Lasers can be used to apply forces to microscopic particles, affording a non-contact method for manipulation of matter. Optical tweezers utilize a tightly focused laser beam to confine a particle in three dimensions. Thermal gradients (generated by heating a thin layer of gold with a laser) can induce the formation of colloidal crystals, which can act as an analogue of nanocrystal growth. We use optical tweezers to control the growth and learn about interactions.
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