Three-dimensional optical trapping with a low-NA objective using a flat-top beam.

In this study, we demonstrate a novel optical setup that is capable of volumetric 3D trapping and crystal-like structure generation. We achieved this by shaping asymmetric counter-propagating beams comprised of a flat-top beam on one side and a multifocal spot on the other. Here, we study this trapping system both experimentally and theoretically and demonstrate stable trapping. Unlike most previous techniques, here we use low numerical aperture optics resulting in long manipulation distances and a wide field of view for side and front microscopy of the sample chamber. Moreover, the setup is easy-to-align and less sensitive to misalignments compared to most 3D structure forming methods. Our system can find application in the development of novel materials and microscopy studies on trapped particles.