Optical comparison of two-stage reflection systems based on ASAP

Four types of two-stage reflection systems were compared, of which the secondary mirror was an ellipsoidal, a hyperboloidal, a planar or a paraboloidal type, respectively. A paraboloidal dish with a diameter of 1000 mm and a rim angle of 60° was employed as a primary mirror in each system. The final concentrated spots were on the vertexes of the dishes in ellipsoidal and hyperboloidal systems. As to the ellipsoidal system, the flux density on the receiver increases when numerical aperture (NA)<0.4 and then decreases. The spot size decreases with NA increasing. The maximum flux concentration ratio is about 5000× at NA=0.4. As to the hyperboloidal system, both the flux density and spot size decrease with NA increasing. The maximum flux concentration ratio is about 8990× at NA=0.5. The ellipsoidal and hyperboloidal systems are applicable to cases which need low concentrated spots, and the latter has a higher flux concentration ratio with a more compact structure and a smaller secondary mirror. As to the planar system, with the relative location of the concentrated spot increasing, the flux density increases and spot size changes less obviously. The maximum flux concentration ratio is about 21000×. A planar secondary mirror is suitable for a system which needs a high concentrated spot. As to the paraboloidal system, with relative location of the secondary mirror increasing, the flux density increases and spot size decrease. The maximum flux concentration ratio is 80×, which is the lowest among systems mentioned above. A paraboloidal secondary mirror is suitable for a system that requires low concentration ratio.