Dynamics of Pulsed-Laser Interaction with Janus Particles.

Janus particles, with their flexible chemistry and multifunctionality, have broadened the scope of the optical manipulation field as an emerging class of materials. Laser-based manipulation is particularly promising for half-metal-coated particles, offering a platform to study optical and thermal effects. However, the role of the laser's operation regime in particle behavior needs to be understood better. Hence, in this work, we studied the interaction of nanosecond-pulsed lasers on 4.1 μm Au-Janus particles with a 100 nm gold cap. We focused on the interaction in three sections: (1) We observed three pulse energy influence regimes: In the low-influence regime (less than ∼10 nJ), the particle maintains its intrinsic Brownian motion. In the medium-influence regime (less than ∼40 nJ), the particle exhibits an extended range of motion. In the high-influence regime (higher than ∼40 nJ), the particle undergoes superdiffusion and establishes a new equilibrium position. (2) During optical manipulation trials, a threshold pulse energy of 4 nJ (average power of 40 μW) was sufficient to move Au-Janus particles against the laser spot. We achieved translation velocities of 0.9-5.1 μm/s at 4-50 nJ. (3) The gold cap is damaged at 20 nJ (fluence of 0.7 J/cm) when the laser is focused on the particle, consistent with theoretical predictions, and the ablation process generates micro- and submicrometer gold particles. These findings reveal the potential of pulsed lasers for precise, power-efficient manipulation of Janus particles, advancing our understanding of laser-particle interactions and opening new pathways for optical manipulation applications.