The effect of a spherical output surface on the performance of a truncated dielectric paraboloid in focusing the light from multiple diode lasers was studied with ray tracing. Especially the effects of the radius and the displacement of the output sphere were investigated. In addition, the performance of a parabolic concentrator with a spherical output surface in high-numerical-aperture focusing of diode laser light was demonstrated experimentally. The 1/e2 diameter of the measured focus was less than 100 μm.
"Focusing diode lasers using a truncated paraboloid with spherical output surface," Optical Engineering 46(5), 054301 (1 May 2007). https://doi.org/10.1117/1.2734993