Fig. 2: Experimental evidence of optical magnetic field-associated trapping of Si nanoparticles.
From: Optical trapping with optical magnetic field and photonic Hall effect forces
a Schematic representation of the microscope objective that is employed to generate a tightly focused azimuthally polarized beam for trapping Si nanoparticles in a water filled chamber. The closeup schematic of the focused beam (at the top) shows a Si nanoparticle at the trapping plane of the azimuthally polarized beam, with arrows indicating the longitudinal and azimuthal polarization of Hz (blue) and E (red), respectively. b SEM micrograph of a drop-cast Si nanoparticle that coincidentally has the same dimensions as the trapped one shown in (c). c Dark-field microscopy image of a representative Si nanoparticle with a diameter of 205 nm trapped at the center of the focused azimuthally polarized beam delineated by the white dashed circle. d The size of the Si nanoparticle shown in (c) is determined by comparing the particle’s in-situ measured scattering spectrum (upper panel) with calculated Mie scattering spectra (lower panel; calculated in a water environment) and adjusting the Si nanoparticle size in the simulations until their scattering spectral signatures align, including the multi-pole modes. The red dashed vertical line indicates the trapping laser wavelength. The inset is a color dark-field microscopy image of the specific 205 nm dia. Si nanoparticle. e Nanoscale localizations of three representative Si nanoparticles with different sizes overlaid with their measured trapping beam profiles as gray-scale background. The upper and lower rows exhibit the experimental and GLMT-Langevin dynamics simulation results, respectively. The scale bars in the experimental images are 720 nm. f The radial position distributions associated with the experimental (upper) and simulation (lower) results of (e).
