The demonstration of enhanced spontaneous emission of nanoscaled optical emitters near metallic nanoparticles and the recent realization of a nanolaser based on surface plasmon amplification by stimulated emission of radiation (spaser) encourage the search for strong coupling regime at the nanoscale. Here we propose the concept of nanopolaritons. We demonstrate with accurate scattering calculations that the strong coupling regime of a single quantum emitter (a semiconductor quantum dot) placed in the gap between two metallic nanoparticles can be achieved. The largest dimension of the investigated system is only 36 nm. Nanopolaritons will advance our fundamental understanding of surface plasmon enhanced optical interactions and could be used as ultra-compact elements in quantum-information technology.

We study the Brownian motion (BM) of optically trapped graphene flakes. These orient orthogonal to the light polarization, due to the optical constants anisotropy. We explain the flake dynamics, measure force and torque constants and derive a full electromagnetic theory of optical trapping. The understanding of two dimensional BM paves the way to light-controlled manipulation and all-optical sorting of biological membranes and anisotropic macromolecules.The random motion of microscopic particles in a fluid was first observed in the late eighteenth century, and goes by the name of Brownian motion(BM) [1]. This was ascribed to thermal agitation[2], leading to Einstein's predictions of the resulting particle displacements [3]. BM is ubiquitous throughout physics, chemistry, biology, and even finance. It can be harnessed to produce directed motion [4]. It was also suggested that thermally activated BM may be responsible for the movement of molecular motors, such as myosin and kinesin [5]. When a Brownian particle (BP), i.e. a particle undergoing BM, is subject to an external field, e.g. a confining potential, the fluid damps the BM and, in a high damping regime, such as for a BP in water, the confining potential acts as a cut-off to the BM dynamics. This is free for short times (high frequency limit), while is frozen at longer times (low frequency limit) [8]. These processes have perfect ground in experiments with optical traps, where a BP is held by a focused laser beam, i.e. an optical tweezers [9]. In this context, BM can be utilized to investigate the properties of the surrounding environment [10,11], as well as of the trapped particle, and for accurate calibration of the spring constants of the optical harmonic potential [12,13].Dimensionality plays a special role in nature. From phase transitions [14], to transport phenomena[15], twodimensional (2d) systems often exhibit a strikingly different behavior [14]. Nanomaterials are an attractive target for optical trapping [16][17][18]. This can lead to top-down organization of composite nano-assemblies[16], sub-wavelength imaging by the excitation and scanning of nano-optical probes [17], photonic force microscopy with increased space and force resolution [18]. Graphene[19] is the prototype 2d material, and, as such, has unique mechanical, thermal, electronic and optical properties [20]. Here, we use graphene as prototype material to unravel the consequences of BM in 2d.Graphene is dispersed by processing graphite in a water-surfactant solution, Fig.1a. We do not use any functionalization nor oxidation, to retain the pristine electronic structure in the exfoliated monolayers [21][22][23]. We use di-hydroxy sodium deoxycholate surfactant. High resolution Transmission Electron Microscopy (HRTEM) shows∼10-40nm flakes. Fig.1b is an image of one such flake, with the typical honeycomb lattice. By analyzing over a hundred flakes, we find∼ 60% single-layer (SLG), much higher than previous aqueous [22] and nonaqueous dispersions [21], and the remainder bi-and trilayers (Fi...

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We study the optical trapping of highly elongated linear nanostructures in the focal region of a high-numerical aperture lens (optical tweezers). The radiation torque and trapping force on these nanostructures that are modeled as chains of identical spherical scatterers are calculated by means of multipole field expansions in the framework of the transition matrix approach. We investigate both orientational and trapping stability and calculate force constants and trap parameters in order to clarify the role of the linear geometry in the optical trapping mechanism. Furthermore, we calculate optical trapping of nanowires of different materials and compare our theoretical findings with available experimental results.

We investigate size-scaling in optical trapping of ultrathin silicon nanowires showing how length regulates their Brownian dynamics, optical forces, and torques. Force and torque constants are measured on nanowires of different lengths through correlation function analysis of their tracking signals. Results are compared with a full electromagnetic theory of optical trapping developed in the transition matrix framework, finding good agreement.