School of Physics (Scholarly Articles)

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  • Publication
    Optical system of aplanatic telescope with a 100 m spherical primary mirror
    (Society of Photo-optical Instrumentation Engineers, 2022-06-30) Druzhin, Vladislav V.; Puryaev, Daniil T.; Goncharov, Alexander V.
    We propose an optical system of an extremely large telescope for ground-based or planetary use. The system comprises a segmented spherical mirror with a diameter of 100 m and f-number of f/1. There are three annular zones on the primary mirror, which corresponds to three annular telescopes (ATs) with f-numbers f/2, f/3.2, and f/5.2, all using a concave cardioidal secondary mirror with a maximum diameter of 3.18 m. This two-mirror system satisfies Fermat¿s principle and the Abbe¿s sine condition. The central zone of the primary mirror with a diameter of 23.8 m is used for the central three-mirror telescope, which is based on an afocal two-mirror system with a convex aspheric secondary mirror with a diameter of 3 m. Four possible configurations are presented for the central telescope, which makes it possible to vary the f-number in a wide range with design examples given for f/1, f/4.2, f/14, and f/33 systems. The ATs form three coherent images of the same astronomical object, which offers possibilities of simultaneous observations at three different wavelengths or image processing of a combined image with enhanced angular resolution. The main goal of the paper is to investigate the properties of new optical systems for ground-based and space telescopes with a fast spherical primary mirror for which aberration correction is achieved with a minimum number of auxiliary aspheric mirrors near the prime focus.
  • Publication
    Framework for developing an exposure science curriculum as part of the European Exposure Science Strategy 2020–2030
    (Elsevier, 2022-08-20) Connolly, Alison; Scheepers, Paul T. J.; Coggins, Marie; Vermeire, Theo; van Tongeren, Martie; Heinemeyer, Gerhard; Bridges, James W.; Bredendiek-Kämper, Susanne; Bruinen de Bruin, Yuri; Clayson, Anne; Gerding, Johannes; McCourt, Josephine; Urbanus, Jan; Viegas, Susana; von Goetz, Natalie; Zare-Jeddi, Maryam; Fantke, Peter
    Background Evaluating and managing exposures to chemical, physical and biological stressors, which frequently interplay with psychological stressors as well as social and behavioural aspects, is crucial for protecting human and environmental health and transitioning towards a sustainable future. Advances in our understanding of exposure rely on input from well-trained exposure scientists. However, no education programmes in Europe are currently explicitly dedicated to cover the broader range of exposure science approaches, applications, stressors and receptors. Objective To address this challenge, a curriculum is needed that yields credible, well-defined career pathways in exposure science. Methods Needs and conditions for advancing exposure science education in Europe were identified. As a starting point for a way forward, harmonised learning outcomes for exposure science were defined at each level of the European Qualifications Framework. The course programme coordinators were recruited for three varying courses, with respect to the course level and the proportion of the curriculum dedicated to exposure science. These courses were assessed via our systematic course review procedure. Finally, strategic objectives and actions are proposed to build exposure science education programmes. Results The ISES Europe `Education, Training and Communication¿ expert working group developed a framework for creating a viable exposure science curriculum. Harmonised learning outcomes were structured under eight learning levels, categorised by knowledge, skills and competence. Illustrative case studies demonstrated how education providers integrated these learning outcomes for their educational context and aligned the overall exposure science curriculum. Conclusions The international recognition and adoption of exposure science education will enable advances in addressing global exposure science challenges for various stressors, from behavioural aspects from individual to population scale, and effective communication between exposure scientists and relevant stakeholders and policy makers, as part of the European Exposure Science Strategy 2020¿2030.
  • Publication
    Halogenated flame retardants in Irish waste polymers: Concentrations, Legislative compliance, and preliminary assessment of temporal trends
    (Elsevier, 2022-07-20) Drage, Daniel; Sharkey, Martin; Al-Omran, Layla Salih; Stubbings, William A.; Berresheim, Harald; Coggins, Marie; Rosa, André Henrique; Harrad, Stuart; Environmental Protection Agency
    Halogenated flame retardants (HFRs) were measured in 470 waste plastic articles from Ireland between 2019 and 2020. We identified articles containing concentrations of polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCDD), and tetrabromobisphenol-A (TBBP-A) exceeding European Union limits. Enforcement of existing limits of 1000 mg/kg will render an estimated 3.1% (2800 t) of articles in the waste categories studied unrecyclable, increasing to: 4.0, 4.9, and 5.6% if limits were reduced to 500, 200, and 100 mg/kg respectively. Meanwhile, enforcing limits of 1,000, 500, 200, and 100 mg/kg will respectively remove 78, 82, 84, and 85% of PBDEs, HBCDD, and TBBP-A present in such waste. Other FRs targeted were detected infrequently and predominantly at very low concentrations. However, 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine (TTBP-TAZ) was detected in 3 display/IT product samples at 14,000 to 32,000 mg/kg, indicating elevated concentrations of FRs used as alternatives to PBDEs and HBCDD, will likely increase in future. Comparison with data for Ireland in 2015–16, revealed concentrations and exceedances of limits for PBDEs, HBCDD, and TBBP-A were similar or have declined. For end-of-life vehicle fabrics and foams, HBCDD and ΣPBDE concentrations declined significantly (p < 0.05) since 2015–16. Moreover, ΣPBDE concentrations in waste small domestic appliances are significantly lower in 2019–20, with a similarly significant decline for TBBP-A in waste IT and telecommunications articles. In contrast, HBCDD concentrations in waste extruded polystyrene increased significantly between 2015–16 and 2019–20. For other waste categories studied, no statistically significant temporal trends are evident (p > 0.05). Fewer samples exceeded PBDE and HBCDD limits in 2019–20 (7.8%) than 2015–16 (8.7%), while exceedances for TBBP-A fell from 2.4% in 2015–16 to 0.57% in 2019–20. While comparison between the 2015–16 and 2019-20 datasets provide a preliminary indication of changes, further monitoring is required if the impact of legislation designed to eliminate HFRs from the waste stream is to be fully evaluated.
  • Publication
    The invisible barrier to safe textile recycling
    (Frontiers Media, 2022-06-14) Sharkey, Martin; Coggins, Marie
    Presence of certain chemical additives (e.g. halogenated flame retardants, perfluoroalkyl substances, and phthalates) could hinder textile recycling operations as their presence renders end-of-life materials as “hazardous” and therefore not recyclable; • In 2018, there was an estimated minimum of 1.7 million tonnes of hazardous and unrecyclable textile waste generated in the EU; • Blanket-bans on classes of chemicals would likely be partially effective in reducing environmental uptake of and human exposure to harmful chemicals, but could also lead to increased use of “regrettable substitutions” with unforeseen implications; • Legislative restrictions on chemicals must be accompanied with reduction in demand: reducing volume of textile waste generated by reducing volume consumed, thus eliminating necessity for huge volume of chemical additives in the first instance.
  • Publication
    Indoor air quality, thermal comfort and ventilation in deep energy retrofitted Irish dwellings
    (Elsevier, 2022-05-28) Coggins, Ann Marie; Wemken, Nina; Kumar Mishra, Asit; Sharkey, Martin; Horgan, Liam; Cowie, Hilary; Bourdin, Emmanuel; McIntyre, Brian; Sustainable Energy Authority of Ireland (SEAI); Irish Environmental Protection Agency (EPA)
    Residential building stock energy retrofits will play a key role in EU climate actions. The impact of these retrofits on indoor air quality (IAQ) and occupant comfort needs to be assessed to inform future renovation programmes. This study evaluated IAQ and occupant satisfaction in a sample (n = 14) of deep energy retrofitted Irish residences, at least 12 months post retrofit. Measurements of PM2.5, formaldehyde, total volatile organic compounds (TVOCs), carbon monoxide, radon, and carbon dioxide were made in the main bedroom and living area over a period of two days to three months (depending on the pollutant). Temperature and humidity in most homes were within design comfort limits. Higher concentrations of all pollutants were measured in bedrooms. Only 30% of bedroom data met EN16798 Category I limits for CO2 (within 380 ppm of outdoor concentrations), suggesting that bedrooms maybe under ventilated. Median formaldehyde concentrations of 25.4 and 20.7 ¿g/m3 were detected in bedroom and living rooms respectively, with building materials likely being the major source. All radon data (apart from one home located in a high radon area) was less than the national reference value of 200 Bq/m3. Measured ventilation extract flow rates in most participating homes would not meet the minimum performance requirements in Irish Regulations of 2019 ¿ introduced post completion of the retrofits in this study. Greater compliance with the ventilation requirements of retrofits and the promotion and use of low emitting construction materials are recommended.
  • Publication
    Characterization of an amplified piezoelectric actuator for multiple reference optical coherence tomography
    (Optica, 2018-08-30) O'Gorman, Sean; Neuhaus, Kai; Alexandrov, Sergey; Hogan, Josh; Wilson, Carol; McNamara, Paul M.; Leahy, Martin
    The characterization of an amplified piezoelectric actuator (APA) as a new axial scanning method for multiple-reference optical coherence tomography (MR-OCT) is described. MR-OCT is a compact optical imaging device based on a recirculating reference-arm-scanning optical delay using a partial mirror that can enhance the imaging depth range by more than 10 times the reference mirror’s scanning amplitude. The scanning amplitude of the used APA was varied between 30 μm and 250 μm, depending on the scanning frequency of between 0.8 kHz and 1.2 kHz. A silver-coated miniature mirror was attached to the APA via ultraviolet-cured optical adhesive, and the light source was a super-luminescent diode with 1310 nm center wavelength and 56 nm bandwidth. The sensitivity was measured with and without the partial mirror in the reference delay line as a function of scan speed, frequency, and range, therefore providing results for MR-OCT and TD-OCT modes. It was found that the APA provides more than twice the mechanical scanning range compared to other opto-mechanic actuators, but results indicate degradation of signal-to-noise ratio and sensitivity at larger imaging depths. In conjunction with MR-OCT, the scan range of maximum 200 μm can be enhanced up to 1–1.5 mm by using a reduced amount of orders of reflections, which could be of interest to increase sensitivity in the future.
  • Publication
    Feasibility of correlation mapping optical coherence tomography angiographic technique using a 200 kHz vertical-cavity surface-emitting laser source for in vivo microcirculation imaging applications
    (Optica, 2018-08-01) Lal, Cerine; Subhash, Hrebesh M.; Alexandrov, Sergey; Leahy, Martin J.
    Optical coherence tomography (OCT) angiography is a well-established in vivo imaging technique to assess the overall vascular morphology of tissues and is an emerging field of research for the assessment of blood flow dynamics and functional parameters such as oxygen saturation. In this study, we present a modified scanning-based correlation mapping OCT using a 200 kHz high-speed swept-source OCT system operating at 1300 nm and demonstrate its wide field-imaging capability in ocular angiographic studies. (C) 2018 Optical Society of America
  • Publication
    Interference method for determination of the refractive index and thickness
    (Society of Photo-optical Instrumentation Engineers, 2000-09-01) Alexandrov, Sergey; Chernyh, Igor V.
    The interference method for simultaneous measurement of the absolute refractive index and the thickness of plane parallel samples is developed. This method enables us to test solid (including optical glasses, crystals, plastics, and other sheet materials), liquid, and gaseous media over a wide spectral range. The experimental model for the realization of this method, the laser interference refractometer and thicknessmeter (IRT), is manufactured and investigated. The IRT accuracy of the refractive index measurement is not worse than that of the best modern goniometers and the accuracy of the thickness measurement corresponds to the interference accuracy
  • Publication
    Functional imaging for regenerative medicine
    (BMC, 2016-04-19) Leahy, Martin; Thompson, Kerry; Zafar, Haroon; Alexandrov, Sergey; Foley, Mark; O’Flatharta, Cathal; Dockery, Peter
    In vivo imaging is a platform technology with the power to put function in its natural structural context. With the drive to translate stem cell therapies into pre-clinical and clinical trials, early selection of the right imaging techniques is paramount to success. There are many instances in regenerative medicine where the biological, biochemical, and biomechanical mechanisms behind the proposed function of stem cell therapies can be elucidated by appropriate imaging. Imaging techniques can be divided according to whether labels are used and as to whether the imaging can be done in vivo. In vivo human imaging places additional restrictions on the imaging tools that can be used. Microscopies and nanoscopies, especially those requiring fluorescent markers, have made an extraordinary impact on discovery at the molecular and cellular level, but due to their very limited ability to focus in the scattering tissues encountered for in vivo applications they are largely confined to superficial imaging applications in research laboratories. Nanoscopy, which has tremendous benefits in resolution, is limited to the near-field (e.g. near-field scanning optical microscope (NSNOM)) or to very high light intensity (e.g. stimulated emission depletion (STED)) or to slow stochastic events (photo-activated localization microscopy (PALM) and stochastic optical reconstruction microscopy (STORM)). In all cases, nanoscopy is limited to very superficial applications. Imaging depth may be increased using multiphoton or coherence gating tricks. Scattering dominates the limitation on imaging depth in most tissues and this can be mitigated by the application of optical clearing techniques that can impose mild (e.g. topical application of glycerol) or severe (e.g. CLARITY) changes to the tissue to be imaged. Progression of therapies through to clinical trials requires some thought as to the imaging and sensing modalities that should be used. Smoother progression is facilitated by the use of comparable imaging modalities throughout the discovery and trial phases, giving label-free techniques an advantage wherever they can be used, although this is seldom considered in the early stages. In this paper, we will explore the techniques that have found success in aiding discovery in stem cell therapies and try to predict the likely technologies best suited to translation and future directions.
  • Publication
    Synthetic aperture Fourier holographic optical microscopy
    (American Physical Society, 2006-10-18) Alexandrov, Sergey; Hillman, Timothy R.; Gutzler, Thomas; Sampson, David D.
    We report a new synthetic aperture optical microscopy in which high-resolution, wide-field amplitude and phase images are synthesized from a set of Fourier holograms. Each hologram records a region of the complex two-dimensional spatial frequency spectrum of an object, determined by the illumination field’s spatial and spectral properties and the collection angle and solid angle. We demonstrate synthetic microscopic imaging in which spatial frequencies that are well outside the modulation transfer function of the collection optical system are recorded while maintaining the long working distance and wide field of view.
  • Publication
    Microscopic particle discrimination using spatially-resolved Fourier-holographic light scattering angular spectroscopy
    (Optica, 2006-11-13) Hillman, Timothy R.; Alexandrov, Sergey; Gutzler, Thomas; Sampson, David D.
    We utilize Fourier-holographic light scattering angular spectroscopy to record the spatially resolved complex angular scattering spectra of samples over wide fields of view in a single or few image captures. Without resolving individual scatterers, we are able to generate spatially-resolved particle size maps for samples composed of spherical scatterers, by comparing generated spectra with Mie-theory predictions. We present a theoretical discussion of the fundamental principles of our technique and, in addition to the sphere samples, apply it experimentally to a biological sample which comprises red blood cells. Our method could possibly represent an efficient alternative to the time-consuming and laborious conventional procedure in light microscopy of image tiling and inspection, for the characterization of microscopic morphology over wide fields of view.
  • Publication
    Audio frequency in vivo optical coherence elastography
    (IOP Publishing, 2009-05-06) Adie, Steven G.; Kennedy, Brendan F.; Armstrong, Julian J.; Alexandrov, Sergey; Sampson, David
    We present a new approach to optical coherence elastography (OCE), which probes the local elastic properties of tissue by using optical coherence tomography to measure the effect of an applied stimulus in the audio frequency range. We describe the approach, based on analysis of the Bessel frequency spectrum of the interferometric signal detected from scatterers undergoing periodic motion in response to an applied stimulus. We present quantitative results of sub-micron excitation at 820 Hz in a layered phantom and the first such measurements in human skin in vivo.
  • Publication
    High-resolution, wide-field object reconstruction with synthetic aperture Fourier holographic optical microscopy
    (Optica, 2009) Hillman, Timothy R.; Gutzler, Thomas; Alexandrov, Sergey; Sampson, David
    We utilize synthetic-aperture Fourier holographic microscopy to resolve micrometer-scale microstructure over millimeter-scale fields of view. Multiple holograms are recorded, each registering a different, limited region of the sample object’s Fourier spectrum. They are “stitched together” to generate the synthetic aperture. A low-numerical-aperture (NA) objective lens provides the wide field of view, and the additional advantages of a long working distance, no immersion fluids, and an inexpensive, simple optical system. Following the first theoretical treatment of the technique, we present images of a microchip target derived from an annular synthetic aperture (NA = 0.61) whose area is 15 times that due to a single hologram (NA = 0.13); they exhibit a corresponding qualitative improvement. We demonstrate that a high-quality reconstruction may be obtained from a limited sub-region of Fourier space, if the object’s structural information is concentrated there.
  • Publication
    Three-dimensional depth-resolved and extended-resolution micro-particle characterization by holographic light scattering spectroscopy
    (Optica, 2010) Gutzler, Thomas; Hillman, Timothy R.; Alexandrov, Sergey; Sampson, David D.
    Fourier-holographic light scattering spectroscopy is applied to record complex angular scattering spectra of two- and three-dimensional samples over a wide field of view. We introduce a computational depth sectioning technique and, for the first time, demonstrate that a single-exposure hologram can generate a quantitative, three-dimensional map of particle sizes and locations over several cubic millimeters with micrometer resolution. Such spatially resolved maps of particle sizes are generated by Mie-inversion and could not be ascertained from the directly reconstructed intensity-distribution images. We also demonstrate synthesis of multiple angular scattering intensity spectra to increase the angular range and improve size detection sensitivity.
  • Publication
    Real-time quantitative visualization of 3D structural information
    (Optica, 2012) Alexandrov, Sergey; Uttam, Shikhar; Bista, Rajan K.; Zhao, Chengquan; Liu, Yang
    We demonstrate a novel approach for the real time visualization and quantification of the 3D spatial frequencies in an image domain. Our approach is based on the spectral encoding of spatial frequency principle and permits the formation of an image as a color map in which spatially separated spectral wavelengths correspond to the dominant 3D spatial frequencies of the object. We demonstrate that our approach can visualize and analyze the dominant axial internal structure for each image point in real time and with nanoscale sensitivity to structural changes. Computer modeling and experimental results of instantaneous color visualization and quantification of 3D structures of a model system and biological samples are presented.
  • Publication
    Spectral encoding of spatial frequency approach for characterization of nanoscale structures
    (American Institute of Physics, 2012-07-17) Alexandrov, Sergey; Uttam, Shikhar; Bista, Rajan K.; Staton, Kevin; Liu, Yang
    An approach to acquire axial structural information at nanoscale is demonstrated. It is based on spectral encoding of spatial frequency principle to reconstruct the structural information about the axial profile of the three-dimensional (3D) spatial frequency for each image point. This approach overcomes the fundamental limitations of current optical techniques and provides nanoscale accuracy and sensitivity in characterizing axial structures. Numerical simulation and experimental results are presented. We acknowledge the funding support from National Cancer Institute (CA152935, CA164433) and thank Donna Stolz and the staff at Center for Biologic Imaging at University of Pittsburgh for their help with TEM imaging.
  • Publication
    Simultaneous en-face imaging of multiple layers with multiple reference optical coherence tomography
    (Society of Photo-optical Instrumentation Engineers, 2017-08-22) Neuhaus, Kai; O’Gorman, Seán; McNamara, Paul M.; Alexandrov, Sergey; Hogan, Josh; Wilson, Carol; Leahy, Martin J.
    A technique based on multiple reference optical coherence tomography (MR-OCT) is proposed for simultaneous imaging at multiple depths. The technique has been validated by imaging a reference sample and a fingerprint in-vivo. The principle of scanning multiple selected layers is shown by imaging a partial fingerprint with 200 x 200 x 200 voxels of 3 x 3 x 0.5 mm size and obtaining an arbitrary amount of layers merely by digital processing. The spacing among the layers can be adjusted arbitrarily, and the SNR roll-off is shown for three different spacings. At a mirror scan frequency of 1 kHz and an A-line rate of 2 kHz, the acquisition time was 20 s for one volume. The results show the feasibility of the application of layer scanning MR-OCT that uses a partial mirror in the reference arm of the Michelson interferometer. The reduced scan range required for layer scanning allows even higher scan rates that are limited only by the voice coil design and the mass-spring system, e.g., mirror mass, spring constant, and damping. (c) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)
  • Publication
    Label-free ultra-sensitive visualization of structure below the diffraction resolution limit
    (Wiley, 2018-03-23) Alexandrov, Sergey; McGrath, James; Sheppard, Colin J. R.; Boccafoschi, Francesca; Giannini, Cinzia; Sibillano, Teresa; Subhash, Hrebesh; Hogan, Josh; Leahy, Martin; National University of Ireland, Galway; University of Limerick; European Union
    For both fundamental study of biological processes and early diagnosis of diseases, information about nanoscale changes in tissue and cell structure is crucial. Nowadays, almost all currently known nanoscopy methods rely upon the contrast created by fluorescent stains attached to the object or molecule of interest. This causes limitations due to the impact of the label on the object and its environment, as well as its applicability in vivo, particularly in humans. In this paper, a new label-free approach to visualize small structure with nano-sensitivity to structural alterations is introduced. Numerically synthesized profiles of the axial spatial frequencies are used to probe the structure within areas whose size can be beyond the diffraction resolution limit. Thereafter, nanoscale structural alterations within such areas can be visualized and objects, including biological ones, can be investigated with sub-wavelength resolution, in vivo, in their natural environment. Some preliminary results, including numerical simulations and experiments, which demonstrate the nano-sensitivity and super-resolution ability of our approach, are presented.
  • Publication
    Simple characterization scheme for optical coherence tomography systems with application to a commercial and a near-isometric resolution fibre-based system
    (2021-12-14) Dey, Rajib; Zhou, Yi; Neuhaus, Kai; Alexandrov, Sergey; Nolan, Andrew; Chang, Ting-Chiao; Leahy, Martin; Horizon 2020
    Optical Coherence Tomography (OCT) is a rapidly growing imaging modality in biomedical optics. OCT can perform high-resolution, cross-sectional imaging of the microstructure of biological tissues by measuring the coherent spectrum from the backscattered light. OCT systems with broad spectral bandwidths are often constructed using free-space optics to avoid dispersion by fibre optic components. This paper presents a fibre-based OCT system at a centrewavelength of 1300nmwith an axial resolution of 3.8 ¿m in air, surpassing any previously reported values to the best of our knowledge. Despite the challenges in transporting a broadband spectrum using fibre-optics, the system investigation was motivated by the ever-increasing demand for commercialization of high-resolution OCT systems and simplification of construction. We also evaluate and demonstrate the direct measurement method for axial resolution using an air wedge. Imaging of biomedical and other samples is demonstrated using a high numerical aperture sample lens and compared with images from a commercial OCT system. We discuss the effect of the improved structural visibility by achieving image voxels closer to an isometric shape with a high NA sample lens.
  • Publication
    Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) in human milk from Ireland: temporal trends and implications for nursing infant exposure
    (OAE Publishing Inc, 2021-11-19) Houlihan, Margarete; Wemken, Nina; Keogh, Myra; O’Riordain, Colman; Noone, Conor; Tierney, Julie; Claire Cellarius, Claire; Cleere, Kathy; Morrison, John J.; Daly, Sean; Harrad, Stuart; Tlustos, Christina; Coggins, Marie Ann; Environmental Protection Agency (EPA), Ireland; Food Safety Authority of Ireland
    Aim: The elucidation of temporal trends in human exposure to polychlorinated biphenyls (PCBs) and 17 polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) since the previous Irish human milk surveys and to evaluate the impacts of legislative bans and restrictions on human exposure to these compounds. Methods: Concentrations of PCBs and 17 PCDD/Fs were measured in 16 pools of human milk collected from 92 Irish primiparas participating in the Irish EPA-funded ELEVATE project between October 2016 and April 2018, using Gas-Chromatography coupled with Mass spectrometry. Results: The geometric mean upper bound concentration of 16 pooled human milk samples [PCDD/Fs + dioxin-like (dl)-PCB TEQ; 4.5 ng kg-1 lipid weight] are on the lower end of those reported internationally. WHO-TEQ PCDD/Fs + dl-PCB are significantly lower (P