Transparency-switching optical element for sun tracking applications

We present a novel optical element that behaves as a dynamic aperture capable of tracking a moving light source. The element is based on a composite material which when heated undergoes reversible transition from an opaque to transparent state, resulting from a phase transition in one of its components that modifies the microstructure of the material. The material has been designed to undergo a localized transparency transition at the point of illumination by a focused beam, activated by the absorption and conversion to heat of a portion of the incident light. As a result of this mechanism the aperture reactively tracks a moving light spot, such as that created by focusing sunlight onto a surface during the suns apparent motion through the sky. Such an element has been proposed as a solution to the sun tracking problem of solar concentration, as it allows admission of sunlight into a concentrating light trap over a wide range of solar angles.