Luque A
Appl Opt. 1980 Jul 15;19(14):2398-402. doi: 10.1364/AO.19.002398.
In this work we analyze a two-stage concentrator in which the first stage is reflective and the second stage considers the first one as a Lambertian source in order to obtain the highest possible gain. We determine the profile and the position of this first stage, which happens to be a parabola, and we calculate the value of the gain as a function of the acceptance angle and the focal length of the first stage.