An Optically Controlled Microscale Elevator Using Plasmonic Janus Particles

Spas Nedev, Sol Carretero-Palacios, Paul Kühler, Theobald Loehmuller, Alexander S. Urban, Lindsey JE Anderson, and Jochen Feldmann

In this article, we report how Janus particles, comprised of a silica sphere with a gold half shell, can not only be stably trapped by optical tweezers, but also displaced controllably along the axis of the laser beam through a complex interplay between optical and thermal forces. Scattering forces orient the asymmetric particle, while strong absorption on the metal side induces a thermal gradient, resulting in particle motion. An increase in the laser power leads to an upwards motion of the particle, while a decrease leads to a downwards motion. We study this reversible axial displacement, including a hysteretic jump in the particle position that is a result of the complex pattern of a tightly focused laser beam structure above the focal plane. As a first application we simultaneously trap a spherical gold nanoparticle and show that we can control this distance between the two particles inside the trap. This photonic micron-scale “elevator” is a promising tool for thermal force studies, remote sensing as well as optical and thermal micromanipulation experiments.

DOI