Fig. 1. Categories, related properties, phenomena, and application fields of optical angular momentum

Fig. 2. Spin angular momentum density and momentum density in circularly polarized propagating plane waves^[114]. (a) Instantaneous electric and magnetic fields during the propagation of circularly-polarized m=i plane wave,where Er,t=ReEre-iωtandHr,t=ReHre-iωt; (b) orbital momentum density (blue vector arrows) and spin momentum density (orange vector arrows)

Fig. 3. Evanescent wave generated by total internal reflection has a transverse spin angular momentum density^[12]. (a) Spin angular momentum density distribution of evanescent wave in transverse magnetic mode,the inset shows z-evolution of instantaneous electric and magnetic fields E and H for x-polarized light; (b) the generated evanescent wave with a transverse spin angular momentum density S ^e,m when the polarization direction is ± 45°

Fig. 4. Transverse spin angular momentum density generated by interference of two linearly polarized propagating plane waves, the illustrations correspond to the changes in electric and magnetic fields along the z-axis at different x positions^[12]

Fig. 5. Spin-momentum locking properties of structural evanescent fields^[15]. (a) Direction of spin angular momentum density determined by wave vectors; (b) direction of spin angular momentum density determined by the curl of energy flux density

Fig. 6. Schematic of several typical near-field optical probes and a spin angular momentum detection system based on NSOM. (a) Aperture probes formed by cutting off the top of metal coating on optical fibers using a focused particle beam^[153]; (b) scattering near-field probe^[154]; (c) cone glass probe with gold nanoparticles attached to the tip^[151]; (d) side wall aperture probe for measuring near-field optical frequency components^[155]; (e) experimental optical setup for detecting near-field spin angular momentum distribution using NSOM system, quarter-wave plate and linear polarizer are used to extract the left and right circularly biased components^[103]; (f) experimental results obtained from the experimental optical path shown in Fig. 6(e), the configuration of the incident beam is a radial first-order vortex beam^[103]

Fig. 7. Nanoparticle-film structures for the detection of spin angular momentum. (a) Two excitation methods of nanogold particle-gold film structure^[156]; (b) optical response of PS nanoparticles^[102]; (c) Ag core-Si shell probe particles used for detecting magnetic field components and the electromagnetic response curves of the particles^[91]; (d) schematic of the coupling process between tightly focused beam and nanoparticle waveguide structure and Fresnel coefficients for different modes in this structure^[104]

Fig. 8. Spin angular momentum detection system based on nonlinear effects. (a) Optical path configuration of nonlinear near-field optical microscopy^[99]; (b) circular coupled grating structure for exciting SPP^[99]; (c) near-field distribution obtained by illuminating the grating with left-handed and right-handed circularly polarized pump beams and their differential result

Fig. 9. Spin angular momentum detection system based on PEEM. (a) Schematic of the coupling of circularly polarized light to a grating^[86]; (b) vector diagram of the structure of optical skyrmion and longitudinal and in-plane components of the structure of optical skyrmion^[86]; (c) schematic of the coupling of linearly polarized light to an Archimedean helix grating^[88]; (d) plasmonic meron SAM texture^[88]

Fig. 10. Precision measurement of graphene's optical conductivity by photonic spin Hall effect^[35]. (a) Photonic spin Hall effect at an air-graphene interface; (b) experimental setup to detect the tiny spin-orbit interaction of light in graphene; (c) amplification of pointer shifts as a function of the postselected angle β; (d) measurement of the optical conductivity in the unit of σ0 for monolayer, bilayer, and trilayer graphene

Fig. 11. Spatial differentiation demonstration at a tilted polarizing interface^[39]. (a) Schematic of the experimental setup for observing splitting beams based on quantum weak measurement, the insets correspond to spatial differentiation results for a Gaussian illumination with the inclination angle θ=45°; (b) measurement of the spatial spectral transfer function at a tilted polarizing interface; (c) detailed data of the transfer function extracted from Fig. 11(b)

Fig. 12. Microscopic imaging experiment on quantitative-phase-microscopy targets^[40]. (a) Experimental setup for photonic spin-Hall differential microscopy, the insets are SEM images of a 350 nm focus star on the resolution target; (b) photograph of the phase target; (c) relationship between the horizontal-direction intensity of five edge images and the phase gradient of five focus-star targets; (d) images of targets 1-5 selected from user report for quantitative-phase-microscopy target; (e)(f) bright-field and differential images of quantitative-phase target; (g) intensity curves corresponding to the white lines across the edge images in Fig. 12(f)

Fig. 13. Experimental setup and sample characterization in the metasurface quantum edge detection^[37]. (a) Experimental setup of metasurface quantum edge detection; (b) photograph of partial metasurface sample, and scale bar is 4 mm; (c) polariscopic analysis characterized by crossed linear polarizers of the sample area marked in Fig. 13(a), the blue bars indicate the orientation of rotated nanostructures in one period, which represents the Pancharatnam-Berry phase induced by the laser writing dielectric metasurface, and scale bar is 50 m; (d) SEM image of sample area marked in Fig. 13(c)

Fig. 14. Experimental schematic and effect of edge detection based on phase gradient metasurface^[38]. (a)-(p) Edge detection images with various resolutions at the wavelength of 500 nm; (q) two separated LCP and RCP beam components when PB phase gradient metasurface is illuminated by collimated LP beam; (r) phase gradients of LCP and RCP component; (s) Fourier space spectrum and (u) real-space image of a square object; (t) Fourier space spectrum and (v) real-space image when a PB phase gradient metasurface is added at the Fourier plane, blue- and red-shaded areas indicate the resultant edge information along the PB phase gradient direction

Fig. 15. [in Chinese]

Fig. 16. Generation and application of optical lateral forces^[18]. (a)-(c) Experimental frames of trapping-detrapping-trapping of a cholesteric liquid crystal particle by switching the light polarization; (d)-(l) experimental demonstration of the bidirectional enantioselective separation of a micro-sized cholesteric liquid crystal particle; (m)(n) optical lateral force on the chiral particle in a linearly polarized evanescent wave

Fig. 17. Optical lateral forces in different beams and the spin motion of particles under their influence. (a)-(d) Lateral force and spin torque distributions in the focal plane illuminated by vector vortex beams with topological charges (a)(b) m=4 and (c)(d) m=-4^[169]; (e)-(h) spin and orbital motion of the particle illuminated by circularly polarized vortex beams with topological charges of (e) m=5 and (g) m=-5, and by radially polarized vortex beams with (f) m=5 and (h) m=-5^[170]

Fig. 18. Metarobots based on optical lateral forces. (a) One-dimensional metarobot which can move bilaterally with different helicity of light^[171]; (b) one-dimensional linear metarobot by optical lateral force on a plasmonic nanoantenna, allowing the moving resolution to be beyond the diffraction limit^[172]; (c) two-dimensional metarobot excited by both linear and circularly polarized light^[173]; (d) three-dimensional light-driven microdrones using two overlapping light waves with two wavelengths^[174]

Fig. 19. Spin angular momentum applied to precision displacement sensing^[29]. (a) Illustration of the structured spin texture in a skyrmion-pair; (b) theoretical results of the spin distribution obtained from the Richard-Wolf theory; (c) experimentally measured structural spin distribution; (d) typical characteristic sensing curve from the central region

Fig. 20. Optical spin-orbit coupling effect applied to magnetic domain detection^[30]. (a) Schematic for the generation of a optcal skyrmion in a ferromagnetic material on the example of SPP excited on a surface of a thin (50 nm) Co film by a tightly focused (NA=1.49) radially polarized beam; (b)(c) spin states of positive and negative skyrmions generated with l=±1 right-handed polarized light with Co magnetization in +z direction; (d)(e) spatial distribution of Δγs for the skyrmions in ±z directions; (f)(g) spatial distributions of Δγs for the magnetic structure consisting of two domains with opposite magnetization orientations