21 Apr 2006
The output of a single laser diode has been held below 10 W or so by adverse thermal effects and materials limitations. Now Alfalight is commencing a multi-million dollar project to develop a 50 W diode.
Alfalight of the US has been awarded $4.7 million by the US Defense Advanced Research Projects Agency (DARPA) to develop and commercialize a 50 W single emitter laser diode.
This 18-month project, which is part of DARPA's Architecture for Diode High Energy Laser Systems (ADHELS) program, is intended to produce the means for a multi-kilowatt diode laser system. Alfalight plans to develop devices capable of generating near-diffraction-limited output power of 50 W per emitter. Such devices would be suitable building blocks to combine into a multi-kilowatt direct-diode laser.
The company says that the contract has an additional nine-month follow-on option, which could result in a total potential value of at least $6.1 million.
"Diode lasers are attractive for various industrial and military applications because of their output power, reliability, efficiency and low cost," Manoj Kanskar, VP of Research and Development at Alfalight told optics.org. "The ADHELS program will enable us to overcome the last remaining hurdle for this technology, which is to improve the beam quality at high power operation. This improvement is planned to be by a factor of 10 compared to today's typical broad area lasers."
"The goals of this program are to develop and manufacture industry-leading, high-performance commercial diode lasers," adds Mohan Warrior, president and CEO of Alfalight. "For this program, our team will develop a device design with fundamentally improved beam quality compared with current multimode laser designs. We believe these performance improvements will be highly valuable in next-generation direct-diode systems and defense applications."
Previously, so-called broad area laser diodes have been widely available with powers up to 8 W. In January 2006, at Photonics West, Alfalight demonstrated a prototype 22 W version. But with a broad area laser, that output may be approaching the upper limit for such a structure.
"To revise our laser diode design to enable an output up to 50 W will mean a broader beam with the goal for emission to be as near to diffraction-limited radiation as possible," says Ron Bechtold, VP marketing and sales.
"The contract calls for development of a single emitter that produces 50 W output power; the chip size should be similar to today's devices although the actual size will be determined by the development work.
"We anticipate that the diode will have a similar sized cavity but the laser will emit through a larger surface area. This will allow us to achieve more power and brightness around the same 980 nm wavelength."
The company expects wide commercial applications for such diode lasers. Historically, deployment of direct diode laser systems has been limited to functions such as soldering, brazing and plastic welding, because the beam has not been bright enough to take the laser system beyond niche applications.
A high power direct diode laser system may displace YAG lasers in applications such as welding and metal cutting. Defense-related industries are also looking for more portable systems for applications such as anti-missile systems or for destroying unexploded ordnance. The diode laser is attractive because it requires less electrical power and occupies a smaller footprint.
The DARPA contract will initially see Alfalight to develop the 50 W single-emitter technology for DARPA's own purposes but the terms of the deal will allow the company to commercialize the laser for other purposes.
"The timeline we have is 18 months", says Bechtold. "I would expect to see commercial samples by early 2008 and a marketable product in 2009. We estimate that the market for high powered multimode laser diodes is worth at least $200 million and we are also expecting to see the market grow significantly in the next five years.
Problems to solve
There are two main problems that have prevented previous laser diode designs from achieving higher powers: thermal roll-over and optical mirror damage. Thermal rollover is when heat builds up in the cavity disrupting the lasing process.
Optical mirror damage can be caused by stray aluminum III strands in the lasing facet, which cause localized heating. Alfalight's new approach avoids the problem of higher power beam emergence from a ragged crystal face.
Another important consideration is the likely lifetime of such a high power laser diode. The contract calls for 50W to be demonstrated though it does not specify a reliability requirement.
Bechtold expects the initial commercial product based on this technology to deliver around 25 W with industrial level reliability - either similar to today's products on the market or better. The output power for the commercial device is then expected to move towards 50 W as product development continues.
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