Fig. 1. Schematic diagram of plasmonic tweezers. The phase of circularly polarized light is modulated by the hologram loaded onto the SLM. A 2D Fourier relationship can be delineated between the complex amplitude along an annular-rings coupler of a converging surface wave and the out-of-plane component of the SPP field. The red arrow indicates the movement of the hotspot, and the gold particles move accordingly.

Fig. 2. Analytical and numerical simulation results for various target patterns. (a) Target patterns with hotspots in different positions. (b) Normalized two-dimensional field intensity distributions corresponding to the different target patterns calculated directly by the custom-refined FT algorithm; (b1)–(b3) are the corresponding two-dimensional field distributions of (a1)–(a3), accordingly. (c), (d) Full-wave 3D-FDTD simulation results of normalized intensity and phase distributions of numerical simulation results for the different target patterns; (c1)–(c3) are the intensity distributions of numerical simulation results matched with target patterns (a1)–(a3), accordingly. (d1)–(d3) correspond to the phase distributions of numerical simulation matched with target patterns (a1)–(a3), accordingly. (e1)–(e3) Phase distributions of the incident beam tailored with different target patterns (a1)–(a3), accordingly. The scale bar is 4 μm.

Fig. 3. (a) Intensity distribution of electric field of a single dot hotspot (background). The blue arrows denote the energy flow distributions (Poynting vector) at each position. (b) Optical force (represented by the blue curve) exerted on a gold particle (diameter of 1 μm, located 50 nm above the surface of gold film) and optical potential well (represented by the red curve) along the x axis. The black dot represents the experimental results. The horizontal axis measures the distance from the center of the gold particle to the central peak of the SPP field. The data for both the optical force and the potential well were smoothed using the piecewise cubic Hermite interpolating polynomial (PCHIP) method. (c) The lower part of the figure shows the magnitude of the optical force exerted on the gold particle at various locations, while the upper part of the figure displays the distribution profile of the corresponding potential well in the XY plane. The scale bar is 2 μm. The incident power is 10 mW.

Fig. 4. Schematic diagram of the experimental setup. (a) Experimental configuration of the plasmonic tweezers system. Inset: the hologram loaded on the spatial light modulator (SLM) consists of a modulated phase pattern and a blazed grating with a ring-shaped aperture pattern. Abbreviations: L1 and L2, lens; P, polarizer; HP, half-wave plate; SLM, spatial light modulator; QP, quarter-wave plate; OBJ, objective lens; BS, beam splitter; CCD, charge coupled device. (b) Scanning electron microscopy image of the nanostructure. The innermost ring has a radius of 10 μm, the linewidth of each ring is 240 nm, and the spacing between the two adjacent ring slits is 786 nm (λspp). The scale bar is 4 μm.

Fig. 5. Experimental demonstration of plasmonic tweezers. (a) Sequential images show the capture and manipulation of gold particles (diameter of 0.8–1.5 μm) forming an “S” shape. (b) Sequential images depict the capture and manipulation of gold particles resulting in a “Z” shape. (c) Sequential images illustrate the capture and manipulation of gold particles achieving a “U” shape. The blue dashed line represents the trajectory of the particle motion. The sequence of images progresses from left to right, with a time interval of 1 s between images. The incident laser power is 10 mW. The scale bar is 4 μm.