Volumetric imaging of holographic optical traps

The holographic optical trapping technique creates arbitrary three-dimensional configurations of optical traps, each with individually specified characteristics. Holographic modification of the individual traps' wavefronts can transform conventional point-like optical tweezers into traps with different structures and properties, and can position them independently in three dimensions. Here, we describe a technique for rapidly characterizing holographic optical traps' three-dimensional intensity distributions. We create volumetric representations by by holographically translating the traps through the optical train's focal plane, acquiring a stack of two-dimensional images in the process. We apply this technique to holographic line traps, which are used to create tailored one-dimensional potential energy landscapes for mesoscopic objects. These measurements highlight problems that can arise when projecting extended traps with conventional optics and demonstrates the effectiveness of shape-phase holography for creating nearly ideal line traps.