Showing papers by "David L. Andrews published in 2021"

500-Fold Amplification of Small Molecule Circularly Polarised Luminescence through Circularly Polarised FRET

Abstract: Strongly dissymmetric circularly polarised (CP) luminescence from small organic molecules could transform a range of technologies, such as display devices. However, highly dissymmetric emission is usually not possible with small organic molecules, which typically give dissymmetric factors of photoluminescence (gPL ) less than 10-2 . Here we describe an almost 103 -fold chiroptical amplification of a π-extended superhelicene when embedded in an achiral conjugated polymer matrix. This combination increases the |gPL | of the superhelicene from approximately 3×10-4 in solution to 0.15 in a blend film in the solid-state. We propose that the amplification arises not simply through a chiral environment effect, but instead due to electrodynamic coupling between the electric and magnetic transition dipoles of the polymer donor and superhelicene acceptor, and subsequent CP Forster resonance energy transfer. We show that this amplification effect holds across several achiral polymer hosts and thus represents a simple and versatile approach to enhance the g-factors of small organic molecules.

Orbital angular momentum of twisted light: chirality and optical activity

Abstract: Optical activity is conventionally understood as a natural difference in the optical responses of chiral materials with opposite handedness. It stems from the quantised spin angular momentum ±ħ per photon, with the ± representing either left- or right-handed circular polarisations. Less well known, until recently, was the possibility that matter might also respond in a similar, discriminatory way to the handedness of twisted light, or ‘optical vortices’, whose orbital angular momentum (OAM) is quantised as ℓℏ per photon, where ℓ is the topological charge whose sign determines a wavefront twist to the left or right. Initial studies focusing on whether, in spectroscopic applications, chiral matter might respond differently to the vortex handedness of +ℓ and −ℓ beams, failed to identify any viable mechanism. However, in the last few years, theory and experiment have both supplied ample evidence that, under certain conditions, such forms of interaction do exist—and as a result, the field of chirality and optical OAM is beginning to flourish at a pace. This topical review presents a survey of this new field, working up from a description of those initial studies to the cutting-edge experiments now taking place. Analysing the fundamental mechanisms provides for a revision of previous precepts, broadening their scope in the light of recent advances in understanding, and highlighting a vibrant synergy between the fields of optical activity and twisted light.

Optical activity in third-harmonic Rayleigh scattering: A new route for measuring chirality

Abstract: In 3D isotropic liquids, optical third-harmonic generation is forbidden, with circularly polarized light (CPL). Yet the associated nonlinear susceptibility directly influences the optical properties at the fundamental frequency by intensity dependence (Kerr effect). Here, the hidden third-harmonic optical properties upon CPL illumination are revealed by demonstrating a new effect, in hyper-Rayleigh scattering. This effect is succinctly enunciated: the intensity of light scattered at the third-harmonic frequency of the CPL incident light depends on the chirality of the scatterers. It is referred to as third-harmonic (hyper) Rayleigh scattering optical activity (THRS OA) and was observed from Ag nanohelices randomly dispersed in water. The first analytical theory model for the new effect in nanohelices is also provided, highlighting the role of localized transition dipoles along the helical length. THRS OA is remarkably user-friendly. It offers access to intricate optical properties (hyperpolarizabilities) that have so far been more easily accessible by computation and that are essential for the understanding of light−matter interactions. The new effect could find applications in hyper-sensitive characterization of the chirality in molecules and in nanostructures; this chirality plays a fundamental role in the function of bio/nano-machinery, with promising applications in next generation technologies.

Symmetry and Quantum Features in Optical Vortices

Abstract: Optical vortices are beams of laser light with screw symmetry in their wavefront. With a corresponding azimuthal dependence in optical phase, they convey orbital angular momentum, and their methods of production and applications have become one of the most rapidly accelerating areas in optical physics and technology. It has been established that the quantum nature of electromagnetic radiation extends to properties conveyed by each individual photon in such beams. It is therefore of interest to identify and characterize the symmetry aspects of the quantized fields of vortex radiation that relate to the beam and become manifest in its interactions with matter. Chirality is a prominent example of one such aspect; many other facets also invite attention. Fundamental CPT symmetry is satisfied throughout the field of optics, and it plays significantly into manifestations of chirality where spatial parity is broken; duality symmetry between electric and magnetic fields is also involved in the detailed representation. From more specific considerations of spatial inversion, amongst which it emerges that the topological charge has the character of a pseudoscalar, other elements of spatial symmetry, beyond simple parity inversion, prove to repay additional scrutiny. A photon-based perspective on these features enables regard to be given to the salient quantum operators, paying heed to quantum uncertainty limits of observables. The analysis supports a persistence in features of significance for the material interactions of vortex beams, which may indicate further scope for suitably tailored experimental design.

A Customizable Domain-Specific Memory-Centric FPGA Overlay for Machine Learning Applications

Abstract: This paper presents an overview and performance analysis of a software-programmable domain-customizable System-on-Chip (SoC) overlay for low-latency inferencing of variable and low-precision Machine Learning (ML) networks targeting Internet-of-Things (IoT) edge devices. The SoC includes a 2-D processor array that can be customized at design time for FPGA logic families. The overlay resolves historic issues of poor designer productivity associated with traditional Field Programmable Gate Array (FPGA) design flows without the performance losses normally incurred by overlays. A standard Instruction Set Architecture (ISA) allows different ML networks to be quickly compiled and run on the overlay without the need to resynthesize. Performance results are presented that show the overlay achieves $1.3\times-8.0\times$ speedup over custom designs while still allowing rapid changes to ML algorithms on the FPGA through standard compilation.

Discrete dipole approximation simulation of optical vortex excited plasmonic properties of a partially capped core-shell nanostructure

Abstract: In this study, interactions between optical vortex light and partially capped core-shell (PCCS) nanostructures simulated by a discrete dipole approximation (DDA) method are described. The plasmonic characteristics of the PCCS structure, in which a part of the surface of dielectric nanoparticles is covered with a metal cap, can be tuned by the core-shell ratio and the coverage condition. It was found that the topological charge and the polarization degree indicating the state of the optical vortex determine the resonance order, peak wavelength, direction and magnitude of optical torque of the excited pseudo-plasmon resonance of PCCS structures. It was also found that under certain incident conditions, higher-order resonance modes, such as hexapole and octupole modes are excited. Likewise, distorted resonance modes due to the asymmetry of the structure are excited. These plasmonic characteristics cannot be realized by scalar beam excitation, it becomes possible by an asymmetrical PCCS structure with optical vortex excitation.

A tribute to Marat Soskin

Abstract: Michael V Berry, S Soskin, E Brasselet, I Freund, Boris A Malomed, Valerii P Aksenov, C Rosales Guzmán, C N Alexeyev, A N Alexeyev, M A Yavorsky, L Tryfonyuk, A Ushenko, D L Andrews, L Torner, A Desyatnikov, Y Miyamoto, O Angelsky, P Banzer, Nikolay N Rosanov, F S Roux, V Venediktov, R O Vlokh, A Volyar, Y Egorov, A Rubass, G Gbur, M A Alonso, E Karimi and Mark R Dennis 1 H H Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL, United Kingdom 2 Department of Theoretical Physics, Institute of Semiconductor Physics, Kyiv, Ukraine 3 University of Bordeaux, CNRS, Laboratoire Ondes et Matière d’Aquitaine, F-33400 Talence, France 4 Physics Department, Bar Ilan University, Ramat Gan, Israel 5 Department of Physical Electronics, School of Electrical Engineering, and the Center for Light-Matter Interaction, Tel Aviv University, Tel Aviv, Israel 6 V.E. Zuev Institute of Atmospheric Optics SB RAS (IAO SB RAS), Tomsk, Russia 7 Wang Da-Heng Collaborative Innovation Center for Quantum Manipulation and Control, Harbin University of Science and Technology, Harbin 150080, People’s Republic of China 8 V. I. Vernadsky Crimean Federal University, Vernadsky Prospekt, 4, Simferopol 295007, Russia 9 V. M. Efetov Crimean Center for Oncology, Bespalova St. 45a, Simferopol 295008, Russia 10 Department of Urology, Rivne Regional Hospital, Rivne, Ukraine Knight of science

Quantum features of structured light

Abstract: The development of structured light affords new opportunities to exploit the spatial degrees of freedom for beams with wave-vector components transverse to the direction of propagation. This introduces an additional dimension to the information-conveying capacity of individual photons. However, several quantum issues of optical vortex interactions with detectors demand scrutiny. For any essentially paraxial vortex beam, while the spin and orbital parts of photon angular momentum are well defined, the corresponding quantum operators do not satisfy the proper commutation structure; for non-paraxial fields they are not even separable. In the local measurement of any such property of individual photons it is also important to recognize that absolute measurement is fundamentally compromised by the preclusion of a position operator, as is true for any relativistic quantum particle. Quantum uncertainty itself obviates the precise positional registration of any particular orbital angular momentum through any angle-specific aperture. Optical modes with marginally different directions of propagation cannot be discriminated with arbitrary precision: conservation of the summed orbital angular momentum, comprising a sum of optical and material elements, can only be ascertained in terms of expectation values. The orthogonality of optical states of a given beam wavelength and direction, but with different orbital angular momentum values, certainly affords extensive opportunities for quantum communication: the enhanced encoding of information per photon in a high-dimensionality transverse structure is, however, subject to both fundamental quantum and technical constraints.