Fig. 1. Schematics of the experimental setup for the all-optical metallic-particle trap. (a) Particles may be trapped at two positions located in front of and behind the focus plane. (b) Detailed experimental setup of the entire system. Gold particle diameters vary from 1.0 to 5.0 μm. L, lens.

Fig. 2. Forces exerted on gold particles. (a) Axial forces acting on particles of different radii at different points on the optical axis. The focus plane is at z=0. (b), (c) Transverse components of the optical force along the x and y axes, respectively, for various planes along the z-axial direction. Balance (F=0) is achieved at the crossing point of a curve with the abscissa. The gold particle diameter is 2.5 μm in (b) and (c); the 532 nm laser beam is x-directional polarized with a trapping power of 20 mW, in accordance with experimental conditions.

Fig. 3. All-optical manipulation of Au particles of different diameters trapped using a linearly polarized 532 nm laser beam. Black crosses indicate the position of the focused beam; blue and yellow arrows indicate the positions of the reference particles for calibration. Particle diameters range between 1.0 and 5.0 μm: (a) ∼1.5  μm, (b) and (d) ∼2.5  μm, and (c) ∼3.5  μm. The scale bar (black line in lower far-right corner) has length 5.0 μm.

Fig. 4. Axial components of forces exerted on the gold particle (diameter of 2.5 μm) located at the optical axis with (a) linear, (b) radial, and (c) azimuthal polarizations. Beams of wavelengths 532, 1064, and 1550 nm were applied, each with a trapping power of 20 mW.

Fig. 5. Transverse components of force exerted on a gold particle (diameter of 2.5 μm) located at the trapping plane in front of the focus with different polarizations and wavelengths. The open symbols and dotted lines represent the forces acting on the particle located at the plane of z=−1.8  μm, and the solid symbol and line are those on the plane of z=1.5  μm. Trapping power is 20 mW.

Fig. 6. Dynamic all-optical manipulation of Au particles using beams of different polarizations and wavelengths. (a) Radially polarized 532 nm laser, (b) azimuthally polarized 532 nm laser, (c) radially polarized 1064 nm laser, and (d) linearly polarized 1550 nm laser. A jump is observed in (c). Black crosses indicate the positions of the focused beam, blue and yellow arrows indicate positions of the reference particles for calibration. The Au particles in the experiments have diameter of ∼2.5  μm. The scale bar (black line in lower far-right corner) is of length 5 μm.