Electromagnetic Spin-Orbit Interactions via Scattering of Subwavelength Apertures

Circularly polarized electric fields incident on subwavelength apertures produce near-field phase singularities with phase vorticity $\pm 1$ depending on the polarization handedness. These near-field phase singularities combine with those associated with orbital angular momentum and result in polarization-dependent transmission. We produce arbitrary phase vorticity in the longitudinal component of scattered electric fields by varying the incident beam and aperture configuration.

Figure 1

Numerically calculated (a) amplitude and (b) phase of the scattered longitudinal-field component produced by a left-handed or ${\sigma }_{+}$ circularly polarized plane wave incident on a square metal aperture of length $L=\lambda$ and thickness $D=\lambda /2$.

Figure 2

The reconstructed amplitude and phase of scattered longitudinal-field components produced by (a)–(b) square and (c)–(d) round apertures in aluminum film when illuminated with an incident circularly polarized field with wavelength $\lambda =500\mu \mathrm{m}$. The aperture width and radius are $200\mu \mathrm{m}$. The aluminum has a thickness of $80\mu \mathrm{m}$.

Figure 3

Amplitudes and phases of the longitudinal-field component produced by Laguerre-Gaussian beams of topological charge $m_0=+1$ and (a)–(b) left-handed circular polarization and (c)–(d) right-handed circular polarization incident on square aperture $L=\lambda$ and thickness $D=\lambda /2$. The dotted lines outline the incident mode field.

Figure 4

Difference in transmission between orthogonal circularly polarized vortices $\Delta T=(T_{+}-T_{-})/(T_{+}+T_{-})$ as a function of normalized hole aperture size for different incident topological charge $m_l$. (a) Theoretical prediction given a round aperture in an infinitely thin metal sheet. (b) Numerical calculation for a square aperture given finite sheet thickness $D=\lambda$. Note: graphs use different scales.

Figure 5

(a, d) Two- and four-aperture configurations with dimensions and separation $L=2/3\lambda$. (b),(e) Amplitude and (c),(f) phase of the corresponding scattered-field longitudinal components via numerical calculations. The metal sheet has thickness $D=\lambda /4$. The dotted lines outline the incident mode field.