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Optical designs for the next generation space science instruments call for unconventional, aspheric, and freeform (FF), prescriptions with tight tolerances. These advanced surfaces enable superior-performance, compact, and lower cost systems but are more challenging to characterize and, hence, to fabricate and integrate. A method was developed to characterize a wide range of optical surfaces, without requiring custom-made correctors, and to align them to each other for a high-performance optical system. A precision coordinate measuring machine, equipped with a non-contact, chromatic confocal probe, was used to measure numerous optics including large convex conics, high-sloped aspherics, several FF surfaces, and grazing-incidence x-ray optics. The resulting data were successfully reduced using custom-developed, advanced surface fitting analysis tool, to determine the optic’s alignment relative to the global and local coordinate systems, surface departure from design, and the as-built optical prescription. This information guided the modeling and the alignment of the corresponding as-built optical systems, including a flight system composed of a three-mirror anastigmat.

We present a general optical design survey of two-mirror unobstructed plane-symmetric freeform (FF) telescopes to provide a standardized framework and reference for further developments in the field of FF optics. We find that there are fundamentally two main design forms: those that use a positive tilt of the secondary and those that employ a negative rotation to achieve the unobstructed condition. Utilizing this survey, results can be categorized into simple groups of two-mirror unobstructed FF telescopes, analogous to the distinction between a Gregorian-type telescope and Cassegrain-type telescope. Allowing FF surfaces in optical design can enable more compact telescopes while potentially improving the image quality and allowing wider fields of view (FOVs). We define a FF optic as a nonrotationally symmetric mirror or lens, typically with large departures from a best-fit spherical surface (many microns or even millimeters). New manufacturing and testing methods have enabled the production of these types of surfaces. The telescopes we present maintain a 4 ∶ 1 aspect ratio of the FOV and utilize X–Y polynomials for mirror surface description. We impose a plane symmetric constraint on the system and an accessible entrance pupil. We generate charts documenting the relationship between FOV and F / # for the presented optical design forms. We also compare our results to a baseline rotationally symmetric system. These results provide a general method of evaluating baseline designs for two-mirror unobstructed FF telescopes.

Space-based observation of gravitational waves promises to enable the study of a rich variety of high energy astrophysical sources in the 0.0001 to 1 Hz band using signals complementary to traditional electromagnetic waves. Gravitational waves represent the first new tool for studying the sky since gamma ray telescopes debuted in the 1970s, and we expect compelling science to be the result. The fundamen- tal measurement is to monitor the path length difference between pairs of freely falling test masses with laser interferometry to a precision of picom- eters over gigameter baselines. The test masses are arranged in an equi- lateral triangle to allow simultaneous measurement of both gravitational wave polarizations. The heliocentric orbital space environment enables the test masses to be shielded from large ground motions at low frequen- cies, and allows the construction of long measurement baselines that are well matched to the signal wavelengths. Optical telescopes play an impor- tant role in the measurement because they deliver laser light efficiently from one spacecraft to another. The telescopes are directly in the meas- urement path, so there are additional performance requirements to sup- port precision metrology beyond the usual requirements for good image formation. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10 .1117/1.OE.52.9.091811)