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  • Journal article
    Hong W, Dunsby C, 2022,

    Automatic Tube Lens Design from Stock Optics for Microscope Remote-refocussing Systems

    , Optics Express
  • Journal article
    Byrnes N, Foreman MR, 2022,

    Polarisation statistics of vector scattering matrices from the circular orthogonal ensemble

    , Optics Communications, Vol: 503, Pages: 1-6, ISSN: 0030-4018

    We study the polarisation properties of random𝑁×𝑁scattering matrices distributed according to the circularorthogonal ensemble. We interpret 2×2 sub-blocks of the scattering matrix as Jones matrices and study theirstatistical properties. Using the polar decomposition, we derive probability density functions for retardanceand diattenuation from scattering matrices of arbitrary size and in the limit𝑁→∞.

  • Journal article
    Lee H, Berk J, Webster A, Kim D, Foreman MRet al., 2021,

    Label-free detection of single nanoparticles with disordered nanoisland surface plasmon sensor.

    , Nanotechnology, ISSN: 0957-4484

    We report sensing of single nanoparticles using disordered metallic nanoisland substrates supporting surface plasmon polaritons (SPPs). Speckle patterns arising from leakage radiation of elastically scattered SPPs provides a unique fingerprint of the scattering microstructure at the sensor surface. Experimental measurements of the speckle decorrelation are presented and shown to enable detection of sorption of individual gold nanoparticles and polystyrene beads. Our approach is verified through bright-field and fluorescence imaging of particles adhering to the nanoisland substrate.

  • Journal article
    Chandran A, Battle RA, Murray RT, Runcorn T, Taylor JRet al., 2021,

    Watt-level 743 nm source by second-harmonic generation of a cascaded phosphosilicate Raman fiber amplifier

    , Optics Express, Vol: 29, Pages: 41467-41474, ISSN: 1094-4087

    We demonstrate a nanosecond pulsed 743 nm source through second-harmonic generation of a cascaded phosphosilicate Raman fiber amplifier system operating at 1485 nm. The amplifier is pumped by a 1240 nm phosphosilicate Raman fiber amplifier and seeded with a continuous-wave 1485 nm diode. This 1485 nm light is used for second-harmonic generation in periodically poled lithium niobate. Greater than 1 W of average power is generated at 743 nm with a corresponding pulse energy of 220 nJ at a repetition rate of 5 MHz. The source displays excellent beam quality (M2𝑥,𝑦 ≤ 1.18) with ideal parameters for biomedical imaging applications.

  • Journal article
    Fotiadi AA, Korobko DA, Zolotovskii IO, Taylor JRet al., 2021,

    Brillouin-like amplification in rare-earth-doped optical fibers

    , OPTICS EXPRESS, Vol: 29, Pages: 40345-40359, ISSN: 1094-4087
  • Journal article
    Guglielmi L, Heliot C, Kumar S, Alexandrov Y, Gori I, Papaleonidopoulou F, Barrington C, East P, Economou AD, French PMW, McGinty J, Hill CSet al., 2021,

    Smad4 controls signaling robustness and morphogenesis by differentially contributing to the Nodal and BMP pathways

  • Journal article
    Song H, Mehdi SR, Wu C, Li Z, Gong H, Ali A, Huang Het al., 2021,

    Underwater Spectral Imaging System Based on Liquid Crystal Tunable Filter

  • Journal article
    Wright T, Sparks H, Paterson C, Dunsby Cet al., 2021,

    Video-rate remote refocusing through continuous oscillation of a membrane deformable mirror

    , Journal of Physics: Photonics, Vol: 3, Pages: 1-14, ISSN: 2515-7647

    This paper presents the use of a deformable mirror (DM) configured to rapidly refocus a microscope employing a highnumerical aperture objective lens. An Alpao DM97-15 membrane DM was used to refocus a 40×/0.80 NA water-immersionobjective through a defocus range of -50 to 50 m at 26.3 sweeps per second. We achieved imaging with a mean Strehlmetric of > 0.6 over a field of view in the sample of 200×200 m2 over a defocus range of 77 m. We describe anoptimisation procedure where the mirror is swept continuously in order to avoid known problems of hysteresis associatedwith the membrane DM employed. This work demonstrates that a DM-based refocusing system could in the future be used inlight-sheet fluorescence microscopes to achieve video-rate volumetric imaging.

  • Journal article
    Kalita R, Flanagan W, Lightley J, Kumar S, Alexandrov Y, Garcia E, Hintze M, Barkoulas M, Dunsby C, French PMWet al., 2021,

    Single-shot phase contrast microscopy using polarisation-resolved differential phase contrast

    , JOURNAL OF BIOPHOTONICS, Vol: 14, ISSN: 1864-063X
  • Journal article
    Geberbauer J, Kerridge-Johns W, Damzen M, 2021,

    > 30 W vortex LG₀₁ or HG₁₀ laser using a modetransforming output coupler

    , Optics Express, Vol: 29, Pages: 29082-29094, ISSN: 1094-4087

    High-power vortex light generated directly from lasers will help drive theirapplications in material processing, optical manipulation, levitation, particle acceleration, andcommunications, but limited power has been achieved to date. In this work, we demonstraterecord vortex average power of 31.3 W directly from a laser, to the best of our knowledge,using an interferometric mode transforming output coupler to convert a fundamental modeNd:YVO4 laser into a LG01 vortex output. The vortex laser was Q-switched with up to 600 kHzpulse rate with a high slope efficiency of 62.5% and an excellent LG01 modal purity of 95.2%.We further demonstrate > 30W laser power in a high quality HG10 mode by simple adjustmentof the output coupler. Experimental investigations of varying output coupling transmission arecompared with theory. This successful implementation of the interferometric output coupler ina high power system demonstrates the suitability of the mode transforming method for robustturn-key vortex lasers with high efficiency and high modal purity, with scalable power andpulse rate.

  • Journal article
    Paraiso TK, Woodward R, Marangon DG, Lovic V, Yuan Z, Shields AJet al., 2021,

    Advanced Laser Technology for Quantum Communications (Tutorial Review)

  • Journal article
    Lightley J, Gorlitz F, Kumar S, Kalita R, Kolbeinsson A, Garcia E, Alexandrov Y, Bousgouni V, Wysoczanski R, Barnes P, Donnelly L, Bakal C, Dunsby C, Neil MAA, Flaxman S, French PMWet al., 2021,

    Robust deep learning optical autofocus system applied to automated multiwell plate single molecule localization microscopy

  • Journal article
    Berk J, Foreman MR, 2021,

    Role of multiple scattering in single particle perturbations in absorbing random media

    , Physical Review Research, Vol: 3, Pages: 1-14, ISSN: 2643-1564

    Speckle patterns produced by disordered scattering systems exhibit asensitivity to addition of individual particles which can be used for sensingapplications. Using a coupled dipole model we investigate how multiplescattering can enhance field perturbations arising in such random scatteringbased sensors. Three distinct families of multiple scattering paths are shownto contribute and the corresponding complex enhancement factors derived.Probability distributions of individual enhancement factors over the complexplane are characterised numerically within the context of surface plasmonpolariton scattering in which absorption is shown to play an important role. Weshow that enhancements become more strongly dependent on individual scattererproperties when absorption losses are larger, however, amplitude enhancements$\sim 10^2$, comparable to low loss surface plasmons, are achievable throughsensor optimisation. Approximate analytic expressions for the complex meanenhancements are also found, which agree well with simulations when loopcontributions are negligible.

  • Conference paper
    Garcia E, Lightley J, Kumar S, Kalita R, Gorlitz F, Alexandrov Y, Cook T, Dunsby C, Neil M, Roufosse C, French Pet al., 2021,

    Application of direct stochastic optical reconstruction microscopy (dSTORM) to the histological analysis of human glomerular disease

    , Publisher: SPRINGER, Pages: S142-S142, ISSN: 0945-6317
  • Journal article
    Gratus J, Seviour R, Kinsler P, Jaroszynski DAet al., 2021,

    Temporal boundaries in electromagnetic materials

    , NEW JOURNAL OF PHYSICS, Vol: 23, ISSN: 1367-2630
  • Journal article
    Berk J, Foreman MR, 2021,

    Theory of multiple scattering enhanced single particle plasmonic sensing

    , ACS Photonics, Vol: 8, Pages: 2227-2233, ISSN: 2330-4022

    Methods to increase the light scattered from small particles can help improve the sensitivity of many sensing techniques. Here, we investigate the role multiple scattering plays in perturbing the scattered signal when a particle is added to a random scattering environment. Three enhancement factors, parametrizing the effect of different classes of multiple scattering trajectories on the field perturbation, are introduced and their mean amplitudes explored numerically in the context of surface plasmon polariton scattering. We demonstrate that there exists an optimum scatterer density at which the sensitivity enhancement is maximized, with factors on the order of 102 achievable. Dependence of the enhancement factors on scatterer properties are also studied.

  • Journal article
    Pittaluga M, Minder M, Lucamarini M, Sanzaro M, Woodward RI, Li MJ, Yuan Z, Shields AJet al., 2021,

    600-km repeater-like quantum communications with dual-band stabilization

    , Nature Photonics, Vol: 15, Pages: 530-535, ISSN: 1749-4885

    Twin-field (TF) quantum key distribution (QKD) fundamentally alters the rate-distance relationship of QKD, offering the scaling of a single-node quantum repeater. Although recent experiments have demonstrated the new opportunities for secure long-distance communications allowed by TF-QKD, formidable challenges remain to unlock its true potential. Previous demonstrations have required intense stabilization signals at the same wavelength as the quantum signals, thereby unavoidably generating Rayleigh scattering noise that limits the distance and bit rate. Here, we introduce a dual-band stabilization scheme that overcomes past limitations and can be adapted to other phase-sensitive single-photon applications. Using two different optical wavelengths multiplexed together for channel stabilization and protocol encoding, we develop a setup that provides repeater-like key rates over communication distances of 555 km and 605 km in the finite-size and asymptotic regimes respectively and increases the secure key rate at long distance by two orders of magnitude to values of practical relevance.

  • Journal article
    De Marco I, Woodward RI, Roberts GL, Paraiso TK, Roger T, Sanzaro M, Lucamarini M, Yuan Z, Shields AJet al., 2021,

    Real-Time operation of a multi-rate, multi-protocol quantum key distribution transmitter

    , Optica, Vol: 8, Pages: 911-915, ISSN: 2334-2536

    Quantum key distribution (QKD) is the best candidate for securing communications against attackers, who may in the future exploit quantum-enhanced computational powers to break classical encryption. As such, new challenges are arising from our need for large-scale deployment of QKD systems. In a realistic scenario, transmitting and receiving devices from different vendors should be able to communicate with each other without the need for matching hardware. Therefore, practical deployment of QKD would require hardware capable of adapting to different protocols and clock rates. Here, we address this challenge by presenting a multi-rate, multi-protocol QKD transmitter linked to a correspondingly adaptable QKD receiver. The flexibility of the transmitter, achieved by optical injection locking, allows us to connect it with two receivers with inherently different clock rates. Furthermore, we demonstrate the multi-protocol operation of our transmitter, communicating with receiving parties employing different decoding circuits. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.

  • Journal article
    Berk J, Paterson C, Foreman MR, 2021,

    Tracking single particles using surface plasmon leakage radiation speckle

    , Journal of Lightwave Technology, Vol: 39, Pages: 3950-3960, ISSN: 0733-8724

    Label free tracking of small bio-particles such as proteins or viruses is of great utility in the study of biological processes, however such experiments are frequently hindered by weak signal strengths and a susceptibility to scattering impurities. To overcome these problems we here propose a novel technique leveraging the enhanced sensitivity of both interferometric detection and the strong field confinement of surface plasmons. Specifically, we show that interference between the field scattered by an analyte particle and a speckle reference field, derived from random scattering of surface plasmons propagating on a rough metal film, enables particle tracking with sub-wavelength accuracy. We present the analytic framework of our technique and verify its robustness to noise through Monte Carlo simulations.

  • Journal article
    Boland MA, Cohen EAK, Flaxman SR, Neil MAAet al., 2021,

    Improving axial resolution in Structured Illumination Microscopy using deep learning

  • Journal article
    Gong H, Guo W, Neil MAA, 2021,

    GPU-accelerated real-time reconstruction in Python of three-dimensional datasets from structured illumination microscopy with hexagonal patterns

  • Journal article
    Parmar V, Singh S, Kumar S, Vijaya Prakash G, Kalyanasundaram Det al., 2021,

    Thermo-physical modeling and experimental validation of core-shell nanoparticle fabrication of nickel-titanium (nitinol) alloy

    , Optics and Laser Technology, Vol: 138, ISSN: 0030-3992

    Nickel-titanium (nitinol) is a biocompatible shape memory alloy with hyperelasticity and biocompatibility property. A three-dimensional heat diffusion model was used in conjunction with phase explosion theory to explain the formation of core-shell nanoparticles of nitinol. The diffusion model was used to evaluate the melt-pool temperature in the ablation region, while the phase explosion theory was used to estimate the thermophysical expansion and subsequent fragmentation of molten and vaporized nitinol. The mathematical parameters were formulated in conjunction with the experimental results of pulsed laser ablation of core-shell nitinol nanoparticles of various sizes. The model was further employed to predict the sizes of the nanoparticles produced at other higher fluences and the results were experimentally validated.

  • Conference paper
    Geberbauer JWT, Kerridge-Johns WR, Damzen MJ, 2021,

    >30 W Vortex Laser Using Vortex Output Coupler

    Advances in vortex lasers with simplified robust designs that provide high purity vortex light with high power and efficiency, will help drive progress in material processing, communication and quantum technologies. We demonstrated in our earlier work [1] , [2] that a conventional laser, lasing on the fundamental Gaussian mode, can be converted to have a vortex output using a modified Sagnac ring, or vortex output coupler (VOC). This VOC provides handedness switchable LG 0±1 output, with variable output coupling. Here we report the highest average power vortex laser, to the best of our knowledge, operating in CW and Q-switched modes.

  • Conference paper
    Tawy G, Minassian A, Damzen MJ, 2021,

    8.5W Linear and 3.6W Ring TEM<inf>00</inf>Diode-Pumped Alexandrite Lasers

    Wavelength tunable and single frequency laser sources in the near-infrared are essential in addressing high resolution applications including Quantum Technologies and remote sensing. Alexandrite lasers are an attractive prospect for these applications owing to its broad emission in the near infrared (700-850 nm) and the commercial availability of high power and low-cost red-diode pumping for high efficiency laser operation in a compact system. Here, we present record-levels of TEM 00 power from diode-pumped Alexandrite linear and ring lasers.

  • Journal article
    Garcia E, Lightley J, Kumar S, Kalita R, Gorlitz F, Alexandrov Y, Cook T, Dunsby C, Neil MAA, Roufosse CA, French PMWet al., 2021,

    Application of direct stochastic optical reconstruction microscopy (dSTORM) to the histological analysis of human glomerular disease

  • Journal article
    Azeem F, Trainor LS, Devane PA, Norman DS, Rueda A, Lambert NJ, Kumari M, Foreman MR, Schwefel HGLet al., 2021,

    Dielectric perturbations: anomalous resonance frequency shifts in optical resonators

    , Optics Letters, Vol: 46, Pages: 2477-2480, ISSN: 0146-9592

    Small perturbations in the dielectric environment around resonant dielectric structures usually lead to a frequency shift of the resonator modes directly proportional to the polarizability of the perturbation. Here, we report experimental observations of strong frequency shifts that can oppose and even exceed the contribution of the perturbations’ polarizability. We show in particular how the mode frequencies of a lithium niobate whispering-gallery-mode resonator are shifted by planar substrates—of refractive indices ranging from 1.50 to 4.22—contacting the resonator rim. Both blue- and redshifts are observed, as well as an increase in mode linewidth, when substrates are moved into the evanescent field of the whispering gallery mode. We compare the experimental results to a theoretical model by Foreman et al. [J. Opt. Soc. Am. B 33, 2177 (2016) [CrossRef] ] and provide an additional intuitive explanation based on the Goos–Hänchen shift for the optical domain, with applications to dielectric structures ranging from meta-surfaces to photonic crystal cavities.

  • Journal article
    Cannon T, Lagarto J, Dyer B, Garcia Castano E, Kelly D, Peters N, Lyon A, French P, Dunsby Cet al., 2021,

    Characterisation of NADH fluorescence properties under one-photon excitation with respect to temperature, pH and binding to lactate dehydrogenase

    , Optical Society of America Continuum, Vol: 4, Pages: 1610-1625

    Reduced nicotinamide adenine dinucleotide (NADH) is the principal electron donor in glycolysis and oxidative metabolism and is thus recognized as a key biomarker for probing metabolic state. While the fluorescence characteristics of NADH have been investigated extensively, there are discrepancies in the published data due to diverse experimental conditions, instrumentation and microenvironmental parameters that can affect NADH fluorescence. Using a cuvette-based time-resolved spectrofluorimeter employing one-photon excitation at 375 nm, we characterized the fluorescence intensity, lifetime, spectral response, anisotropy and time-resolved anisotropy of NADH in aqueous solution under varying microenvironmental conditions, namely temperature, pH, and binding to lactate dehydrogenase (LDH). Our results demonstrate how temperature, pH, and binding partners each impact the fluorescence signature of NADH and highlight the complexity of the fluorescence data when different parameters produce competing effects. We hope that the data presented in this study will provide a reference for potential sources of variation in experiments measuring NADH fluorescence.

  • Journal article
    Gratus J, Kinsler P, McCall MW, 2021,

    Temporary Singularities and Axions: An Analytic Solution that Challenges Charge Conservation

    , ANNALEN DER PHYSIK, Vol: 533, ISSN: 0003-3804
  • Journal article
    Murray RT, Chandran AM, Battle RA, Runcorn TH, Schunemann PG, Zawilski KT, Guha S, Taylor JRet al., 2021,

    Seeded optical parametric generation in CdSiP2 pumped by a Raman fiber amplifier at 124  µm

    , Optics Letters, Vol: 46, Pages: 2039-2039, ISSN: 0146-9592

    We report a seeded optical parametric generator (OPG) producing tunable radiation from 4.2–4.6 µm. The seeded OPG employs a 13 mm long CdSiP2 (CSP) crystal cut for non-critical phase-matching, pumped by a nanosecond-pulsed, MHz repetition rate Raman fiber amplifier system at 1.24 µm. A filtered, continuous-wave fiber supercontinuum source at 1.72 µm is used as the seed. The source generates up to 0.25 W of mid-infrared (MIR) idler power with a total pump conversion of 42% (combined signal and idler).

  • Journal article
    Kerridge-Johns WR, Jaillot J-B, Damzen MJ, 2021,

    Sampling a vortex from a Gaussian beam using a wedge-plate shearing interferometer

    , Applied Optics, Vol: 60, Pages: 3510-3510, ISSN: 1559-128X

    Many vortex-generation techniques have been developed to address a range of potential applications, exploiting their unique amplitude and phase profiles and their possession of orbital angular momentum. In this work, we present what may be the simplest method of vortex beam generation, requiring only a wedged optic: the wedge-plate shearing interferometer (WPSI). We show that the WPSI can reflect a first order Laguerre–Gaussian vortex beam (LG01) with a theoretical purity of >99% from an input fundamental Gaussian beam, with 98% LG01 purity experimentally demonstrated. We demonstrate 1% power conversion with a route to 14%. The monolithic WPSI is a simple, compact, and highly stable device, which can operate at any wavelength that the material is transparent to. We anticipate that it will be useful where sampling a robust, high-purity vortex beam from a Gaussian laser beam is required, including low-cost vortex generation for metrology or education.

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