Experimental study of the first telescope with a toroidal curved detector

We describe a practical implementation of the anamorphically curved detector concept. To demonstrate its advantages, a telescope lab prototype was developed, built, and tested. It is based on a four-mirror all-spherical unobscured design, similar to that proposed by D. Shafer. The telescope is open at F/#=5.5, and its extended field of view is 10.6 deg× 8 deg. We explore the design parameter space to demonstrate the change in gain introduced by the curved detector and to substantiate the chosen parameters. If the image surface is curved to the shape of a toroid, the image quality reaches the diffraction limit over the entire field by design. The design was optimized to use standard concave spherical mirrors. The detector was curved down toroidally with an exquisite surface precision of ≈11-μm peak-to-valley. The experimental tests of the prototype have shown that the use of the toroidally curved detector allows to increase the contrast in the field corner by ≈0.3 units, which is in good agreement with the modeling results. We also propose a few prospective applications of the demonstrated concept.