Optically-Induced Crystals of Sub-Micron Particles
While optical lattices have long been used to create fully controllable crystals in ultracold atom experiments, we have only recently applied them to trapping larger particles. In this talk, I will present the first optical lattice for large (sub-micron) particles. Four 1064 nm optical-tweezing beamswith a common focus interfere to form a 3D periodic trapping potential. Thousands of polystyrene particles of diameter ~200 nm are trapped, forming a 3D, defect-free crystal.
The trapping geometry shows strongpolarization dependence; we see unexpected 3D ordering even in polarizationcases that should provide only 2D potentials. The lattice is observedthrough both direct imaging and Bragg scattering with a 532 nm probe beam. The Bragg scattering patterns are consistent with the calculated trapping geometries. The decay and rise of the Bragg scattering intensity upon switching the lattice off and on reveals the Brownian motion dynamics of the particles in the periodic optical trapping potential. Experimental results agree well with results from trajectory simulations based on the Langevin equation.