Fig. 1. (a) Schematic showing the phase difference introduced at the defocus position where d > 0. A plane wave is transformed to a spherical wave after being focused by a lens; the thickness of the silver film is h = 200 nm, and the inset displays a unit of paired Λ-shaped apertures. (b) Details of the Λ-shaped apertures on sliver film with parameters l = 150 nm, w = 60 nm, and θ = π/4; green arrows indicate the polarization direction of the scattered light.

Fig. 2. (a) Variation of the scattered light’s PCP on d > 0 defocus positions for r₁ = 2000 nm and s = 250 nm. (b) Variation of the scattered light’s PCP on d < 0 defocus positions for r₁ = 2000 nm and s = 250 nm. The black dashed lines indicate the defocus positions predicted by Eq. (2). (c) Variation of the scattered light’s PCP with r₁ and s at the defocus position of d = 5000 nm. (d) Variation of the scattered light’s PCP with r₁ and s at the defocus position of d = −5000 nm. The PCP is computed by the FDTD method, taking the extremum values within the range −0.05 ≤ (k_x² + k_y²) / k₀² ≤ 0.05.

Fig. 3. (a) Top view of the spiral curve with arm numbers of m = +1, 0, −1 from top to bottom. (b)–(d) Simulated scattered light’s intensity, PCP, and phase distribution at d = +5000 nm and d = −5000 nm defocus positions. The phase distribution corresponds to the E_x component, and the NA of the collection lens is set to 0.2. (e) Simulated RCP and LCP intensity profiles and their spatial overlap at k_y = 0. The incident light is radially polarized, which is required to excite the desired scattering characteristics of the spiral structure.

Fig. 4. (a) Scanning electron microscope (SEM) images of the spiral curve with arm numbers of m = +1, 0, and −1 from top to bottom. (b), (c) Measured scattered light’s intensity and PCP distribution; NA = 0.2. (d) Self-interference pattern of the scattered light.