Further Considerations

Using the techniques described above, we have created triangular and square tweezer arrays which trap up to 400 particles at once. Still larger arrays and less regular arrangements are certainly feasible. Even static holograms permit some degree of reconfigurability. Rotating a hologram about its optical axis rotates the pattern of tweezers in the plane. Tilting it changes the aspect ratio. Individual traps can be turned off by blocking their beams in the plane conjugate to the object plane, labelled OP$^\ast$ in Fig. 1. Such spatial filtering also can be useful for eliminating stray laser light, and to block out any undiffracted portion of the input beam. Replacing lenses L1 and L2 with zoom lenses should permit a degree of continuous scaling of the lattice constant.

The methods described in the previous Sections are appropriate for projecting arrays of identical tweezers in the plane, where each tweezer shares the properties of a single tweezer formed by the unmodulated input beam. Shaping the wavefronts of the individual beams, for example to embed some optical vortices in an array of conventional optical tweezers, requires a straightforward elaboration of the AA algorithm [13]. Creating three dimensional arrays, on the other hand, requires more sophisticated calculations to avoid undesirable interference effects, and will be discussed elsewhere.