Design of freeform lenses for illuminating hard-to-reach areas through a light-guiding system.

Designing freeform optics for illuminating hard-to-reach areas is a challenging and rewarding issue. The current designs of freeform illumination optics are mostly valid in the applications in which the region of interest is easily accessible. What we present here is a general formulation of designing freeform lenses for illuminating hard-to-reach areas. In this method, the freeform lens consists of two elaborately designed surfaces, by which both the intensity distribution and wave-front of the light beam are manipulated in a desired manner. The light beam after refraction by the freeform lens is further guided through a light-guiding system to produce a prescribed illumination on a target plane which is inaccessible. The properties of the light-guiding system are taken into account in the tailoring of the freeform lens profiles to guarantee the prescribed illumination on the target plane. Two examples are presented to demonstrate the elegance of this method in designing freeform optics for illuminating hard-to-reach areas.