Abstract
In this paper we demonstrate controlled loading of a closely packed array of optical traps. We also describe the technical advantages of our method of filling the trap array (which makes use of an independent, steerable trap created by a separate objective lens), as well of our specific implementation of array generation by multi-beam interference. Microscopic polystyrene spheres are trapped and subsequently assembled into sites on a two-dimensional optical lattice, which is formed from the interference of two pairs of coherent laser beams via an optical setup that allows for simple, continuous variation of lattice parameters over a very wide range. Individual particles in the initial assembly are dynamically manipulated with the independent laser beam, which offers the freedom to generate either defect-free lattices or a lattice with designer defects. As examples we demonstrate the assembly of a defect-free square lattice and a lattice with a single vacancy.
Highlights
In the work reported here, we combined single particle manipulation and reconfigurable, 2d optical interference trapping to make 2d colloid patterns with ‘designer’ features
A standing wave produced by the interference of two coherent laser beams has a spacing given by d = λ/[2 sin(θ/2)], where λ is the laser wavelength, and θ is the angle between the two beams
When two parallel, collimated laser beams, symmetrically displaced with respect to the lens axis, are incident on a lens, they too will meet at the focal point and generate a standing wave in the vicinity of the beam waists, with a spacing governed by an angle θ that depends on the focal length and the separation of the two beams
Summary
In the work reported here, we combined single particle manipulation and reconfigurable, 2d optical interference trapping to make 2d colloid patterns with ‘designer’ features. B3 and B4, the beams in the second pair, have identical path lengths, which may differ from that of the first pair; they form a vertical standing wave. The colloidal spheres are pushed against the cover glass on the far side of the beam by the radiation pressure; the gradient force associated with the optical lattice traps the spheres at this surface on the intensity maxima.
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