Design and Metrology of Optics for Telescopes and Sunlight Concentration

Abstract

The principles of optical and metrology design form the foundation for technologies in many areas. Of interest to this dissertation are the areas of solar energy and telescopes. For solar energy, low quality (~1 mrad) solar disk images are formed for the purposes of photovoltaic or heat energy production. For space and ground telescopes, high quality (0.1-1.0 μrad) stellar images can be formed, especially over wide fields where phenomena such as dark energy can be further studied. There are 3-4 magnitudes of difference in precision between solar energy and telescopes, and yet similar optical and metrology design principles are applicable.Concentrated solar energy can be used to exploit the benefits of high efficiency Photovoltaic Multi-Junction cells (CPV). The design of these optics is largely driven by the cost per watt of generation. Pupil-imaging techniques help with mispointing and low tolerance alignment of optical components. Several designs will be covered in detail, exploring their benefits and limitations. The cousin to CPV, Concentrated Solar Power (CSP) is of special interest. Industry standards involve usage of tens of thousands of heliostats focusing sunlight on a central "power tower" at ~500X solar concentration. Concave focusing heliostats are of limited value, they suffer from spillage of sunlight around the tower receiver due to changing astigmatic aberrations as the sun angle changes. We have designed and built a prototype that uses active bending astigmatic modes in a 1.6 m2 heliostat mirror, demonstrating sharp disk images of the Sun formed from 0 degree angle of incidence to >70 degree angle of incidence with >90% ensquared energy into an area little larger than the disc image. With ~10X concentration only hundreds of heliostats are needed to achieve ~1000X. Optical and metrology design are further applied to another metrology system for a 1.6-m gull-wing lens, which is part of a recent design for a wide field 6.5-m Cassegrain telescope. The telescope design is intended as a future replacement for DESI, acting as a spectrometer for ~10,000 stellar objects simultaneously. The gull-wing lens is a key component for the telescope achieving ~0.5 arcsecond resolution for a 3.0-degree field of view for 365 nm - 950 nm wavelengths. Several other telescope designs are presented, including a ground telescope with 10,000 m2 of area that can achieve 300,000X spectroscopic resolution for the oxygen band. This makes possible the search for life on exoplanets. Another design is presented that pushes resolution and field of view to the very limits of a 20-m space telescope with ~0.01 arcsecond resolution (at 1 μm wavelength) and a 1-degree field of view. A new class of telescopes with an analytical solution are presented, the Double-Cassegrain.