Fig. 2

Design procedure of freeform surface. a Illustration of the optimization process of wavefront function φ(x,y) for the DOE to focus the obliquely incident light into a point. b Sketch of the optimization of freeform surface for a point-to-point optical imaging. The direction of light on the left portion is reversed in the actual recording process. c Schematic diagram of the optimization of eight peripheral surfaces to focus obliquely incident light into four points around the sample. d Photo of the fabricated optical surface with main exposure surface and alignment surfaces. All scale bars: 10 mm. a-c are readapted from the rendering results in Code V