Modulating the trapping and manipulation of semiconductor particles using Bessel beam optical tweezers

We show that the optical trapping and manipulation of spherical-shaped semiconductor (germanium) particles can be strongly modulated and controlled using optical tweezers based on a highly focused Bessel beam. Depending on the setup parameters, the germanium beads can be stably trapped outside the optical axis, present a characteristic oscillatory dynamics near the focal plane or even be repelled from the focus. This intricate behavior was studied by varying relevant parameters such as the laser power, the radius of the Bessel beam and the focal height of the trap. The results show that Bessel beam optical tweezers using germanium beads are very versatile tools for applying pico- to femto-Newton constant or oscillatory forces on systems, opening perspectives for new applications in soft matter science and correlated fields, as well as in the construction of microdevices.