German research targets diode lasers

FIGURE 1. Eight high-power diode lasers with trapezoidal resonators are each 3 mm long but with a different angle design. The width of the laser output facet (bottom) varies from right to left (twice each) 200, 300, 400, and 500µm. With this design, a continuous-wave output of more than 2.4 W with high beam quality (M2

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FIGURE 1. Eight high-power diode lasers with trapezoidal resonators are each 3 mm long but with a different angle design. The width of the laser output facet (bottom) varies from right to left (twice each) 200, 300, 400, and 500µm. With this design, a continuous-wave output of more than 2.4 W with high beam quality (M2 <2) has been achieved from a single diode laser.

Although diode lasers havecaptured a large share of the market related to telecommunications and optical data storage, they have yet to make a major dent in industrial manufacturing applications-especially the automotive stronghold of conventional Nd:YAG and carbon dioxide (CO 2) lasers. This may soon change if the German laser industry has anything to say about it.

German laser firms have long been major players in the world market for industrial lasers. Their strong emphasis on manufacturing applications has been influenced by early innovators in the field, such as Baasel Lasertech (Starnberg), Lambda Physik (G?ttingen), and Rofin-Sinar (Hamburg), as well as government initiatives. Unlike in the USA, German state-supported research programs, such as the ongoing Laser 2000 project, often have a two-pronged emphasis-basic research and applications-related development.

Last year alone, German firms captured 40% of the worldwide market for manufacturing of laser-beam sources, revenue-wise. This wasn`t the case, however, in the considerably larger market for lower-power diode lasers. Especially in applications such as barcode reading, optical storage, and telecommunications, US and Far Eastern diode-laser manufacturers continue to dominate the market relatively unchallenged.

The problem-at least for the Germans-is that diode lasers are also gaining importance as sources for manufacturing. In line with this trend, the quest for survival is driving the efforts of leading German manufacturers to develop powerful diode lasers and exploit their manufacturing potential.

The situation may not be as bad as some fear. While a catch-up game may be necessary in diode-related research, this is not the case for the required support technologies. German firms have a good grounding in technologies such as microelectronics to control laser emission, micromechanics to set up diode laser bars and stacks, and micro-optics to shape and collimate the beam. There also is an established network of research institutions-as well as ready access to a global source of high-power diode lasers, namely Siemens (Regensburg).

As with earlier research efforts, a major thrust of the diode-related laser research will most likely be to expand the applications base. The reason is simple-the more applications there are, the higher the lot sizes of laser devices, which will lower both manufacturing costs and end-unit prices. Successful widespread infiltration into traditional manufacturing applications would be doubtful, otherwise.

Expanding research

Still under the umbrella of Laser 2000, the Germans are establishing two new projects. The first is called NOVALAS, which translates as innovative laser systems based on high-power diode lasers. Its predominant emphasis will be on R&D. The second project-Modular Diode-Laser Systems (MDS)-will explore new applications, as well as optimization of existing technology.

NOVALAS research will have five basic target areas:

1. High-power diode-laser technology leading to 1-kW stacks with high beam quality, also vertical-cavity surface-emitting laser (VCSEL) arrays emitting between 800 and 1060 nm.

2. Micro-optics and micro-optical components for high-power diode lasers.

3. Diode lasers for materials processing, including re search into combining the stacks to produce several kilowatts of power, coupling to optical fibers, and coherent coupling.

4. Fiber lasers and power scaling.

5. Diode-pumped solid-state lasers in the multikilowatt power range, as well as compact systems and disk lasers.

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FIGURE 1. Eight high-power diode lasers with trapezoidal resonators are each 3 mm long but with a different angle design. The width of the laser output facet (bottom) varies from right to left (twice each) 200, 300, 400, and 500µm. With this design, a continuous-wave output of more than 2.4 W with high beam quality (M2 <2) has been achieved from a single diode laser.
Click here to enlarge image

NOVALAS will involve a network of cooperating universities and, to a more-limited extent, companies such as CeramOptec, Dilas, Freiberger Compound Materials, Jenoptik, and Siemens. The Fraunhofer Institute for Applied Solid-State Physics (Freiburg, Germany)-which already has generated innovative results from earlier Laser 2000 projects-will coordinate the program (see Fig. 1).

Total annual expenses for the diode-laser R&D are estimated at DM 20 million ($12.1 million) over 4.5 years-with just 48.5% of that amount funded by the Federal Ministry for Education, Science, Research, and Technology (BMBF). Because this funding level is relatively low compared to the ambitious scale of the project, strong coordination of activities will be required. The challenge will be to fully exploit microtechnology for the realization of powerful diode-laser stacks.

Successful project organization will also demand rapid information exchange. While members of each section will meet twice a year, they will stay in continuous contact via an intranet. Members from all groups will also meet annually and participate in standardization and patent committees, as well as special working groups. Information will also be disseminated via an Internet Web site with both a public and a password-protected institutional domain (www.novalas.fhg.de).

Manufacturing maneuvers

Unlike NOVALAS, industrial firms are predominant members of the MDS project, which is also supported by the German BMBF. The goal of MDS is to identify the requirements and then develop diode lasers suitable for materials-processing tools for manufacturing industries.

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FIGURE 2. The goal of the MDS project is to shift the curve for diode lasers into the application realm of CO2 lasers and solid-state lasers.
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Diode lasers are extremely compact and maintenance-free and feature an overall efficiency of about 50%-which Rofin-Sinar engineers point out is significantly higher than that of conventional CO2 or Nd:YAG lasers. The problem is that the beam quality and related focusability of current diode technology still restrict industrial applications to surface treatment and soldering and welding of plastics and thin sheetmetal. Key targets of the MDS project will thus be improvements in beam quality and laser output power, as well as the development of new application areas (see Fig. 2).

The project, which will be led by Rofin-Sinar GmbH, will involve 14 other firms and six institutions. Anticipated to last five years, it will have a total budget of more than DM 75 million ($45.3 million), with BMBF providing about 46% of funding.

The team`s strategy will be to divide its focus into three subgroups-chip technology, laser system technology, and application technology. Roughly a quarter of the project efforts will be devoted to semiconductor technology, another quarter to systems technology, and half to applications. In this way, the team intends to maintain a close coupling between laser technology and the requirements of production technology that will extend across the entire chain from semiconductor technology for the generation of power lasers and the microtechnology for stack packaging to full-system equipment and standardization.

This industrial effort will have a symbiotic relationship with NOVALAS, which will feed its results related to diode-laser development to the Modular Diode-Laser Systems project. Conversely, the MDS project group will feed information on its mounting and packaging experience to NOVALAS.

FIGURE 2. The goal of the MDS project is to shift the curve for diode lasers into the application realm of CO2 lasers and solid-state lasers.

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