Using an optical lattice formed by four laser beams, we obtain three-dimensional light-induced crystals of 490 nm diameter polystyrene spheres in solution. The setup yields face-centered orthorhombic optical crystals of a packing density of about 40%. An alignment procedure is developed in which the crystals are first prepared near a sample wall, and then in the bulk of the sample. A series of tests is performed that demonstrate particle trapping in all three dimensions.For one case, the trapping force is measured, and good agreement with a simple theoretical model is found. Possible applications are discussed.

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