Temperature mediated 'photonic hook' nanoparticle manipulator with pulsed illumination.

Optical forces applied on an object or cell in a non-destructive manner have revolutionised scientific instruments. Optical tweezers and atomic traps are just two representative examples. Curved forces such as photonic hooks are of particular interest for non-destructive manipulation; however, they are extremely weak in low-contrast media. Here, for the first time, we report the amplification of optical forces generated by a photonic hook via pulsed illumination mediated by temperature effects. We show that the optical force generated by the photonic hook subjected to illumination by an incident Gaussian pulse is significantly larger than the optical force generated by the photonic hook subjected to a continuous wave. We notice that under the applied photonic hook generated by a Gaussian beam, a spherical gold nanoparticle experiences a variation in its lattice temperature of Δ T l ∼ 2-4 K, leading to high index resolution. We envision that heat-associated effects can be further mitigated to achieve temperature assisted photonic hook manipulation of nanoparticles in a controllable manner by taking into account the thermo-optical properties of metals. Our findings are particularly important for tracing objects in low-contrast environments, such as optomechanically controlled drug delivery with nanoparticles in intercellular and intracellular media or cellular differentiation, to list a few examples.