Simultaneous optical trapping and imaging in the axial plane: a review of current progress

Optical trapping has become a powerful tool in numerous fields such as biology, physics, chemistry, etc. In conventional optical trapping systems, trapping and imaging share the same objective lens, confining the region of observation to the focal plane. For the capture of optical trapping processes occurring in other planes, especially the axial plane (the one containing the z-axis), many methods have been proposed to achieve this goal. Here, we review the methods of acquiring the axial-plane information from which axial plane trapping is observed and discuss their advantages and limitations. To overcome the limitations existing in these methods, we developed an optical tweezers system that allows for simultaneous optical trapping and imaging in the axial plane. The versatility and usefulness of the system in axial-plane trapping and imaging are demonstrated by investigating its trapping performance with various optical fields, including Bessel, Airy, and snake-like beams. The potential applications of the reported technique are suggested to several research fields, including optical pulling, longitudinal optical binding, tomographic phase microscopy (TPM), and super-resolution microscopy.