University of Rochester

Scientists' Work Named Best of Year by Optical Society

March 6, 2001

A new way to measure aspherical optical surfaces, a design for off-axis telescopes, and a more cost-effective way to weed out optical manufacturing errors have earned year-end kudos for several teams at the University of Rochester. Three research groups at the University's Institute of Optics were honored by the Optical Society of America for conducting outstanding research in 2000.

Thomas Brown, associate professor of optics; Duncan Moore, Rudolf and Hilda Kingslake Professor of Optical Engineering; and Paul Murphy, a former optics graduate student currently at QED Technologies, Inc., were cited for developing a more accurate and cost-effective way to measure aspherical optical surfaces, components that are cut in other-than-spherical shapes. Typically, to measure an aspherical optical component, such as the Hubble Space Telescope's primary mirror, additional optics are needed to essentially turn the aspherical characteristics to spherical ones, which can be measured more easily. Accurate measurements are needed to ensure that the element meets specifications and works properly; the failure to accurately measure the Hubble mirror, for instance, resulted in a defect that degraded the telescope's ability to resolve distant objects. The University team learned how an interferometer, which is used to measure such optical elements, introduces errors of its own. With this new knowledge, such errors can now be corrected for with computers, giving engineers a look at the real surface of the element.

Bryan Stone, assistant professor of optics, and graduate student Richard Youngworth worked toward more accurate tolerancing of optics-a practice of determining which deviations in an optical element's design are acceptable and which are not. To find the balance between various types of deviations, engineers employ a standard method of weighing each kind of manufacturing error and correcting so that the most significant ones are less likely to occur. In optical systems, however, the standard method doesn't work as well as it could, leading to unnecessary errors. The University team has devised a new way to "weigh" the different errors and so manufacture more accurate optics from the same machines.

Joseph Howard, a recent graduate currently at NASA, and Bryan Stone determined the rules that govern off-axis optical designs. Regular, large telescopes use on-axis designs, in which a large mirror reflects light up to a smaller mirror that is housed above it, partly blocking the path of incoming light. Off-axis design puts the secondary mirror off to the side, out of the light path, so that the main mirror can collect all the available light unobstructed. The design uses spherical mirrors, which are much easier and cheaper to produce than the parabolic mirrors currently used for such applications. The design could lead to telescopes and other optical devices that are more sensitive, yet cheaper to produce.