(color online) Schematic layout of the image mapper. We establish the – coordinate to illustrate the image mapper structure. The substrate plane of the image mapper lies on the plane. The axis is parallel to the length of the strip mirror. Panel (a) shows a 3D model, which has only eight strip mirrors for clarity (in a practical system, the image mapper usually contains hundreds of strip mirrors). The mirrors are grouped into two blocks and each block contains four mirrors with different 2D tilt angles (α_m, β ), where , 2, and , 2. The mirror tilt variations are periodically repeated in different blocks. Panel (b) shows an illustration of the definition of (α_m, β ). Here, the vector is introduced as the normal of a strip mirror. The tilt angle between and the plane is represented by α_m, and β_n is the tilt angle between and the plane.