Boris Luk'yanchuk

The Fano resonance in plasmonic nanostructures and metamaterials

Since its discovery, the asymmetric Fano resonance has been a characteristic feature of interacting quantum systems. The shape of this resonance is distinctively different from that of conventional symmetric resonance curves. Recently, the Fano resonance has been found in plasmonic nanoparticles, photonic crystals, and electromagnetic metamaterials. The steep dispersion of the Fano resonance profile promises applications in sensors, lasing, switching, and nonlinear and slow-light devices.

Optical virtual imaging at 50 nm lateral resolution with a white-light nanoscope

The imaging resolution of a conventional optical microscope is limited by diffraction to ~200 nm in the visible spectrum. Efforts to overcome such limits have stimulated the development of optical nanoscopes using metamaterial superlenses, nanoscale solid immersion lenses and molecular fluorescence microscopy. These techniques either require an illuminating laser beam to resolve to 70 nm in the visible spectrum or have limited imaging resolution above 100 nm for a white-light source. Here we report a new 50-nm-resolution nanoscope that uses optically transparent microspheres (for example, SiO₂, with 2 μm<diameter<9 μm) as far-field superlenses (FSL) to overcome the white-light diffraction limit. The microsphere nanoscope operates in both transmission and reflection modes, and generates magnified virtual images with a magnification up to ×8. It may provide new opportunities to image viruses and biomolecules in real time.1 Laser Processing Research Centre, School of Mechanical, Aerospace, and Civil Engineering, University of Manchester, Manchester M60 1QD, UK 2 Corrosion and Protection Centre, School of Materials, University of Manchester, The Mill, University of Manchester, Manchester M60 1QD, UK 3 Data Storage Institute, DSI Building, 5 Engineering Drive 1, Singapore, 117608 Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576 *E-mail: zengbo.wang@manchester.ac.uk

Strategy of nanocluster and nanostructure synthesis by conventional pulsed laser ablation

We describe the basic principles of nanoparticle synthesis by conventional pulsed laser ablation. The generalization of the Zeldovich and Raizer theory of condensation has been performed for inhomogeneous laser-induced plume where the rates of nucleation as well as the condensation times are different for different parts of the plume. The theoretical development and analysis of the experimental results are given for condensation, expansion and properties of silicon nanoclusters.

An analytical model for three-dimensional laser plume expansion into vacuum in hydrodynamic regime

Abstract Dynamic of a dense, laser-produced vapor plume is studied. The analysis is based on the special solution of gas dynamics equations that describes the expansion of an ellipsoidal gas cloud into vacuum. This solution is employed to explain the apparent ‘rotation’ of the cloud — the so called ‘flip-over effect’. The flux of atoms onto the substrate and the film thickness profile are calculated using the model. The present model can be used for the interpretation of the time-of-flight spectra of atoms in laser ablation, and for the description of the shape of vapor cloud expanding into an ambient gas.

The influences of particle number on hot spots in strongly coupled metal nanoparticles chain.

In understanding of the hot spot phenomenon in single-molecule surface enhanced Raman scattering (SM-SERS), the electromagnetic field within the gaps of dimers (i.e., two particle systems) has attracted much interest as it provides significant field amplification over single isolated nanoparticles. In addition to the existing understanding of the dimer systems, we show in this paper that field enhancement within the gaps of a particle chain could maximize at a particle number N>2, due to the near-field coupled plasmon resonance of the chain. This particle number effect was theoretically observed for the gold (Au) nanoparticles chain but not for the silver (Ag) chain. We attribute the reason to the different behaviors of the dissipative damping of gold and silver in the visible wavelength range. The reported effect can be utilized to design effective gold substrate for SM-SERS applications.

Laser-induced cavitation bubbles for cleaning of solid surfaces

When a high-power laser beam is focused into liquid, it results in a shock wave emission and cavitation bubble generation. Upon inserting a rigid substrate into the liquid, the bubbles migrate towards the substrate due to the Bjerknes attractive force. Due to bubble–substrate and/or bubble–free-surface interaction, a high-speed liquid jet is formed during bubble collapse, and a collapse shock wave is generated at the moment of bubble collapse near the substrate. These shock waves and liquid jet induce large forces acting on the substrate to remove particles from it. For a substrate several millimeters away from the laser focus point, the collapse shock wave and liquid jet play key roles in removal of particles. The cleaning efficiency increases with an increase of laser fluence and decreases with an increase of distance between substrate surface and laser beam focus point or depth below liquid surface. In a case of bubbles close to substrate and liquid-surface boundaries, implosion of the bubbles will giv...

Generalized Brewster effect in dielectric metasurfaces.

Polarization is a key property defining the state of light. It was discovered by Brewster, while studying light reflected from materials at different angles. This led to the first polarizers, based on Brewsters effect. Now, one of the trends in photonics is the study of miniaturized devices exhibiting similar, or improved, functionalities compared with bulk optical elements. In this work, it is theoretically predicted that a properly designed all-dielectric metasurface exhibits a generalized Brewsters effect potentially for any angle, wavelength and polarization of choice. The effect is experimentally demonstrated for an array of silicon nanodisks at visible wavelengths. The underlying physics is related to the suppressed scattering at certain angles due to the interference between the electric and magnetic dipole resonances excited in the nanoparticles. These findings open doors for Brewster phenomenon to new applications in photonics, which are not bonded to a specific polarization or angle of incidence.

Hybrid phase-change plasmonic crystals for active tuning of lattice resonances.

Tunable lattice resonances are demonstrated in a hybrid plasmonic crystal incorporating the phase-change material Ge2Sb2Te5 (GST) as a 20-nm-thick layer sandwiched between a gold nanodisk array and a quartz substrate. Non-volatile tuning of lattice resonances over a range Δλ of about 500 nm (1.89 µm to 2.27 µm) is achieved experimentally via intermediate phase states of the GST layer. This work demonstrates the efficacy and ease of resonance tuning via GST in the near infrared, suggesting the possibility to design broadband non-volatile tunable devices for optical modulation, switching, sensing and nonlinear optical devices.

Angle effect in laser nanopatterning with particle-mask

Parallel nanostructuring of substrate surface with particle-mask is a promising technology that may significantly improve the patterning speed under single laser pulse irradiation. In this paper, the influence of the incidence wave angle on the pattern structures is investigated. Polystyrene spherical particles were deposited on the surface in a monolayer form by self-assembly. The sample was then irradiated with 248nm KrF laser at different incidence angles α. It is found that nanostructures can be formed at different positions with different incidence angles. Both round-shape and comet-shape nanostructures can be produced. By varying the incidence angles, the depth of the nanostructures can also be controlled. To explain the different nanostructures produced at different angles, the intensity field distributions under the particle were calculated according to an exact model for light scattering by a sphere on the substrate (P. A. Bobbert and J. Vlieger, Physica A 137A, 209 1986). The main equation in th...

Laser micro/nano fabrication in glass with tunable-focus particle lens array

Based on medium-tuned optical field enhancement effect around a self-assembled particle-lens array (PLA) irradiated with a femtosecond (fs) laser source, we demonstrated that high-precision periodical array of micro/nano-structures can be readily fabricated on glass surface or inside glass in large areas in parallel without any cracks or debris. The technique has potential for rapid fabrication of three-dimensional structures in multiple layers inside glass.