Double-tailored imaging concentrators

We present a new approach in optical design whereby two-stage axisymmetric reflectors are tailored with a completely imaging strategy, and can closely approach the thermodynamic limit to radiation concentration at near-maximum collection efficiency. Practical virtues include: a) an inherent large gap between the receiver and the second-stage mirror; b) an upward-facing receiver: c) the possibility of compact units (large rim angles), i.e., low ratios of total depth to total width; and d) no chromatic aberration. We describe how one can tailor both the primary and secondary mirrors so as to insure that spherical aberration is eliminated in all orders, and circular coma is canceled up to first order in the angle subtended by the radiation source. An illustrative solution that attains about 93% of the thermodynamic limit to concentration is presented for a far-field source, as is common in solar energy and infrared detection applications. Double-tailored imaging concentrators are similar in principle to complementary Cassegrain concentrators that comprise a paraboloidal primary mirror and the inner concave surface of a hyperboloid secondary reflector, but have monotonic contours that are substantially different with far superior flux concentration.