Optical efficiency of a refractive secondary concentrator

Refractive secondary concentrators are being considered as an optical component in solar thermal power and propulsion systems. To evaluate the impact of a refractive secondary concentrator on the overall efficiency of the optical system, the optical efficiency of an acrylic refractive secondary concentrator prototype was evaluated on an optics bench. Light from a laser was allowed to enter the refractive secondary concentrator from a variety of positions, and an integrating sphere was used to collect the exiting light. Energy output of the refractive secondary concentrator was compared to energy input. Several mathematical models were used to describe potential flux distributions impinging on the front surface of the refractive secondary concentrator. For uniform illumination, the optical throughput was found to be 0.874. Different flux profiles resulted in optical throughputs in the range of 0.857 to 0.889. An antireflective coating added to the refractive secondary concentrator should increase optical throughput further.