No abstract

Optical manipulation of nanoparticles (NPs) with nanoscale precision has been a goal of several research fields. One of the promising ways to realize this is the usage of localized surface plasmon (LSP). The electric field at hotspots near metallic structures is highly localized, which generates a sufficient force to trap NPs, and at the same time, the optical nonlinearity of NPs appears. In this Letter, we propose a scheme to superresolutionally trap the NP into a particular hotspot of the metallic nanostructure array. The scheme is based on the optical nonlinearity of NPs, and utilizes two kinds of structured light: Gaussian and Laguerre-Gaussian beams. The results show the significant role of the optical nonlinearity in LSP trappings, and they are expected to open up new degrees of freedom to manipulate NPs.

Theoretical formalism for DC-field polaron dynamics is extended to the dynamics of a 1D Holstein polaron in an external AC electric field using multiple Davydov trial states. Effects of carrier-phonon coupling on detuned and resonant scenarios are investigated for both phase and nonzero phase. For slightly off-resonant or detuned cases, a beat between the usual Bloch oscillations and an AC driving force results in super Bloch oscillations, that is, rescaled Bloch oscillations in both the spatial and the temporal dimension. Super Bloch oscillations are damped by carrier-phonon coupling. For resonant cases, if the carrier is created on two nearest-neighboring sites, the carrier wave packet spreads with small-amplitude oscillations. Adding carrier-phonon coupling localizes the carrier wave packet. If an initial broad Gaussian wave packet is adopted, the centroid of the carrier wave packet moves with a certain velocity and with its shape unchanged. Adding carrier-phonon coupling broadens the carrier wave packet and slows down the carrier movement. Our findings may help provide guiding principles on how to manipulate the dynamics of the super Bloch oscillations of carriers in semiconductor superlattice and optical lattices by modifying DC and AC field strengths, AC phases, and detuning parameters.

Light has momentum, and hence, it can move small particles. The optical tweezer, invented by Ashkin et al. [Opt. Lett. 11, 288 (1986)] is a representative application. It traps and manipulates microparticles and has led to great successes in the biosciences. Currently, optical manipulation of “nano-objects” is attracting growing attention, and new techniques have been proposed and realized. For flexible manipulation, push–pull switching [Phys. Rev. Lett. 109, 087402 (2012)] and super-resolution trapping by using the electronic resonance of nano-objects have been proposed [ACS Photonics 5, 318 (2017)]. However, regarding the “rotational operation” of nano-objects, the full potential of optical manipulation remains unknown. This study proposes mechanisms to realize rotation and direction switching of nano-objects in macroscopic and nanoscopic areas. By controlling the balance between the dissipative force and the gradient force by using optical nonlinearity, the direction of the macroscopic rotational motion of nano-objects is switched. Further, conversion between the spin angular momentum and orbital angular momentum by light scattering through localized surface plasmon resonance in metallic nano-complexes induces optical force for rotational motion in the nanoscale area. This study pieces out fundamental operations of the nanoscale optical manipulation of nanoparticles.