Light Spread Research Articles

Experimentally manipulating light spectra reveals the importance of dark corridors for commuting bats.

The rapid global spread of artificial light at night is causing unprecedented disruption to ecosystems. In otherwise dark environments, street lights restrict the use of major flight routes by some bats, including the threatened lesser horseshoe bat Rhinolophus hipposideros, and may disrupt foraging. Using radio tracking, we examined the response of individual female R.hipposideros to experimental street lights placed on hedgerows used as major flight routes. Hedgerows were illuminated on one side over four nights using lights with different emission spectra, while the opposite side of the hedge was not illuminated. Automated bat detectors were used to examine changes in overall bat activity by R.hipposideros and other bat species present. R.hipposideros activity reduced significantly under all light types, including red light, challenging a previously held assumption that red light is safe for bats. Despite this, R.hipposideros rapidly adapted to the presence of lights by switching their flight paths to the dark side of the hedgerow, enabling them to reach foraging sites without restriction. Red light had no effect on the activity of the other species present. Slow-flying Myotis spp. avoided orange, white and green light, while more agile Pipistrellus spp. were significantly more active at these light types compared to dark controls, most probably in response to accumulations of insect prey. No effect of any light type was found for Nyctalus or Eptesicus spp. Our findings demonstrate that caution must be used when promoting forms of lighting that are thought to be safe for wildlife before they are tested more widely. We argue that it is essential to preserve dark corridors to mitigate the impacts of artificial light at night on bat activity and movements.

Characterization or Monolithic Scintillation Detectors Etched with Laser Induced Optical Barriers.

Several groups are actively investigating the performance of monolithic (continuous) scintillation detectors using a variety of crystal thicknesses, photo-sensor configurations, and surface treatments. This work explores the performance of thick LYSO crystals that would be applicable to a whole-body PET system. The crystals were etched with laser induced optical barriers (LIOBs) to alter the behavior of the light spread within the crystal in order to improve the performance of the detector. We studied the behavior of the LIOBs in response to optical light using small cubes of LYSO with a variety of laser etching parameters to characterize the impact of the optical barriers. We demonstrated that the opacity of the etchings can be altered by varying the parameters of the laser etching, which influences the depth-dependent light response and spatial resolution in the thick crystal. We successfully etched several crystals, as large as 50×50×25-mm3 thick, with a fine grid of LIOBs, and achieved an average spatial resolution close to 3 mm (FWHM) with 511-keV gammas.

Modelling the Distribution of Lasers in Biological Tissues

For the time being there is no accurate theory about the spread of light in a structurally non-homogeneous medium whereas the experimental research is additionally hindered because of the necessity to maintain constant structural-dynamic parameters. In this respect numerical modelling of the processes of spreading of laser radiation plays increasingly important role.

Nuclear Star Clusters in Cosmological Simulations

Abstract We investigate the possible connection between the most massive globular clusters, such as ω Cen and M54, and nuclear star clusters (NSCs) of dwarf galaxies that exhibit similar spreads in age and metallicity. We examine galactic nuclei in cosmological galaxy formation simulations at z ≈ 1.5 to explore whether their age and metallicity spreads could explain these massive globular clusters. We derive structural properties of these nuclear regions, including mass, size, rotation, and shape. By using theoretical supernova yields to model the supernova enrichment in the simulations, we obtain individual elemental abundances for Fe, O, Na, Mg, and Al. Our nuclei are systematically more metal-rich than their host galaxies, which lie on the expected mass–metallicity relation. Some nuclei have a spread in Fe and age comparable to the massive globular clusters of the Milky Way, lending support to the hypothesis that NSCs of dwarf galaxies could be the progenitors of these objects. None of our nuclear regions contain the light element abundance spreads that characterize globular clusters, even when a large age spread is present. Our results demonstrate that extended star formation history within clusters, with metal pollution provided solely by supernova ejecta, is capable of replicating the metallicity spreads of massive globular clusters, but still requires another polluter to produce the light element variations.

Sharp Multiple-Phase Resonances in a Plasmonic Compound Grating With Multislits

Transmission properties of light through a plasmonic grating with multislits are investigated. The results show that sharp phase resonance (PR) and multiphase resonance (MPR) for each mode at multiple frequencies are achieved and effectively tailored only by adjusting the slight difference of the multislit widths; the values of the PR dips are almost zero. Based on the field distributions, Fabry-Perot-resonant and phase-resonant mechanisms have been suggested for the physical origins of the observations qualitatively. In addition, we can realize the control of light spreading through an arbitrary slit; a multichannel selector is modeled and described. Compared with the conventional plasmonic compound grating, this multislit grating with different slit widths has obvious advantages, such as simple structure, single material composition, and better realizability. PR and MPR can be achieved at multiple frequencies.

Light beam interactions and emission performance in powder phosphor materials: The role of the binder

Abstract The light emission performance of powder phosphors, employed in a variety of imaging applications, is affected by their structural (i.e., the particle size and packing) and optical properties (i.e., the wavelength of the light rays and the refractive index of the grains). In the chemical synthesis and the corresponding construction development of phosphor layers, the binder plays crucial role though its contribution to the way that the grains are glued together in a packed spatial distribution. In the present work, the influence of the binder on optical diffusion models was examined by using Mie theory and Monte Carlo simulation. To this aim, phosphor layers were investigated assuming different set-ups of refractive indexes (i.e., four cases of phosphor grains and binder combinations). Results showed that the choice of the binder affects the amount and distribution of light mainly through the: (i) domination of light absorption with respect to light scattering, and (ii) the direction of the light beam when light scattering takes place. It is important to note that by changing the refractive index of the binding material the light spread was not considerably varied through the number of light-grain interactions.

The Science of Light Engineering, Fields of Application and Theoretical Foundations

The article discussed two important problems, which have not been addressed previously: – The conceptual interpretation of lighting engineering, and the expansion of its definition beyond illumination, which has became widely accepted. An expanded concept of lighting engineering proposed by the authors includes all fields of application of optical radiation (light): illumination, irradiation, phototherapy (light therapy), light alarm systems, light location, light design, etc; – The problem of developing the theoretical foundation of Lighting Engineering. Differences between three existing light theories are summarised. The first one is quantum theory, explaining all known light phenomena. The second one is wave theory based on the provision that light spreads in waves. The third theory is beam and photometric based on the light field theory, which is the most widely applied and simple for practical calculations and simulation.

Performance of pixelated CsI scintillation screen with hexagonal array arrangement prepared by vacuum melting injection method

The pixelated scintillation screen as an important component of the X-ray imaging detector effectively solves the issue of the lateral spreading of scintillation light and improves the spatial resolution of X-ray imaging. In this work, the hexagonal as well as square arranged pixelated CsI scintillation screens based on the silicon pore templates with pore pitch about 4μm and diameter about 3μm were fabricated by vacuum melting injection method. The morphology, crystallinity, X-ray excited optical luminescence and X-ray imaging performance of the screens were investigated. The results show that the CsI scintillator was filled into the silicon pore templates uniformly and compactly without microbubbles even if the depth of the filled CsI microcolumns reaches 100μm. The pixelated scintillation screen exhibits good CsI crystallinity with (110) preferred orientation. The intensity of X-ray excited optical luminescence of the hexagonal arranged pixelated CsI scintillation screen increases by 14.3% compared with that of the square arranged screen with same thickness. Furthermore, the intensity of the pixelated CsI screen with 100μm thickness is 34.1% higher than that of the screen with 40μm thickness. The spatial resolution of the X-ray imaging system with the hexagonal arranged pixelated CsI scintillation screen is about 115 lp/mm and not sensitive to the screen thickness, which is 11.5% higher than that with the square arranged screen. The detective quantum efficiency of the system with the hexagonal arranged pixelated CsI scintillation screen appears relatively higher than that with the square arranged screen with same thickness and increases with the thickness of the screen. This means the X-ray imaging performance of the hexagonal arranged pixelated CsI scintillation screen is better than that of the square array arranged screen.

Correlation spreading and properties of the quantum state in quench dynamics.

The light cone spreading of correlations following a quantum quench is obtained from first principles. Fully taking into account quantum and interaction effects, the derivation shows how light cone dynamics does not require peculiar properties of the postquench state.

Resonant-light diffusion in a disordered atomic layer

Light scattering in dense media is a fundamental problem of many-body physics, which is also relevant for the development of optical devices. In this work we investigate experimentally light propagation in a dense sample of randomly positioned resonant scatterers confined in a layer of sub-wavelength thickness. We locally illuminate the atomic cloud and monitor spatially-resolved fluorescence away from the excitation region. We show that light spreading is well described by a diffusion process, involving many scattering events in the dense regime. For light detuned from resonance we find evidence that the atomic layer behaves as a graded-index planar waveguide. These features are reproduced by a simple geometrical model and numerical simulations of coupled dipoles.

Quantitative diagnosis of tissue microstructure with wide-field high spatial frequency domain imaging.

Non-contact and minimally invasive endoscopic optical imaging is an invaluable diagnostic tool for tissue examination and cancer screening. The point sampling techniques with high sensitivity to the tissue microenvironment are time consuming and often not affordable in clinics. There is a major clinical need for a large field-of-view (FOV) rapid screening method to highlight subtle tissue microstructural alterations. To address this unmet need, we have developed High Spatial Frequency Domain Imaging (HSFDI)-a non-contact imaging modality that spatially maps the tissue microscopic scattering structures over a large field of view (>1cm2). Based on an analytical reflectance model of sub-diffusive light from forward-peaked highly scattering media, HSFDI quantifies the spatially-resolved parameters of the light scattering phase function (i.e., the backscattering probability and the light spreading length) from the reflectance of structured light modulated at high spatial frequencies. Enhanced signal to noise ratio (SNR) is achieved at even ultra-high modulation frequencies with single snapshot multiple frequency demodulation (SSMD). The variations in tissue microstructures, including the strength of the background (pudding) refractive index fluctuation and the prominent scattering structure (plum) morphology, can then be inferred. After validation with optical phantoms, measurements of fresh ex vivo tissue samples revealed significant contrast and differentiation of the phase function parameters between different types and disease states (normal, inflammatory, and cancerous) of tissue whereas tissue absorption and reduced scattering coefficients only show modest changes. HSFDI may provide wide-field images of microscopic structural biomarkers unobtainable with either diffuse light imaging or point-based optical sampling. Potential clinical applications include the rapid screening of excised tissue and the noninvasive examination of suspicious lesions during operation.

Simulation the spatial resolution of an X-ray imager based on zinc oxide nanowires in anodic aluminium oxide membrane by using MCNP and OPTICS Codes

The spatial resolution of a detector is a very important parameter for x-ray imaging. A bulk scintillation detector because of spreading of light inside the scintillator does't have a good spatial resolution. The nanowire scintillators because of their wave guiding behavior can prevent the spreading of light and can improve the spatial resolution of traditional scintillation detectors. The zinc oxide (ZnO) scintillator nanowire, with its simple construction by electrochemical deposition in regular hexagonal structure of Aluminum oxide membrane has many advantages. The three dimensional absorption of X-ray energy in ZnO scintillator is simulated by a Monte Carlo transport code (MCNP). The transport, attenuation and scattering of the generated photons are simulated by a general-purpose scintillator light response simulation code (OPTICS). The results are compared with a previous publication which used a simulation code of the passage of particles through matter (Geant4). The results verify that this scintillator nanowire structure has a spatial resolution less than one micrometer.

Universal Broadening of the Light Cone in Low-Temperature Transport.

We consider the low-temperature transport properties of critical one-dimensional systems that can be described, at equilibrium, by a Luttinger liquid. We focus on the prototypical setting where two semi-infinite chains are prepared in two thermal states at small but different temperatures and suddenly joined together. At large distances x and times t, conformal field theory characterizes the energy transport in terms of a single light cone spreading at the sound velocity v. Energy density and current take different constant values inside the light cone, on its left, and on its right, resulting in a three-step form of the corresponding profiles as a function of ζ=x/t. Here, using a nonlinear Luttinger liquid description, we show that for generic observables this picture is spoiled as soon as a nonlinearity in the spectrum is present. In correspondence of the transition points x/t=±v, a novel universal region emerges at infinite times, whose width is proportional to the temperatures on the two sides. In this region, expectation values have a different temperature dependence and show smooth peaks as a function of ζ. We explicitly compute the universal function describing such peaks. In the specific case of interacting integrable models, our predictions are analytically recovered by the generalized hydrodynamic approach.

Glucose Sensing with Phenylboronic Acid Functionalized Hydrogel-Based Optical Diffusers.

Phenylboronic acids have emerged as synthetic receptors that can reversibly bind to cis-diols of glucose molecules. The incorporation of phenylboronic acids in hydrogels offers exclusive attributes; for example, the binding process with glucose induces Donnan osmotic pressure resulting in volumetric changes in the matrix. However, their practical applications are hindered because of complex readout approaches and their time-consuming fabrication processes. Here, we demonstrate a microimprinting method to fabricate densely packed concavities in phenylboronic acid functionalized hydrogel films. A microengineered optical diffuser structure was imprinted on a phenylboronic acid based cis-diol recognizing motif prepositioned in a hydrogel film. The diffuser structure engineered on the hydrogel was based on laser-inscribed arrays of imperfect microlenses that focused the incoming light at different focal lengths and direction resulting in a diffused profile of light in transmission and reflection readout modes. The signature of the dimensional modulation was detected in terms of changing focal lengths of the microlenses due to the volumetric expansion of the hydrogel that altered the diffusion spectra and transmitted beam profile. The transmitted optical light spread and intensity through the sensor was measured to determine variation in glucose concentrations at physiological conditions. The sensor was integrated in a contact lens and placed over an artificial eye. Artificial stimulation of variation in glucose concentration allowed quantitative measurements using a smartphone’s photodiode. A smartphone app was utilized to convert the received light intensity to quantitative glucose concentration values. The developed sensing platform offers low cost, rapid fabrication, and easy detection scheme as compared to other optical sensing counterparts. The presented detection scheme may have applications in wearable real-time biomarker monitoring devices at point-of-care settings.

Massively Multiplexed Tip-Based Photochemical Lithography under Continuous Capillary Flow

Summary Multiplexed microarrays—where different biological probes are spatially encoded onto a surface into spots with micrometer-scale diameters—have facilitated the rapid advancement of "omics" research. Further miniaturization of feature diameters could increase the number of probes in a microarray, reduce the sample required for analysis, and decrease costs. Tip-based lithography (TBL) has gained popularity for patterning delicate, biologically active materials, but no versatile TBL-based multiplexing strategy has been devised. Here, we combine microfluidics, beam pen lithography, and photochemical surface reactions to create multiplexed arrays. For proof of concept, the thiol-ene reaction was optimized, and the reaction kinetics were analyzed. Subsequently, we created several patterns containing multiple fluorescent alkenes, where each pattern was designed to demonstrate a different capability of this instrument. This patterning strategy is a powerful approach to studying and optimizing organic reactions on surfaces and creating massively multiplexed arrays and, as such, could provide an entirely new approach for miniaturizing biochips or understanding interfacial reactivity.

Light Spread Manipulation in Scintillators Using Laser Induced Optical Barriers.

We are using the Laser Induced Optical Barriers (LIOB) technique to fabricate scintillator detectors with combined performance characteristics of the two standard detector types, mechanically pixelated arrays and monolithic crystals. This is done by incorporation of so-called optical barriers that have a refractive index lower than that of the crystal bulk. Such barriers can redirect the scintillation light and allow for control of the light spread in the detector. Previous work has shown that the LIOB technique has the potential to achieve detectors with high transversal and depth of interaction (DOI) resolution simultaneously in a single-side readout configuration, suitable for high resolution PET imaging. However, all designs studied thus far present edge effect issues similarly as in the standard detector categories. In this work we take advantage of the inherent flexibility of the LIOB technique and investigate alternative barrier patterns with the aim to address this problem. Light transport simulations of barrier patterns in LYSO:Ce, with deeper barrier walls moving towards the detector edge show great promise in reducing the edge effect, however there is a trade-off in terms of achievable DOI information. Furthermore, fabrication and characterization of a 20 mm thick LYSO:Ce detector with optical barriers forming a pattern of 1 × 1 × 20mm3 pixel like structures show that light channeling in laser-processed detectors in agreement with optical barriers with refractive index between 1.2 and 1.4 is achievable.

Ultrahigh resolution radiation imaging system using an optical fiber structure scintillator plate

High resolution imaging of radiation is required for such radioisotope distribution measurements as alpha particle detection in nuclear facilities or high energy physics experiments. For this purpose, we developed an ultrahigh resolution radiation imaging system using an optical fiber structure scintillator plate. We used a ~1-μm diameter fiber structured GdAlO3:Ce (GAP) /α-Al2O3 scintillator plate to reduce the light spread. The fiber structured scintillator plate was optically coupled to a tapered optical fiber plate to magnify the image and combined with a lens-based high sensitivity CCD camera. We observed the images of alpha particles with a spatial resolution of ~25 μm. For the beta particles, the images had various shapes, and the trajectories of the electrons were clearly observed in the images. For the gamma photons, the images also had various shapes, and the trajectories of the secondary electrons were observed in some of the images. These results show that combining an optical fiber structure scintillator plate with a tapered optical fiber plate and a high sensitivity CCD camera achieved ultrahigh resolution and is a promising method to observe the images of the interactions of radiation in a scintillator.

High -spatial-resolution X-ray Inspection by Pixelated Scintillator

X-ray inspections using X-ray flat panel detectors (FPDs) have been widely used in electronic packaging to detect defects and contaminations. In the FPDs, scintillating materials convert X-ray into visible light, and a-Si photodiode array converts the light into electrons for imaging. However, it is desired that the spatial resolution of FPDs is improved because the light spreading inside scintillator causes crosstalk to next a-Si pixels and the resolution is degraded. In this study, the scintillator was pixelated with same pixel pitch as a-Si photodiode array by barrier rib structure to limit the light spreading, and the spatial resolution was improved. The pixelated scintillator was aligned with 83μm pixel pitch of a-Si photodiode array and set as a FPD. The FPD with 83μm pitch pixelated scintillator showed high modulation transfer function (mTF) such as >0.90 at 2cycles/mm. The MTF value was almost equal to the maximum value that can be theoretically achieved. Thus the FPD with pixelated scintillator has great potential to apply to high spatial-resolution X-ray inspection.

Design of DOI Detector Module for PET through the Light Spread Distribution

Design of DOI Detector Module for PET through the Light Spread Distribution

Penalized-Likelihood Reconstruction With High-Fidelity Measurement Models for High-Resolution Cone-Beam Imaging.

We present a novel reconstruction algorithm based on a general cone-beam CT forward model, which is capable of incorporating the blur and noise correlations that are exhibited in flat-panel CBCT measurement data. Specifically, the proposed model may include scintillator blur, focal-spot blur, and noise correlations due to light spread in the scintillator. The proposed algorithm (GPL-BC) uses a Gaussian Penalized-Likelihood objective function, which incorporates models of blur and correlated noise. In a simulation study, GPL-BC was able to achieve lower bias as compared with deblurring followed by FDK as well as a model-based reconstruction method without integration of measurement blur. In the same study, GPL-BC was able to achieve better line-pair reconstructions (in terms of segmented-image accuracy) as compared with deblurring followed by FDK, a model-based method without blur, and a model-based method with blur but not noise correlations. A prototype extremities quantitative cone-beam CT test-bench was used to image a physical sample of human trabecular bone. These data were used to compare reconstructions using the proposed method and model-based methods without blur and/or correlation to a registered CT image of the same bone sample. The GPL-BC reconstructions resulted in more accurate trabecular bone segmentation. Multiple trabecular bone metrics, including trabecular thickness (Tb.Th.) were computed for each reconstruction approach as well as the CT volume. The GPL-BC reconstruction provided the most accurate Tb.Th. measurement, 0.255 mm, as compared with the CT derived value of 0.193 mm, followed by the GPL-B reconstruction, the GPL-I reconstruction, and then the FDK reconstruction (0.271 mm, 0.309 mm, and 0.335 mm, respectively).