Angle dependent condensing efficiency of Winston cone in terahertz region

The condensing performance of Winston cone has been examined in the optical and terahertz (THz) regions by geometrical and wave optics simulations and the measurement of visible light. We have confirmed that the Winston cone possesses a sharp cutoff of incidence angle in condensing efficiency as expected; however we have found the condensing efficiency decreases at around normal incident, which is due to many times of reflection losses inside the condenser.