Boeing’s Thin Disk Laser Breakthrough
The possibility of having laser weapons on the battlefield is now much closer to reality thanks to Boeing’s announcement that its thin disk laser has achieved ground-breaking levels of efficiency and beam quality. This achievement builds off of years of research into using solid state lasers instead of larger chemical lasers for military applications. The viability of using solid state lasers as weapons is steadily increasing. The main problem is that as the power of the laser goes up, the size of the laser also increases. Improving the efficiency of solid state lasers is crucial to minimizing their size.
A thin disk laser is a type of solid state laser, which is very different from a chemical laser. It doesn’t use hazardous chemicals or gases, such as chlorine gas, as the laser gain medium but instead uses a crystal material that is doped with a rare earth element. A thin disk laser specifically uses a gain crystal that is a thin disk. This disk usually has a thickness measured in hundreds of micrometers with a diameter in millimeters or centimeters. The disk is mounted to a heat sink on one side to remove the excess heat. Other less powerful lasers, also referred to as pump lasers, are directed at the disk which excites the particles and produces the final laser beam. Boeing SVS based in Albuquerque, New Mexico, USA has been conducting research into increasing the power and efficiency of thin disk lasers.
During the summer of 2013, Boeing’s thin disk laser demonstrated groundbreaking efficiency and beam quality in front of the Department of Defense, who set the requirements of the program. The laser’s power output was 30 percent higher than project requirements and also exceeded laser beam quality requirements. Beam quality is basically a measure of how tightly a laser beam can be focused. It is commonly measured by M2, which indicates how close a given laser beam is to a single mode beam. While Boeing hasn’t publicly stated the laser’s exact output numbers, the beam power was 30-kilowatts. It is also very efficient for a laser at around 30 percent. Boeing has achieved this efficiency by designing a system that reduces the effects of optical aberrations inherent in thin-disk designs. This system uses adaptive optics to essentially “cancel out” these optical impurities. They are on track to achieving the U.S. government’s desired output of 100kW at high efficiency.
The first major attempt to weaponize high energy lasers was with the Boeing Airborne Laser Testbed. This consisted of megawatt-class Chemical Oxygen Iodine laser (COIL) mounted in a Boeing 747. It was designed to shoot down ballistic missiles while in their boost phases. It successfully shot down two missiles during tests. The project was cancelled in 2011 due to the impracticality of the system. One major drawback of the Airborne Laser (ABL) was the immense size and weight of the system. COIL lasers are inherently very large and this one was no exception. Each unit of the ABL’s laser system was the size of an SUV. The defense industry is now using solid state lasers due to their much smaller size. These weapons can fit onto ships and trucks. Unfortunately they are still very inefficient and still require a great deal of space.
The thin disk laser that Boeing is using for testing is currently very large. It takes up several large optical benches and uses commercial off-the-shelf Trumpf lasers as pump lasers. One goal will be to scale the laser down to fit onto smaller platforms such as the Army’s High Energy Laser Mobile Demonstrator System (HE LMD). HEL MD is incorporated onto a military Oshkosh truck and currently houses a 10-kilowatt laser.
Solid state laser technology is constantly improving and Boeing is at the forefront. Laser weapons offer the ability to be much more precise at longer ranges than conventional weapons. The main obstacles to be overcome are efficiency and size. We will continue to see tactical lasers fit into smaller packages as they become more efficient. Lasers have already been mounted in Humvees and may soon be able to be carried by individual soldiers. The battle space of the future will heavily utilize laser weapons.
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- USAF Airborne laser, Accessed 30 October 2013.