A common method for aligning a telescope in a laboratory setting is to place an interferometer at the focal plane and a return flat in collimated space. For some long wavelength systems that need to be aligned, or checked in the field, transporting an interferometer and a large flat are not practical. One example is a balloon borne terahertz telescope. In this paper, we present an alignment approach that does not require an interferometer or return flat. Instead of using a traditional approach, we are proposing the use of deflectometry and the sine condition test to determine the state of alignment. Both of these tests can be done with the same equipment which primarily consists of a camera and an LCD larger than the clear aperture of the telescope. Deflectometry is used to measure defocus, spherical, and on axis coma while the sine condition test measures linearly field dependent astigmatism. These are the low order aberrations that will be affected by misalignments, and their magnitudes and orientations can be used to align the system. We explain how this approach is used, show the results of simulations, and predict the expected performance of a telescope aligned with this approach.
Reconfigurable freeform optical systems enable greatly enhanced imaging and focusing performance within nonsymmetric, compact, and ergonomic form factors. In this paper, several improvements are presented for the design, test, and data analysis with these systems. Specific improvements include definition of a modal G and C vector basis set based on Chebyshev polynomials for the design and analysis of non-circular optical systems. This framework is then incorporated into a parametric optimization process and tested with the Tomographic Ionized-carbon Mapping Experiment (TIME), a reconfigurable optical system. Beyond design, a reconfigurable deflectometry system enhances metrology to measure a fast, f/1.26 convex optic as well as an Alvarez lens. Further improvements in an infrared deflectometry system show accuracy around λ/10 of the notoriously difficult low-order power. Working together, the mathematical vector polynomial set, the programmatic optical design approach, and various deflectometry-based optical testing technologies enable more flexible and optimal utilization of freeform optical components and design configurations.
The Scanning Long-wave Optical Test System (SLOTS) is a slope measuring deflectometry system that provides accurate measurements on ground surfaces. As it uses a thermal source, we can measure an optic during the grinding phase which allows us to correct figure errors when material removal is much faster. We have made improvements in SLOTS, such as the step-and-stare method, the ceramic rod, and the Gaussian fitting processing software, so that this system supports higher accuracy and resolution. As a result, SLOTS is an optical testing system that covers a huge portion of the fabrication process from the grinding to the figuring. It is a complementary solution for other metrology systems such as the laser tracker, SCOTS, and null interferometry. SLOTS can reduce the manufacturing time by producing ground aspheres that have low errors of the surface figure when polishing begins.