LLNL materials scientist Tayyab Suratwala knows a thing or two about finishing optics.
Suratwala’s new book, Materials Science and Technology of Optical Fabrication, captures advances from the Laboratory’s quest in the past several decades, as well as progress by others in the field, to develop advanced optics—especially laser damage-resistant optics.
"This is the culmination of a 15-year journey to unwind the mysteries and complexities of the fascinating field of optical fabrication," he said.
Suratwala, program director for Optics and Materials Science & Technology in the NIF & Photon Science Directorate, wrote the book to share the materials sciences aspects of optics fabrication (grinding and polishing) essential to manufacturing the next-generation laser optics successfully used in NIF and other high-energy laser systems. The same techniques are also applicable to other optics, such as those in advanced imaging and spectroscopy systems.
After learning how the surface finishing and processing of optics affected their laser damage and optical performance, "the Laboratory made an investment, largely for the needs of NIF, to understand the science of finishing," Suratwala said. Optics damage results when tiny surface flaws, called damage precursors, begin to grow when hit by intense laser beams and ultimately can render the optic unusable.
"We were at the right place at the right time," he said. "There was a strong need, and fabrication science was still in its early stages. It was an opportunity to turn what was largely an art form (grinding and polishing optics) into more of a science."
There were significant technological benefits as well.
"We got better optics," he said, "and now we’re able to operate NIF at 1.8 megajoules (of ultraviolet light) routinely—and more. At the same time there also have been spinoff benefits in the optics industry."
Suratwala’s book begins by describing the complex interactions that occur during the grinding and polishing process involving the optic. "These interactions affect the major properties of an optic—its roughness, its overall shape, the rate at which you remove material, and the level of surface damage or contamination that you might get as a result of the process," he said.
The book’s second half covers the techniques, tools, and characterization methods that can improve both understanding and the fabrication process, such as fractography—why optics break during fabrication; "scratch forensics"—determining the causes and providing guidelines for repairing surface fractures, such as scratches; and novel ways of characterizing the optic’s response during polishing.
Improving Optical Performance
"All these things that we’ve learned—the fundamental chemistry, physics, mechanics, tribology (friction, lubrication, and wear), and colloidal chemistry—end up not only aiding in making more damage-resistance optics, but also help in improving the optical performance, such as wavefront and low scatter," Suratwala said. "The optics industry loves what we›re doing because it can help them."
Suratwala often is invited to give presentations to technicians and process engineers at major optics manufacturing companies. The Laboratory is hosting an American Precision Optics Manufacturers Association (APOMA) technical workshop at the Garré Vineyards on Oct. 18 and 19, where the book will have a targeted audience.
Suratwala credited the Laboratory Directed Research & Development (LDRD) program for supporting much of the content and his LLNL Mid-career Award with providing support to write the book. He thanked Lab researchers Rusty Steele, Mike Feit, Phil Miller, and Lana Wong "who have supported this work throughout" as well as the many co-researchers, collaborators, and mentors who helped along the way. He also thanked reviewers and graphic artists Margaret Davis, Brian Chavez, and James Wickboldt.
Looking ahead, Suratwala noted that optical fabrication research will continue and grow in new directions.
"We are very interested in taking conventional optical fabrication and turning it into much more complicated-shape optics, which is referred to as freeform optics," he said. "That and additive manufacturing of optics are the future. Many of the book’s fundamentals can be utilized to help build the R&D in this new direction.
"It’s not over, there’s more to do," he said. "This new scope will hopefully lead to the next book in the coming decades."
Materials Science and Technology of Optical Fabrication is published by John Wiley & Sons, Inc., and the American Ceramic Society. Click here for more information.
