems for at least 25 years, so there is a substantial installed base that needs to be replaced, according to Arteaga. He estimates that there are 10,000 such units.

Part of the reason fiber has overtaken CO₂ in cutting and other applications is the steady rise in the power of the solid-state lasers. Bryce Samson, director of North American sales for IPG Photonics Corp., an Oxford, Mass.-based maker of fiber lasers and amplifiers, said that five or six years ago, the average power of fiber laser in a cutting system stood around 2 kW.

“Now the average is somewhere between 6 and 8 kW, with the new products introduced at 12 to 14 kW. Most of that is finding its way into cutting thicker materials because OEMs are finding out how to match the traditional cut quality they got from CO₂. So, even that last foothold for CO₂ is going to be eroded in the next five years,” he said.

A schematic of the laser. Optimizing the device structure and using appropriate materials extended the duration of lasing up to 30 ms, more than 100 times longer than previously possible. Courtesy of Atula S.D. Sandanayaka and Willam J. Potscavage Jr., Kyushu University.

Samson added that the key requirement for any industrial application is that the laser source be small, compact, reliable and cost-effective. The reliability must be such that systems can run potentially three shifts a day for years, with the only downtime being routine maintenance.

It’s also important that wavelengths well suited for the task be available, and for fiber lasers that means the right dopants must be found, investigated and then commercialized. IPG is currently working to develop sources in the 2- to 10-µm range, using its own resources and those of universities and elsewhere for this. Through frequency doubling or tripling, the company is also getting into green and ultraviolet wavelengths.

In addition to more power and new wavelengths, fiber lasers are also entering the arena of ultrafast processing, with pulse widths that are a nanosecond or less. Thanks to their inherent reliability, fiber systems are well placed to take market share in that area, Samson said.

Ultrashort-pulse-width lasers enable precision machining, which makes them candidates for fine materials processing. Examples include electronics and tight tolerance mechanical systems, such as fuel injection nozzles.

Today, a dominant technology for this is Ti:sapphire lasers. Here, too, a laser replacement may be on the verge of altering the landscape. Thanks to recently introduced single-emitter, high-power blue diode lasers, KM Labs Inc. of Boulder, Colo., has started shipping direct diode-pumped ultrafast lasers. This can drop the cost of the Ti:sapphire system by as much as $50,000, according to CEO Henry Kapteyn. This could make it possible for Ti:sapphire ultrafast laser technology to enter new applications.

Typical operation with a high-power fiber laser. Courtesy of IPG Photonics.

Kapteyn noted that at times the switch from one laser technology to another is driven by outside factors. For instance, handheld electronics, such as smartphones, demand ultrahigh-precision manufacturing. That, in turn, means the traditional approach of a printed circuit board with holes drilled by older laser technology cannot achieve a high enough density of components.

“PC boards are being superseded by SoC, or system-on-chip, architectures that are much denser,” Kapteyn said. “This, again, presents an opportunity for a higher precision laser technology, and will drive adoption of new technologies.”

He added that, overall, industrial materials processing will continue to move increasingly away from brute force mechanical methods. Laser-based systems should, therefore, see continuing growth.

High absorption rates

The advent of high-power blue laser diodes could yield a second example of one technology replacing another, according to Jean-Michel Pelaprat, chief marketing and sales officer of Nuburu Inc. of Centennial, Colo. Nuburu products are designed to take on IR lasers, such as fiber, and other materials processing systems in various applications.

One such application is the welding of copper foils used in the cathodes of lithium-ion batteries in cars. The absorption of copper in the IR is only 5 percent.

New high-power blue diode laser technology enables welding and other material processing of copper, something IR lasers have trouble with. Close-ups of copper welds: conduction mode (a) and keyhole weld (b). Courtesy of Nuburu.

“In the blue, the absorption is 65 percent,” Pelaprat said.

Currently, the low absorption rate means that IR lasers cannot be used for this welding task, which demands a joint that is high quality with good electrical connection and mechanical strength. Today, this welding is done ultrasonically, but Nuburu aims to change that and address other copper welding applications currently performed by IR lasers. Welds done at the longer wavelength tend to result in splatter, according to Pelaprat. That can cause shorts, so any splatter must be removed in processing after welding.

The greater absorption at blue wavelengths as compared to IR is true for other metals, ranging from a half again increase for stainless steel to as much as 1000-fold gain for gold. This means that a low-power blue diode laser may offer throughput of a much higher-power IR system, depending on the application.

Stainless steel cut up to 30 mm thick using a 6-kW fiber laser. Courtesy of IPG Photonics.

For instance, copper foils are thin and can be welded by the 150-W blue diode laser system available later this year from Nuburu. For thicker material, more power will be needed, which should come about as systems of higher power become available, Pelaprat said.

With regard to what new laser technology may make an impact years from now, one possibility is organic thin-film lasers. Such lasers could more easily enable certain colors and could potentially be mass-produced at a low cost. They could be mounted in flexible systems or provide the light source for medical diagnostics.

Blue organic thin-film laser under operation. Courtesy of Atula S.D. Sandanayaka and Willam J. Potscavage Jr., Kyushu University.

“They might be useful as light sources for disposable lab-on-a-chip devices used for a variety of measurements or tests,” said Chihaya Adachi, director of the Center for Organic Photonics and Electronics Research at Japan’s Kyushu University.

Adachi has investigated organic electronics and photonics for decades. He was a co-author of a recent Science Advances paper: “Toward continuous-wave operation of organic semiconductor lasers.” Among the issues being investigated by researchers are how to extend emitter lifetimes and how to create an electrically pumped organic laser.

Adachi said it will be years before the first and most basic applications of the new technology appear. Initially, the power levels of the lasers are likely to be low. Thus, the technology to be replaced first by the new lasers might be low-power laser diodes.

While this may happen in the future, today fundamental material research is ongoing, in part because the payoff of success could be significant. According to Adachi, “We will continue the challenge because we would like to seek the ultimate capabilities of organic molecules.”