Switchable optical trapping based on Mie-resonant phase-change nanoparticles

Optical tweezers have revolutionized the manipulation of nanoscale objects, offering versatile control over trapped particles. Typically, the manipulation and trapping capabilities of optical tweezers rely on adjusting either the trapping laser beams or the optical environment surrounding the trapped nanoparticles. In our study, we present a novel approach to achieve tunable and switchable trapping using optical tweezers. We utilize nanoparticles made of a phase-change material (vanadium dioxide or VO₂), trapped by a focused Gaussian beam. By varying the intensity of the trapping beam, we can optically control the phase and optomechanical properties of the vanadium dioxide nanoparticles. At lower intensities, the nanoparticle remains in its monoclinic phase, and it is trapped by attractive optical forces. However, at higher intensities, the optical beam induces a phase transition in the nanoparticle to the rutile phase, which dramatically alters the optical forces, transforming them from attractive to repulsive, thereby pushing the nanoparticle away from the beam. Importantly, this effect is reversible, allowing the same particle to be attracted and repelled repeatedly. The observed phenomenon is governed by Mie resonances supported by the nanoparticle and their alterations during the phase transition of the VO₂ material. Our findings introduce a versatile new addition to the optical tweezers toolbox for optomechanical manipulation of nanoparticles.