Dynamics of self-thermophoretic Janus particle in optical trap

Optical manipulation of metallic Janus particles via self-thermophoresis results in complex trajectories due to competing effect of space-dependent speed and optical torque with the optical trapping presumed to have less or no effect. Here we report that when the beam size is comparable to the size of the particle and the laser power is small, optical trapping becomes relevant leading to the trajectory having a trochoidal-like behavior and off-center trapping. Brownian dynamics simulation incorporating space-dependent speed proportional to the local laser intensity, the induced optical torque, and optical trapping effect captures well the experimental data.