Of all optical components, the mirror comes closest to creating an alternate world. If constructed precisely enough, a flat mirror can display what appears to be reality behind it, fooling eyes and optical instruments alike. While few refractive lenses exist that are aberration-free across a large field, such a property is natural for an uncurved mirror. By adding curvature to a mirror (and putting thoughts of alternate realities aside), an imager can be made that has a property foreign to refractive lenses—full achromatism. Curved mirrors have another property that is of great importance: they remove the burden of focusing light from refractive materials, freeing designers to create imaging optics that function at wavelengths blocked by refractive substances, as well as high-power and high-energy laser optics that handle powers and energies damaging to transmissive lenses.
The design, fabrication, and use of mirrors in optical systems have produced an accumulation of lore separate from that for refractive optics. How to specify a mirror, how to make it, and how to use it are all questions that have been answered in many different ways over the years—a result of diverse paths of research, development, and application.
These three articles present some of this hard-earned knowledge. In the first article, David Collier and colleagues detail what it takes to properly specify a high-reflection coating for a laser mirror, concentrating on how to prevent laser damage, how to maintain low coating stress and thus high flatness, and how not to overspecify a mirror coating. The second feature, by Michael McKinney and coworkers, examines the technology of diamond turning for metal mirrors, first outlining existing techniques, and then describing a recently developed augmentation to two-axis diamond turning that creates a three-axis technique able to machine nonrotationally symmetric mirror surfaces. The concluding article, by Phillip Mitchell and others, explains how fast-steering mirrors correct for vibration and other causes of laser-beam misalignment.
John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.