Nonimaging optics: optical dcsign at thc thermodynamic limit

Th design mcthods of nonimaging optics for illumination by light sourccs which arc of• finite extcnt arc well cstablishcd1. Two classcs of algorithms havc b2cn found which work at or ncar th2 s2cond—law of thermodynamics limit of prformancc. Th2 first of thsc is the "string" or "cdgc—ray" mcthod. It may bc succinctly characterized as a gcncralization of Fcrmat's principle. While all of imaging optics can in principle be derived from: