Figure 1

(a) Schematic illustration of the experimental optical setup. The 820-nm polystyrene spheres are optically bound in a tractor beam (λ₀=532 nm, incident angle α=2.15 °, S-polarization, green beam) and illuminated using a 1064-nm laser (red beam), which is utilized for holographic video microscopy. The wavevector diagram illustrates direction of the incident (k₁) and reflected (k₂) beam. (b) Typical sequence of recorded hologram images of two optically bound particles with the subtracted hologram background (see Supplementary Media 1 for the full movie). Dashed line marks the beam center z=0. (c) Time dependence of positions of two optically bound particles in z and y axis shown in b, where λ_m=400 nm is the tractor beam wavelength in an aqueous medium, and the beam is centered at z=0. The orange or turquoise background corresponds to the pushing or pulling regime, respectively. The right images visualize the relative configurations of the particles at two selected moments marked by dashed lines. Red crosses highlight important points that interconnect experimental data with numerical calculations shown in Figure 3a. For more details, see Methods and Supplementary Information.