An analysis was performed to determine the radiation transmitting characteristics of a circularly reflecting duct with a collimated beam of rays entering at one end. Data were obtained for various angles of beam incidence, duct included angle, and ratios of the radii of the two walls. Both the over-all energy transmitting characteristics and the local energy absorption distribution were determined.
Curtis A. Rhodes, "Transmittance Properties of a Curved Specularly Reflecting Duct Irradiated by a Collimated Beam," Appl. Opt. 6, 1767-1772 (1967)