Vectorial optical fields have recently attracted significant attention due to their importance in sensing, imaging, light-matter interactions and controlling photonic responses of nanoparticles and nanostructures. In this respect, the interaction of polarised fields with chiral nano-objects is of particular interest because controlling directionality of scattering via chirality of light or nanostructures would open up new applications in nanophotonics and photochemistry. Here, a novel concept of rotating chiral dipoles is introduced to obtain the relationship between the directionality and the handedness of scattering fields and realize unidirectional chiral scattering. Through the engineering of multipole excitation in plasmonic helicoid nanoparticles, we systematically introduce and demonstrate, both numerically and experimentally, the rotating chiral dipole for highly-directional forward scattering of circularly-polarized light. This concept of rotating chiral dipoles may be important for designing scattering from nanostructures and optical nano-antennas.
Optical vector field topologies will be discussed on the example of plasmonic systems and anisotropic metamaterials. An anisotropic metamaterial platform for local control of polarisation in complex vector beams, including radial and azimuthal beams, will be presented. The approach enables a flexible platform for tailoring complex vector beams and achieving required polarisation patterns on demand for harvesting functionalities and applications of complex light beams with complex polarisation and phase information in numerous photonic and quantum technologies, imaging and metrology.
Dielectric and plasmonic metasurfaces provide excellent control over the shaping of optical wavefronts via the manipulation of polarisation, phase and amplitude of the light. Taking advantage of their subwavelength thicknesses, metasurfaces are a very promising technology in a variety of applications including beam steering and focusing, polarisation and angular momentum control. Recently, holographic information encoding for 3D displays using metasurfaces has also been of interest, creating effective techniques for the 2D visualisation of 3D objects. Normal mapping, for example, is widely used in computer graphics to create shading effects and recreate 3D-like features of surface textures. Here, we report on the development of the concept of surface normal mapping for the representation of 3D objects and shading effects with optical metasurfaces. In this work, the metasurface is designed to implement diffuse reflection and uses the concept of normal mapping to control its scattering properties. As a proof of principle, a flat diffuse metasurface imitating lighting and shading effects of a 3D cube was characterised under incoherent illumination. The “3D image” is displayed directly on the illuminated metasurface and its shading varies in response to the change in illumination angle. The metasurface performs in a broad range of the visible spectrum, including the three RGB wavelengths. The 3D images created via normal mapping based on optical metasurfaces provide an effective technology for 3D security features and anti-counterfeiting. This type of metasurfaces can also be useful in the design of efficient optical diffusers for display technology and etalons for metrology.
Structured light finds many interesting applications in numerous fields, such as information encoding, wavefront manipulation and imaging. The opportunity to engineer the field distributions of optical beams opens up many exciting possibilities for achieving new optical interactions with materials and molecules. In this work we theoretically and experimentally investigate the interaction of cylindrical vortex beams (CVBs) with a strongly anisotropic plasmonic metamaterial, focusing on the case of radially and azimuthally polarised beams. We developed a semi-analytical model to describe the propagation of CVBs through an anisotropic slab, describing the metamaterial by means of an effective medium theory. In the tight focusing regime, the extinction properties of the metamaterial show the sample sensitivity to different symmetries of the electric field distributions, as well as the important role of the longitudinal field components of the beam on the extinction. Strong dichroism of the anisotropic metamaterial results in variations of the beam modal structure by differently influencing the three components of the field. Moreover, decomposing the beam intensity profiles in the Laguerre-Gauss mode basis reveals a non-negligible variation of the modal content of the beam, induced by the nanorod metamaterial anisotropy. Linear, radial and azimuthal polarisation states have been tested for metamaterials with different anisotropy parameters. Experimental results show a good agreement with the theoretical predictions, proving the promising potential of anisotropic metamaterials for manipulation of complex vector beams.
Controlled manipulation and trapping of submicron-size particles has many applications in different research fields, including those in the general areas of biology and soft-condensed matter physics. Optical tweezers that make use of strongly focused laser beams are widely used for this purpose. However, their trapping abilities are substantially limited by diffraction and a lack of scalability. To overcome this, nanostructures made of plasmonic materials have attracted significant attention, as their ability to concentrate energy to very small dimensions can be exploited to generate optical traps capable of acting on nanometer-size objects. Furthermore, and when compared to conventional systems, these plasmonic traps also provide large field enhancements that allow for lower input powers. Despite such advantages, these techniques still lack the ability to provide the controlled manipulation of the trapped objects over long distances.
In this work we present a Brownian ratchet, based on plasmonic interactions, which can optically trap and manipulate dielectric nanometer-sized beads over long distances. For this purpose, the geometries of the plasmonic ratchets and the respective electric fields were modelled with COMSOL Multiphysics, and the optical forces experienced by the beads were calculated with COMSOL Multiphysics and processed with MATLAB®. Additionally, we experimentally demonstrate the rectification of the random thermal motion of subwavelength dielectric beads into one specific direction by periodically turning on and off a laser beam that illuminates the plasmonic nanostructure array and exploiting the asymmetries in the system.
We develop an approach that enables characterization of wavelength-scale objects with deep subwavelength resolution. The technique combines diffractive imaging that out-couples the information about the subwavelength features of the object into the far-field zone with machine learning that analyzes the resulting patterns. Recovery of complex objects with 120-nm resolution with ~530-nm light is demonstrated experimentally. Our theoretical analysis suggests that the same objects can be recovered with up to 2-micron-wavelength light. Our work opens the door for new characterization tools that combine high spatial resolution, fast data acquisition, and artificial intelligence
KEYWORDS: Luminescence, Spectroscopy, Process control, Electromagnetism, Metamaterials, Composites, Biophysics, Quantum optics, Nanostructures, Resonance energy transfer
The control of photoluminescence processes, via the design of composite materials with engineered electromagnetic properties, is of great interest for the development of many application areas ranging from biophysics to quantum optical technologies. Approaches providing broadband enhancements of emission, not limited to resonant nanostructures, are particularly advantageous. We discuss how various photoluminescence processes, including conventional and dipolar-forbidden spontaneous emission, as well as Förster resonance energy transfer, are altered nearby and inside plasmonic hyperbolic metamaterials. They provide a flexible platform for engineering broadband Purcell enhancements due to their peculiar electromagnetic mode structure controlled by the nonlocal response of the metamaterial.
Dielectric and plasmonic metasurfaces provide excellent control over the shaping of optical wavefronts via the manipulation of polarisation, phase and amplitude of the light. Taking advantage of their subwavelength thicknesses, metasurfaces have shown to be a very promising technology in a variety of applications including beam steering and focusing, polarisation and angular momentum control, enhancement of nonlinear effects, as well as holographic information encoding for 3D displays. Recently, the emergence of virtual reality and augmented reality technologies have led to the constant demand of effective techniques for the 2D visualisation of 3D objects. Normal mapping, for example, is widely used in computer graphics to create shading effects and recreate 3D-like features of surface textures, such as regular patterns, bumps or ripples. Here, we report on the development of the concept of surface normal mapping for the representation of 3D objects and shading effects with optical metasurfaces. In this work, the metasurface is designed to implement diffuse reflection and uses the concept of normal mapping to control its scattering properties. As a proof of principle, a flat diffuse metasurface imitating lighting and shading effects of a 3D cube was fabricated and characterised under incoherent illumination. The “3D image” is displayed directly on the illuminated metasurface and its shading varies in response to the change in illumination angle. The metasurface performs in a broad range of the visible spectrum, including the three main RGB wavelengths. The 3D images created via normal mapping based on optical metasurfaces provide an effective technology for 3D security features and anti-counterfeiting. This type of metasurfaces can also be useful in the design of efficient optical diffusers for display technology and etalons for metrology.
The control of spontaneous emission via the design of composite materials with engineered electromagnetic properties is important for the development of new faster and brighter sources of illumination with applications ranging from biophysics to quantum optical technologies. In particular, the fabrication of nanostructures leading to broadband enhancement of emission is of great interest. Hyperbolic plasmonic metamaterials have recently emerged as a very flexible platform for this purpose as they provide a high local density of electromagnetic states available for the radiative relaxation of emitters. This is due to their peculiar mode structure governed by both the structural nonlocal response and the dispersion properties.
Here, we investigate the modification of the spontaneous emission rate and intensity enhancement of emitters located inside a nanorod-based hyperbolic metamaterial. We experimentally show the coupling of the radiated emission to the waveguided mode of a planar hyperbolic metamaterial with finite thickness. The emitters located inside this planar hyperbolic metamaterial waveguide exhibit an almost 50-fold reduction of the decay rate and 3-fold intensity enhancement of the fluorescence coupled to the mode. We also discuss the effect of nanostructuring the nanorod-based metamaterial on the spontaneous emission properties of emitters located inside it, where suitable designs can lead to further enhancement of the radiative rate and improved light extraction of the emission coupled to the high-wavevector modes of the metamaterial to the far-field, useful for the development of efficient and fast free-space light-emitting devices.
Fluorescence-based processes are strongly modified by the electromagnetic environment in which the emitters are placed. Hence, the design of nanostructured materials with appropriate electromagnetic properties opens up a new route in the control of, for instance, the spontaneous rate of emission or the energy transfer rate in donor-acceptor pairs. In particular, hyperbolic plasmonic metamaterials have emerged as a very flexible and powerful platform for these applications as they provide a high local density of electromagnetic states due to their peculiar mode structure which is governed by both the structural nonlocal response and the dispersion properties. Here, we will discuss an experimental and theoretical study of the influence of a hyperbolic metamaterial comprised of an array of gold nanorods on the radiative properties of quantum emitters and the energy-transfer processes between them.
KEYWORDS: Metamaterials, Plasmonics, Fluorescence resonance energy transfer, Electromagnetism, Resonance energy transfer, Luminescence, Energy transfer, Molecules, Molecular energy transfer, Biosensing
The control of the Förster resonance energy transfer (FRET) rate between molecules has recently received a lot of interest, opening opportunities in the development of sources of incoherent illumination, photovoltaics and biosensing applications. The design of nanostructured materials with appropriate electromagnetic properties, particularly with the engineered local density of electromagnetic states (LDOS), allows the enhancement of the spontaneous emission rate of emitters in their vicinity. However, the question of the influence of the LDOS on the energy transfer rate between emitters remains controversial. To date, several contradicting theoretical and experimental studies involving emitters on metallic surfaces and plasmonic metamaterials as well as in optical cavities and plasmonic antennas have been reported. In this work we study the influence of the LDOS on the energy transfer between donor-acceptor pairs placed inside the anisotropic metamaterial. The study of the emission kinetics of both the donor and the acceptor allow us to experimentally compare FRET efficiencies in different electromagnetic environments including dielectric and plasmonic substrates as well as metamaterials.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.