Miniaturized holographic twin trap 3D-printed via two-photon lithography

We introduce the concept and realization of a miniaturized holographic twin trap for optical trapping of microparticles. The hybrid refractive–diffractive microlens, manufactured on a glass slide by two-photon lithography, generates two axially separated foci, which are superposed by a mirror to obtain a counterpropagating trap. We present the optical design and an optimization strategy to balance the intensities of the zeroth- and first-order foci of the manufactured microlenses. Furthermore, we apply our approach experimentally and demonstrate stable trapping of 3 μm polystyrene beads in water.