Long Depth of Focus of Metalens
We placed a arcylic plate away from the lens and watched the focused beam spot on the acrylic.
(1) When we use a normal focal lens (flat-convex), the spot diameters change much when moving the acrylic away from the focal lens. The movement range is 20mm only but the beam diameter obviously changes.
(2) When we use a metal lens, the spot diameters almost do not change when moving the acrylic away from the meta lens. The movement range is 120mm but the beam diameters do not obviously change.