Fig. 4: Focal points along a double-cycle cylindrical helix.
From: Multifaceted control of focal points along an arbitrary 3D curved trajectory
a The schematic diagram of the super metalens M3 for generating 200 focal points along a double-cycle continuous 3D cylindrical helix with constant pitch and radius. The longitudinal separation is 1 µm, which makes the total length of the curved trajectory equal to 200 µm. The first and last focal points are located at z = 300 µm and z = 499 µm, respectively. b The 3D view of the spiral shape with a constant pitch and a constant radius. c The simulation and measured results of the intensity distributions of selected focal points (1st, 50th, 100th, 150th, and 200th) under the illumination of RCP incident light beam at corresponding operating wavelengths (501, 550, 600, 650, and 700 nm) and longitudinal distances (300, 349, 399, 449, and 499 µm). The dashed yellow curved path shows the antinodes of the y-axis along the longitudinal distance. It is used to indicate the positions of the generated focal points at the desired locations in 3D space
