Holographically corrected telescopes

Abstract

ABSTRACT Holographic correction oflow-quality telescopes is an inexpensive method of obtaining large aperture devices suitable forlidar, imaging, and directed energy weaponry. We present an analysis oftwo different methods for producing diffraction-limited telescopes from the holographic correction of spherical mirrors. These evaluations are essential for choosing theoptimal design for a given telescope application. Included in our discussion are the results from preliminary experiments intothe various designs. The aim ofthe project is construct the first ever holographically corrected astronomical telescope forboth ground and space-based operations.Keywords: Holography, telescopes, aberrations, next generation space telescope. 1. INTRODUCTION Large diameter telescopes are required for many high-resolution imaging and light-gathering applications. As imagingdevices, telescopes are useful in both ground and space-based operations, and in all cases a larger primary diameter results ineither improved resolution and/or the amount oflight gathered. The cost oflarge ground based telescopes is large due to thetechnical challenges involved in maintaining perfect figure quality over a large area. Added to this is the problem ofatmospheric turbulence, which although easily controllable for small apertures, is still a major problem for extremely largediameter telescopes. One solution is to place the telescope in orbit, but the costs involved in fabricating perfect primary andensuring an undistorted figure after launch and deployment are large. For a next generation optical space telescope withdiameters >4m, new technologies wifi be required. One possible solution is to use an inexpensive, low-quality mirror whichis holographically corrected in situ to diffraction-limited performance. In the future, such technology should make it possibleto construct the next generation space telescope for a fraction ofthe cost that present schemes allow.Holographic correction ofaberrated optical elements was developed separately by Upatnieks et a!'. and Kogelnik andPennington2. Denisyuk and Soskin3 and later Munch et al.4'5 showed how this technology could be applied to the correctionof aberrated telescope primaries. These experiments relied primarily on a collimated illumination source, which requiredeither a perfect optical element ofthe same diameter as the one to be corrected, or a point source of light an infmite distanceaway. A feasible compact design was developed by Andersen et al.8 in which a point source oflaser illumination is situatedat the center of curvature ofthe mirror. In this paper, we build extend this work with the aim ofdeveloping the firstholographically corrected telescope to be used for actual astronomical imaging.