(color online) The schematic diagram for processing perpendicularity of mirror 2 or 3 as seen in Fig. 1 with (a) the three-dimensional view and (b) the front view. The ULE mirror is mirror 2 or 3 in Fig. 1. Two fused silicon blocks are auxiliaries used for optical machining. Angle 1 shows the perpendicularity of mirror 2 or 3. Surface A is the plane to be polished and bonded to mirror 1. Surface C will be the reflecting plane of the hollow CCR. The green light is the laser beam from the ZYGO interferometer to measure angle 2.