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LASER 2003: What's hot in Munich this year?

30 May 2003

Brain surgery and gravity-wave detection are just two of the laser applications that Andreas Tünnermann wants to hear more about. Here, the CLEO Europe conference co-chair reveals what he believes will be the hot topics at LASER 2003. World of Photonics.

From LASER 2003. World of Photonics Visitor Magazine

What will be the most exciting technologies presented in Munich this summer? Andreas Tünnermann, a professor at the Institute of Applied Physics in Jena, Germany, is in no doubt. Fibre lasers and applications of ultrafast light sources are at the top of his list.

So what is it about fibre lasers that is provoking so much interest at the moment? "There's been lots of excellent work in the past few years and we are coming to the point where applications for high-power fibre lasers are entering the automotive and printing industries," explained Tünnermann.

The dramatic scaling of output power achieved recently is allowing fibre lasers to tackle commercial applications that were out of reach in the past, he says.

"Power scaling in continuous-wave [CW] operation allows applications in the automotive industry such as welding, while fibre sources that can generate high-repetition-rate short pulses are of interest for three-colour generation in laser displays," said Tünnermann. "Pulsed fibre lasers can now generate picosecond pulses with a repetition rate of tens of megahertz and average powers of 100W or more." In addition, CW fibre-laser systems with output powers of several kilowatts are now commercially available.

As a result, several production processes are starting to embrace fibre-laser technology: "For powers of up to 100W, industrial transfer has already started in applications such as computer-to-plate printing," said Tünnermann. "To date, the writing speed [of the plate] has been limited to the output power of transverse singlemode laser systems. With fibre lasers now operating at 100W or more in single transverse mode you can go faster than any other technology."

Tünnermann says that the key advantage of fibre lasers is their good beam quality at high power. "You have an excellent beam quality because it is defined by the waveguide [fibre] structure," he explained. "This is independent of the output power, which is an advantage compared with any other laser system."

Over the past few years, researchers have been busy designing new types of fibre that are optimized to enhance laser performance. One design that Tünnermann picks out as being especially important is the so-called large-mode-area fibre. "Here you have a singlemode diameter of tens of microns, which reduces nonlinear effects in the fibre. This is important for both CW and pulsed operation."

He is also excited about the potential of photonic-crystal fibre - a strand of silica glass that contains a carefully designed pattern of tiny holes to yield unique optical properties. "This allows you to optimize the fibre not only through the material's composition but also by nanostructuring a special refractive index profile."

Tünnermann says that fibre lasers are likely to find many scientific uses. "They might be used as the light source in the next generation of gravitational-wave detectors. At the moment, conventional end-pumped solid-state lasers are used and the output power of these ultrastable laser systems is limited to about 10W. My group has recently demonstrated more than 100W based on a novel type of fibre amplifier with the same stability as those 10W systems," he said.

There are lots of applications on the horizon for ultrafast lasers, adds Tünnermann. "Particularly in Europe, there has been some remarkable work in the past few years in the fields of biotechnology, life sciences and micromachining," he commented. "We are now seeing several companies think about using these lasers in production. Of course, we have heard that said for years, but my feeling is that very soon we will have some systems that are suitable for industry."

Tünnermann strongly believes that this will lead to "some new real-world applications". "It's not just about drilling holes in metals," he exclaimed. "We are now starting to think about applications that can only be done with femtosecond lasers."

One example is the application of multiphoton absorption. This technique is particularly powerful as it allows materials processing within the interior of a solid. "One idea is writing three-dimensional waveguides in dielectric materials. You fire femtosecond pulses into a glass substrate and move the laser beam with respect to the target to generate structures. This is new and there is no other way to do it. People are also considering brain surgery using the same technique."

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