Optical trap quality in extended 3-D structures built using holographic optical tweezers

摘要

We have recently demonstrated how holographic optical tweezers can be used to build and dynamically manipulate extended 3-D structures. Although successful trapping can be maintained even when a large number of traps are simultaneously manipulated, in general a gradual degradation of trap quality is observed as the number of traps increased. This degradation is partly attributed to the increased 3-D size of the structures. To build and control such large structures the high numerical aperture focusing objective lens has to operate away from its design conjugate for most of the traps, and therefore aberrations will be significant even for high quality objective lenses. A second effect is the decreasing efficiency of the liquid crystal spatial light modulators as they are required to display holograms that contain high spatial frequencies. However these factors do not appear to account fully for the observed weakening of the traps, and it is likely that a reduction of contrast in the trapping optical field also plays an important role. We examine the effects individual optical traps have on each other when they are in close proximity. Techniques that may be used to mitigate the reduced contrast will also be discussed