Fig. 3

Light-driven periodic angular oscillations of colloidal particles. a Frames from a polarizing optical microscopy video (Supplementary Movie 4) showing oscillation of a micro-platelet within an angular range <180° in a 7 µm cell at low intensity of blue excitation light. Frames A and C show the micro-platelet at the two extreme angular displacements. Images were taken under parallel polarizers (white double arrows). Polarization direction of the blue excitation light (marked with a blue double arrow) is along the far-filed director n₀. b Oscillation frequency as a function of the optical excitation power of blue light delivered to such a particle. c Frames from a polarizing microscopy video (Supplementary Movie 5) showing oscillation of a micro-platelet in a 4 µm cell under white light illumination. Frames A and C depict the micro-platelet at the extreme angular displacement. Images were taken using crossed polarizer and analyzer in the polarizing microscope, with an additional 530 nm retardation plate inserted between polarizers after the sample. Orientation of crossed polarizers and the quarter-wave plate’s slow axis are shown with crossed white arrows and a yellow double arrow, respectively. Note that white light was used here as both the imaging and excitation light source and its polarization P_e was also set to be along n₀. d Oscillation frequency as a function of the optical power of white light. Scale bars are 5 µm. Data points in b and d are mean ± s.e.m; red lines are for eye guiding