Researchers have created a mirror out of diamond, one of the strongest materials on the planet. The researchers created a highly reflective mirror by etching nanostructures onto the surface of a thin sheet of diamond. The mirror withstood experiments with a 10-kilowatt Navy laser without being damaged. The researchers envision these mirrors being used in defense applications, semiconductor manufacturing, industrial manufacturing, and deep space communications in the future.
Since 1970, nearly every car, train, and plane has been built with high-power lasers that fire a continuous beam of light. These lasers are strong enough to cut steel, precise enough to perform surgery, and powerful enough to send messages into deep space. They are so powerful, in fact, that it’s difficult to engineer resilient and long-lasting components that can control the powerful beams the lasers emit.
Most mirrors used to direct the beam in high-power continuous wave (CW) lasers today are made by layering thin coatings of materials with different optical properties. However, if there is even a minor flaw in any of the layers, the powerful laser beam will burn through, causing the entire device to fail. If a mirror could be made from a single material, it would significantly reduce the likelihood of defects and increase the laser’s lifespan. But what material would be strong enough?
Our one-material mirror approach eliminates the thermal stress issues that are detrimental to conventional mirrors formed by multi-material stacks when irradiated with high optical powers. This method has the potential to improve or develop new applications for high-power lasers.
Marko Loncar
Now, researchers at Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS) have created a mirror out of diamond, one of the strongest materials on the planet. By etching nanostructures onto the surface of a thin sheet of diamond, the research team built a highly reflective mirror that withstood, without damage, experiments with a 10-kilowatt Navy laser.
“Our one-material mirror approach eliminates the thermal stress issues that are detrimental to conventional mirrors formed by multi-material stacks when irradiated with high optical powers,” said Marko Loncar, the Tiantsai Lin Professor of Electrical Engineering at SEAS and the paper’s senior author. “This method has the potential to improve or develop new applications for high-power lasers.”
The findings were published in Nature Communications. The technique for etching nanoscale structures into diamonds was developed by Loncar’s Laboratory for Nanoscale Optics for applications in quantum optics and communications.
“We thought, why not use what we developed for quantum applications and use it for something more classical,” said Haig Atikian, a former graduate student and postdoctoral fellow at SEAS and first author of the paper.
The researchers sculpted an array of golf-tee shaped columns on the surface of a 3-milimeter by 3-milimeter diamond sheet using this technique, which uses an ion beam to etch the diamond. The shape of the golf tees, which are wide on top and skinny on the bottom, makes the diamond’s surface 98.9 percent reflective.
“You can make reflectors that are 99.999 percent reflective, but they have 10-20 layers, which is fine for low power lasers but not for high powers,” said Neil Sinclair, a research scientist at SEAS and co-author of the paper.
The team turned to collaborators at the Pennsylvania State University Applied Research Laboratory, a Department of Defense designated U.S. Navy University Affiliated Research Center, to test the mirror with a high-power laser.
The researchers placed their mirror in front of a 10-kilowatt laser, strong enough to burn through steel, in a specially designed room that was locked to prevent dangerous levels of laser light from seeping out and blinding or burning those in the adjacent room.
The mirror emerged unscathed.
“The selling point of this research is that we had a 10-kilowatt laser focused down into a 750-micron spot on a 3-by-3-millimeter diamond, which is a lot of energy focused down on a very small spot, and we didn’t burn it,” said Atikian. “This is important because, as laser systems become more power hungry, you need to come up with creative ways to make the optical components more robust.”
The researchers envision these mirrors being used in defense applications, semiconductor manufacturing, industrial manufacturing, and deep space communications in the future. The method could also be applied to less expensive materials such as fused silica.
