Flexible metamaterials at visible wavelengths

We report on the fabrication and characterization of plasmonic structures on flexible substrates (Metaflex) and demonstrate the optical properties of a single layer of Metaflex. The layer exhibits a plasmonic resonance in the visible region around 620 nm. We show experimental and numerical results for both nano-antennas and fishnet geometries. We anticipate the use of Metaflex as a building block for flexible metamaterials in the visible range.Publisher PDFPeer reviewe

The role of the plasmon resonance for enhanced optical forces

Optical manipulation of nanoscale objects is studied with particular emphasis on the role of plasmon resonance for enhancement of optical forces. The thesis provides an introduction to plasmon resonance and its role in confinement of light to a sub-diffraction volume. The strong light confinement and related enhancement of optical forces is then theoretically studied for a special case of nanoantenna supporting plasmon resonances. The calculation of optical forces, based on the Maxwell stress tensor approach, reveals relatively weak optical forces for incident powers that are used in typical realisations of trapping with nanoantenna. The optical forces are so weak that other non-optical effects should be considered to explain the observed trapping. These effects include heating induced convection, thermoporesis and chemical binding. The thesis also studies the optical effects of plasmon resonances for a fundamentally different application - size-based optical sorting of gold nanoparticles. Here, the plasmon resonances are not utilised for sub-diffraction light confinement but rather for their ability to increase the apparent cross-section of the particles for their respective resonant sizes. Exploiting these resonances, we realise sorting in a system of two counter-propagating evanescent waves, each at different wavelength that selectively guide gold nanoparticles of different sizes in opposite directions. The method is experimentally demonstrated for bidirectional sorting of gold nanoparticles of either 150 or 130 nm in diameter from those of 100 nm in diameter within a mixture. We conclude the thesis with a numerical study of the optimal beam-shape for optical sorting applications. The developed theoretical framework, based on the force optical eigenmode method, is able to find an illumination of the back-focal plane of the objective such that the force difference between nanoparticles of various sizes in the sample plane is maximised

Optical forces near a nanoantenna

Partially funded by UK EPSRCThe Maxwell stress tensor method is used to calculate the optical forces acting upon a glass nanosphere in the proximity of optically excited gold nanoantenna structures. The dependence of optical forces over a full range of excitation angles is explored: the total internal reflection excitation does not bring any particular advantage to trapping efficiency when compared to the normal incidence excitation. Our calculations show multiple trapping sites with similar trapping properties for the normal and the total internal reflection cases, respectively; furthermore, the convective heating probably dominates over any optical forces in such systems.PostprintPeer reviewe

Developing a needle-like optical funnel: Numerical modelling

Non-diffracting optical quasi-Bessel beams provide an opportunity to construct optical fields of complex architecture. The constructed beams may have a bright central peak or zero intensity on the beam axis and have the beam size of only a few microns propagating over a long-defined distance, which is not possible with conventional Gaussian or high-order Laguerre- Gaussian beams. In this work we demonstrate the possibility of constructing a needle-like diverging optical funnel with zero intensity on the axis. The primary aim is to numerically construct and optimize the optical field, which could transversely compress and focus a stream of μm- and sub-μm size particles injected into vacuum or gaseous environment by applying light pressure and photophoretic forces pushing particles into the area with lower intensity. We present the results of numerical modelling of an "optical funnel" based on re-imaging a non-zero-order quasi-Bessel beam, formed by an axicon and a phase plate or using an SLM, with a collimator. The funnel geometry, namely, the μm-size of the beam cross-section, several-mm long propagation length and its divergence, all is controlled and optimized by changing the topological charge at a fixed collimation of the re-imaging optics, or/and by varying the collimation with fixed topological charge of the beam. The simulated profiles will have an application for optical guiding and focusing of aerosolised beam of particles, large biomolecules and viruses to the micron-size focus of x-ray Free Electron Lasers in order to increase the delivery efficiency of isolated single particles in coherent diffractive imaging experiments

Willin as a novel 4.1 ezrin radixin moesin (FERM) domain protein in the mammalian hippo signalling pathway

Electronic version excludes material for which permission has not been granted by the rights holderThe Salvador/Warts/Hippo (Hippo) pathway defines a novel signalling cascade regulating cell contact inhibition, organ size control, cell growth, proliferation, apoptosis and cancer development in mammals. The Hippo pathway was initially utilised in D. melanogaster, where the Expanded protein acts in the Hippo signalling cascade to control organ size. Willin is the proposed human orthologue of Expanded and the aim of this thesis is to investigate whether willin can activate the mammalian Hippo signalling pathway. Ectopic willin expression causes an increase in phosphorylation of the core Hippo signalling pathway components MST1/2, LATS1 and YAP, an effect which can be antagonised by ezrin. In MCF10A cells, willin over-expression antagonises a YAP-induced epithelial-to-mesenchymal transition via the N- terminal FERM (Four-point-one Ezrin Radixin Moesin) domain of willin. Preliminary results show that willin is expressed within the sciatic nerve of rat and mice, and within the neuromast cells in the zebrafish; suggesting that willin and the Hippo pathway may play a vital role in the developmental regulation within the peripheral nervous system. To conclude, willin influences Hippo signalling activity by activating the core Hippo pathway kinase cassette in mammalian cells

Non-imaging Optics of multi-LED light source for hyperspectral imaging

The main objective of our work was to design a light source which should be capable to collect and illuminate light of LEDs at the smaller aperture of cone (9mm) which could be either coupled with secondary optics of a microscope or utilized independently for hyperspectral studies. Optimized performance of cone was assessed for different substrates (diffused glass silica, Alumina, Zerodur glass, acrylic plastic) and coating surfaces (white diffused, flat white paint, standard mirror) using a simulation software. The parameters optimized for truncated cone include slanting length and Top Major R (Larger diameter of cone) which were also varied from 10 to 350 mm and 10 to 80 mm respectively. In order to see affect of LED positions on cone efficiency, the positions of LED were varied from central axis to off-axis. Similarly, interLED distance was varied from 2 mm to 6 mm to reckon its effect on the performance of cone. The optimized Slant length (80 mm) and Top Major R (50 mm) were determined for substrates (glass zerodur or acrylic plastic) and coating surface (standard mirror). The output profile of truncated source was found non uniform, which is a typical presentation of non imaging optics problem. The maximum efficiency of cone has been found for LED at the centre and it was found decreasing as LED moves away from the central axis. Moreover, shorter the interLED distance, better is the performance of cone. The primary optics of cone shaped light source is capable to lit visible and UV LEDs in practical design. The optimum parameters obtained through simulations could be implemented in the fabrication procedure if the reflectance of source would have been maintained upto finish level of a standard mirror.1 page(s

Determination of optical forces in the proximity of a nanoantenna

We have used the Maxwell stress tensor method to calculate the optical forces acting upon a dielectric nanosphere in the proximity of gold nanoantenna structure optically excited by a plane wave. We have explored the dependence of optical forces for the full range of excitation angles with the conclusion that the maximum force occurs for the excitation at critical angle. The large force at this angle is, however, at the expense of greatly increased intensity in the volume of the particle from which we conclude that the important measure for the trapping efficiency in the case of plasmonic nanostructures is not the incident intensity of the plane wave, but rather the local intensity averaged over the volume of the particle. Our calculations further show multiple trapping sites with similar trapping properties, which leads to uncertainty in the trapping position. Furthermore, our calculations show that the heating effects might play a significant role in the experimentally observed trapping.9 page(s