Fig. 1. (a) Working principle of the proposed design under orthogonal circularly polarized THz beam illumination with spin-selective properties. (b) The assembly process of the metamolecule consists of the stepwise superposition of a pair of HWP meta-atoms with a phase difference of 90°. (c) Four parametric conditions with classical geometric phase modulation, pure phase modulation with spin selectivity, pure amplitude modulation with spin selectivity, and complex amplitude modulation with spin selectivity, respectively.

Fig. 2. (a) Refractive index of high-resistance silicon and wave vectors in the working frequency band. The HWP meta-atoms selected for the organization of the metamolecule, denoted as (b) Meta_1 and (c) Meta_2, have a constant phase difference δ=π/2, respectively. (d) Normalized magnetic field distributions collected within the xoz and yoz planes, respectively, corresponding to a pair of HWP meta-atoms Meta_1 and Meta_2.

Fig. 3. (a) Amplitude and (b) phase delay corresponding to geometric phase modulation obtained by scanning the parameter factor β, including LCP→LCP, LCP→RCP, RCP→LCP, and RCP→RCP channels. (c) GS algorithm flow used to perform THz hologram imaging, (d) target image, (e) processed image. (f) Phase distribution corresponding to the target image. (g) THz hologram images in the LCP→RCP and (h) RCP→LCP channels obtained by utilizing the time-domain solver.

Fig. 4. (a) Sample I obtained by utilizing the ICP etching technique when α = π/4, β = 0, and γ = 0. (b) THz TDS system for performing sample measurement tasks. (c) Simulation and (d) experimental results of transmitted polarization conversion for two spins when α = π/4, β = 0, and γ = 0. (e) AT spectra containing both simulation and experimental results. (f) Amplitude, (g) phase delay, and (h) AT parameter corresponding to spin-dependent pure phase modulation obtained by scanning the parameter factor β.

Fig. 5. (a) Spiral phase distributions embedded in the Z₁=5 mm and Z₂=7 mm planes. (b) Sample II obtained by utilizing the ICP etching technique. (c) Simulation and (d) experimental results extracted in different planes along the propagation direction, including the electric field intensity and phase distribution. (e) THz near-field detection system for capturing the focal field distribution. (f) The mode purity calculated in the Z₁ and Z₂ planes, respectively.

Fig. 6. (a) Amplitude and (b) phase shift corresponding to spin-dependent pure amplitude modulation obtained by scanning the parameter factor β. (c) The extracted amplitudes within the LCP→RCP channel and the calculated AT parameters at intervals of Δβ = 9°, respectively. (d) Top view of the six metamolecules selected for performing pure amplitude shaping. (e) The electric field distribution |E_RL| corresponding to THz near-field imaging extracted over a finite distance from 1.2 mm to 1.5 mm along the z-direction.

Fig. 7. (a) Amplitude and (b) phase shift corresponding to spin-dependent pure amplitude modulation obtained by scanning the parameter factor β, including LCP→LCP, RCP→LCP, LCP→RCP and RCP→RCP channels. (c) Sample III and Sample IV obtained by utilizing the ICP etching technique. (d) Electric field distribution at the focal plane of the assembled meta-lens when β is equal to 0° and 90°, respectively, including simulation and experimental results. (e) Normalized amplitude profiles extracted at the focal plane along the x-direction, corresponding to Sample III and Sample IV.