EXTRACTING CONCENTRATED GUIDED LIGHT

The maximum concentration of radiation is proportional to the square o f the refractive index of the medium in which it propagates. A medium with a high refractive index can also serve as a Lightguide for concen trated radiation. However, if concentrated radiation is extracted from one medium, with a high refractive index, to another, whose index is lower (e.g., from fused silica into air), part of the radiation may be lost because of the total internal reflection at the interface. We pr esent polygonal shapes suitable for efficient extraction of the concen trated radiation in a controllable way, without increasing the cross-s ection area (or diameter) of the Lightguide. It is shown analytically and experimentally that the use of a secondary concentrator, followed by such a Light extractor, both having a high refractive index, can pr ovide considerably more power to a solar receiver with a specific aper ture. (C) 1997 Optical Society of America.