Virtually every car, train and plane that has been built since the 1970s has been manufactured using powerful lasers that emit a continuous beam of light. These lasers are strong enough to cut steel, accurate enough to perform operations, and powerful enough to carry messages into deep space. In fact, they are so powerful that it is difficult to create elastic and durable components that could control the powerful rays emitted by lasers.
Today, most mirrors used to direct a beam in high-power continuous (CW) lasers are made by applying thin coatings of materials with different optical properties. But if in any of the layers there is at least one, tiny defect, a powerful laser beam will burn out, causing the whole device to fail.
If a mirror could be made of a single material, it would greatly reduce the likelihood of defects and increase the life of the laser. But what material will be strong enough?
Now researchers from the Harvard School of Engineering and Applied Sciences John A. Paulson (SEAS) have built a mirror from one of the strongest materials on the planet: diamond. After etching the nanostructures on the surface of a thin sheet of diamond, the research team built a high-reflectivity mirror that withstood without damage experiments with a 10-kilowatt Navy laser.
“Our single-material mirror approach eliminates thermal stress problems that damage conventional mirrors formed by stacks of multiple materials when irradiated with high optical powers,” said Mark Loncher, SEAS professor of electrical engineering Tiancai Lin and senior author of the paper. “This approach has the potential to improve or create new powerful laser applications.”
The study is published in The nature of communication.
The Lonkara Nanoscale Optics Laboratory originally developed a technique for etching nanoscale structures into diamonds for application in quantum optics and communication.
“We thought about why not use what we’ve developed for quantum applications and use it for something more classic,” said Hague Atikyan, a former graduate student and graduate student at SEAS and the first author of the paper.
Using this technique, which uses an ion beam to etch a diamond, the researchers sculpted an array of golf-shaped columns on the surface of a 3 by 3 millimeter diamond sheet. The shape of the golf tees, wide at the top and narrow at the bottom, makes the diamond surface chop 98.9%.
“You can make reflectors that reflect 99.999%, but they have 10-20 layers, which is good for a low-power laser, but certainly won’t withstand a lot of power,” said Neil Sinclair, SEAS researcher who authored the article.
To test the mirror with a high-power laser, the team approached staff from the Laboratory of Applied Research at the University of Pennsylvania, Department of Defense, designated by the U.S. Navy University Research Center.
There, in a specially designed room that is closed to prevent the tracking of dangerous levels of laser light and blinding or burning those in the next room, the researchers placed their mirror in front of a 10-kilowatt laser strong enough to burn steel. .
The mirror came out undamaged.
“The highlight of this study was that we had a 10-kilowatt laser focused on a 750-micron spot on a 3 by 3 millimeter diamond, and that’s a lot of energy focused on a very small point and we didn’t burn,” – said Atikyan. “This is important because as laser systems become more and more energy-intensive, you need to come up with creative ways to make optical components more reliable.”
In the future, researchers believe that these mirrors will be used for protective applications, semiconductor manufacturing, industrial production and communications in outer space. The approach can also be used in less expensive materials such as fused silica.
Harvard OTD protects the intellectual property associated with this project and explores the possibilities of commercialization.
The study was co-authored by Pavel Latovets, Xiao Xiong, Srujan Misala, Scarlett Gauthier, Daniel Vinz, Joseph Randy, David Berno, Sage DeFrance, Jeffrey Thomas, Michael Roman, Sean Darant and Federico Capas, Professor Robert Robert L. Wallace from Professor Robert L. Wallace. Applied Physics and Senior Research Fellow in Electrical Engineering at SEAS Vinton Hayes.
This study was conducted in part at the Center for Nanoscale Systems (CNS), a member of the National Coordinated Infrastructure Infrastructure Network (NNCI), supported by the National Science Foundation under the NSF No. 1541959. Partly supported by the Air Force Research Office (MURI, grant FA9550-14-1-0389), the Agency for Advanced Research Projects in Defense (DARPA, W31P4Q-15-1-0013), the Center for Integrated Research STC Quantum Materials and the NSF Grant № DMR-1231319.