Modular Assembly of Metamaterial Using Light Gradient Force in Standing Wave Optical Trap

The feasibility of assembling metamaterial using the light gradient force of a Standing Wave Optical Trap (SWOT) was studied in this work. When time-shared across a 2D lattice, SWOT creates a 3D array of traps, which were then populated with monodispersed metallic and dielectric Nanoparticles (NPs). The NPs were then anchored in position by a photopolymerized hydrogel scaffold creating a single voxel. The voxels were then stitched together using a step-and-repeat method to produce metamaterials of any size or shape. To stiffen structure, the hydrogels were then vitrified using Tetraethyl Orthosilicate (TEOS). Optical performance of the metamaterials was analyzed using cross-polarized reflection spectroscopy. The results shows that the mean separation of NPs along the optical axis is 322 nm, for 860 nm trapping laser, which is close to separation between successive antinodes of the standing wave in the water (λ_trap/2n_water). The registration error within the voxels (σ=55<!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>σ=55 nm) was limited by the Brownian motion, while the error between the voxels (σ=88<!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>σ=88 nm) was limited by the repeatability of the microscope stage. Finally, compared to Gaussian beam, a pseudo-Bessel beam produced a larger and more regular array along the optical axis due to its longer focal length and shorter healing distance.