Marios Sergides

Selective particle trapping and optical binding in the evanescent field of an optical nanofiber.

The evanescent field of an optical nanofiber presents a versatile interface for the manipulation of micron-scale particles in dispersion. Here, we present a detailed study of the optical binding interactions of a pair of 3.13 μm SiO(2) spheres in the nanofiber evanescent field. Preferred equilibrium positions for the spheres as a function of nanofiber diameter and sphere size are discussed. We demonstrated optical propulsion and self-arrangement of chains of one to seven 3.13 μm SiO(2) particles; this effect is associated with optical binding via simulated trends of multiple scattering effects. Incorporating an optical nanofiber into an optical tweezers setup facilitated the individual and collective introduction of selected particles to the nanofiber evanescent field for experiments. Computational simulations provide insight into the dynamics behind the observed behavior.

Higher order microfibre modes for dielectric particle trapping and propulsion.

Optical manipulation in the vicinity of optical micro- and nanofibres has shown potential across several fields in recent years, including microparticle control, and cold atom probing and trapping. To date, most work has focussed on the propagation of the fundamental mode through the fibre. However, along the maximum mode intensity axis, higher order modes have a longer evanescent field extension and larger field amplitude at the fibre waist compared to the fundamental mode, opening up new possibilities for optical manipulation and particle trapping. We demonstrate a microfibre/optical tweezers compact system for trapping and propelling dielectric particles based on the excitation of the first group of higher order modes at the fibre waist. Speed enhancement of polystyrene particle propulsion was observed for the higher order modes compared to the fundamental mode for particles ranging from 1 μm to 5 μm in diameter. The optical propelling velocity of a single, 3 μm polystyrene particle was found to be 8 times faster under the higher order mode than the fundamental mode field for a waist power of 25 mW. Experimental data are supported by theoretical calculations. This work can be extended to trapping and manipulation of laser-cooled atoms with potential for quantum networks.

Plasmonic nanoring devices for micro- and nanoparticle trapping and detection using low incident laser powers

Trapping and detection of micro- and nano-objects at low incident laser powers in the near-infrared region (NIR) is crucial for many biological applications. Using a conventional optical tweezer method, trapping is limited to dielectric particles larger than 100nm in size with high incident laser powers. For this reason, plasmonic nanostructures, which have recently attracted research attentions, offered enhanced trapping fields at their resonant wavelengths, and subsequently can be used to trap and detect silica dielectric particles down to 12nm and single 3.4nm bovine serum albumin proteins using low incident powers (<; 1mW). In this work, we propose a design consisting of nanodisk and nanohole arrays on a 50 nm gold thin film. We demonstrate that this tunable nano-plasmonic device toward the NIR range can improve both the trapping field enhancement and detection of nano-objects using the singular phase drop methods. The tunability of the device was investigated from extinction and reflection spectra while increasing the aperture size in the arrays. The ellipsometric parameters were used to study the dark topologically-protected position, where a rapid change in phase can occur. Our experimental data suggests that, using this abrupt phase change, one can improve the detection sensitivity 10 times compared to the conventional extinction spectra method. In order to investigate the capability of trapping submicron particles with low incident laser powers, we integrated the nano-plasmonic device into a standard optical tweezer system. Stable trapping, with the capability of two-dimensional manipulation of 500 nm fluorescent polystyrene particles over large ranges for seveal minutes, was demonstrated using low incident laser powers of less than 500 μW at 950 nm. The optical trap stiffness and trapping efficiencies of these nanostructured plasmonics devices were experimentally analyzed. The experimental observation shows that stronger optical submicron particle traps can be achieved with approximately 20 times lower incident power when compared to the conventional optical tweezer method.

Particle propulsion using higher order microfiber modes

Propulsion of polystyrene particles in the evanescent field of the first group of higher order modes in an optical microfiber were studied. Higher speeds were observed for higher order mode propulsion than for fundamental mode.

Characterization of periodic plasmonic nanoring devices for nanomanipulation

We study the optical properties of hybrid gold nanodisk and nanohole arrays and present experimental evidence of nanoparticle trapping using these devices. The fabrication procedure using electron beam lithography (EBL) is also discussed. This hybrid design exhibits a splitting of the resonance modes (low and high energy modes) due to the coupling of the electromagnetic interaction between nanohole and nanodisk plasmons. The devices demonstrate high plasmon resonance tunabilities from the visible to the near-infrared region (NIR) by varying the dimensions of the features of this design. This enhancement in the NIR is highly desirable for the purposes of biological sample manipulation where photo damage should be low. Additionally, these devices consist of grooves connecting the hybrid structures to each other. These regions provide further enhancement of the local electric fields and play the role of the trapping sites. We demonstrate multiple dielectric nanoparticle trapping in these grooves while the devices are excited by evanescent fields via the Kretschmann configuration. The results provide good evidence of the potential of this design to be used for the manipulation of biological samples with sub-diffraction limit sizes.

Towards polarization-sensitive trapping of nanoparticles in nanoring apertures

Double nanohole apertures in metal films have proven to be efficient plasmonic devices for trapping nanoparticles as small as single proteins.1 To date, this technique has relied on weak transmission far beyond the wavelength cutoff, ignoring the prospect of plasmon field enhancement. In this work we present details on the design and fabrication of arrays of nanoring apertures on gold films. These devices feature efficient light localization in small gaps similar to double nanohole apertures, but additionally benefit from surface plasmon resonances in the near infrared spectrum. We perform polarization-resolved spectrometry on the arrays and discuss their potential for nanoparticle trapping.