Light Dispersion Research Articles

Experimental study of a depth-encoding PET detector inserting horizontal-striped glass between crystal layers

A depth-encoding positron emission tomography (PET) detector inserting a horizontal-striped glass between pixilated scintillation crystal layers was developed and experimentally evaluated. The detector consists of 2-layers of 4×4 LYSO array arranged with a 3.37 mm pitch. Horizontal-striped glasses with 1×4 array with different thickness of 3, 4 and 5 mm were inserted between top- and bottom-crystal layers. Bottom surface of bottom-layer was optically coupled to a 4×4 GAPD array. Sixteen output signals from DOI-PET detector were multiplexed by modified resistive charge division (RCD) networks and multiplexed signals were fed into custom-made charge-sensitive preamplifiers. The four amplified signals were digitized and recorded by the custom-made DAQ system based on FPGA. The four digitized outputs were post-processed and converted to flood histograms for each interaction event. Experimental results revealed that all crystal pixels were clearly identified on the 2D flood histogram without overlapping. Patterns of the 2D flood histogram were constituted with arrangements of [bottom–top–bottom–top–\\ldots–top–bottom–top–bottom] crystal responses in X-direction. These could be achieved by employing horizontal-striped glass that controlled the extent of light dispersion towards the X-direction in crystal layers for generation of a different position mapping for each layer and the modified RCD network that controls degree of charge sharing in readout electronics for reduction of identification error. This study demonstrated the proposed DOI-PET detector can extract the 3D γ-ray interaction position without considerable performance degradation of PET detector from the 2D flood histogram.

A broadband achromatic metalens for focusing and imaging in the visible.

A key goal of metalens research is to achieve wavefront shaping of light using optical elements with thicknesses on the order of the wavelength. Such miniaturization is expected to lead to compact, nanoscale optical devices with applications in cameras, lighting, displays and wearable optics. However, retaining functionality while reducing device size has proven particularly challenging. For example, so far there has been no demonstration of broadband achromatic metalenses covering the entire visible spectrum. Here, we show that by judicious design of nanofins on a surface, it is possible to simultaneously control the phase, group delay and group delay dispersion of light, thereby achieving a transmissive achromatic metalens with large bandwidth. We demonstrate diffraction-limited achromatic focusing and achromatic imaging from 470 to 670 nm. Our metalens comprises only a single layer of nanostructures whose thickness is on the order of the wavelength, and does not involve spatial multiplexing or cascading. While this initial design (numerical aperture of 0.2) has an efficiency of about 20% at 500 nm, we discuss ways in which our approach may be further optimized to meet the demand of future applications.

A Further Test of Lorentz Violation from the Rest-frame Spectral Lags of Gamma-Ray Bursts

Abstract Lorentz invariance violation (LIV) can manifest itself by an energy-dependent vacuum dispersion of light, which leads to arrival time differences of photons with different energies originating from the same astronomical source. The spectral lags of gamma-ray bursts (GRBs) have been widely used to investigate the possible LIV effect. However, all current investigations used lags extracted in the observer frame only. In this work, we present, for the first time, an analysis of the LIV effect and its redshift dependence in the cosmological rest frame. Using a sample of 56 GRBs with known redshifts, we obtain a robust limit on LIV by fitting their rest-frame spectral lag data using both a maximization of the likelihood function and a minimum χ 2 statistic. Our analysis indicates that there is no evidence of LIV. Additionally, we test the LIV in different redshift ranges by dividing the full sample into four redshift bins. We also find no evidence for the redshift variation of the LIV effect.

Absorption and dispersion management of near-infrared probe light in the carbon nanotube quantum dot nanostructure with spin–orbit coupling

We investigated the absorption–dispersion properties of near-infrared probe light in the carbon nanotube quantum dot (CNT-QD) nanostructure with spin–orbit (SO) coupling parameter based on quantum mechanical density matrix formalisms. We found that in the presence of SO parameter, the amplification of probe light can be achieved in the presence and lack of population inversion (lasing with and without inversion). Moreover, we realized that the normal and anomalous dispersion of probe light can occur by redacting the incoherent pumping and transverse magnetic fields.

EFECTO DE BIOCOMPOSITOS DE QUITOSANO-ACEITE ESENCIAL DE PIRUL (Schinus molle) SOBRE LA CINÉTICA DE CRECIMIENTO, VIABILIDAD E INTEGRIDAD DE LA MEMBRANA DE Colletotrichum gloeosporioides

Recent studies have demonstrated that the micro and nanoparticles of chitosan (CS) have an in vitro antifungal effect against filamentous fungus that are of importance in food. This study was made to evaluate the antifungal activity of chitosan nanoparticles, pepper tree essential oil (PEO), and chitosan biocomposites loaded with pepper tree essential oil (CS-PEO), on the in vitro growth of Colletotrichum gloeosporioides. The particles were obtained by nanoprecipitation and the size and superficial charge (Z potential) were evaluated using dynamic light dispersion analysis (DLS). The mutagenic potential and the acute toxicity were also evaluated. The effect on the radial growth, spore’s germination, viability, and damage to the membrane´s integrity, were determined. The effect on the kinetic growth parameters was also determined. Results showed that the CS and CS-PEO particles diameter was 341.2 ± 12.40 and 355.3 ± 25.3 mm, respectively. In vitro assays showed both nanoparticles with a high inhibition potential on C. gloeosporioides, and low mutagenicity and toxicity. At a concentration of 0.160 mg/mL, the CS-PEO biocomposite presented a greater (P<0.05) inhibitory effect on radial growth, spore germination and viability of the spores, this constitute a natural alternative to the use of fungicidal chemical agents for fungus control.

Interaction of pulsed laser radiation with a polycarbonate-based composite

Abstract—The interaction of pulsed laser radiation with foil-clad polycarbonate containing diffraction gratings is studied. It is found that the laser beam reflected from diffraction gratings is selffocused in polycarbonate bulk and becomes a seed for changing the polycarbonate structure, which leads to the glass transition and growth of ordered structures with symmetry features, which gives rise to the light dispersion effect in composites. A probable formation mechanism of ordered structures in polycarbonate during irradiation is proposed.

Error compensation in NC machine tools

This work contributes to the development of new approaches to tolerancing for machining using a machine tool with digital control. Our research is focused in two directions. First, it focuses on the manufacturing tolerances. The aim was to establish procedures for validating ranges of light manufacturing dispersions, manufacturing errors and machine tools with digital control, and cover various types of critical tolerances targeted. The second deals with design tolerances, for which we proposed a method for calculating functional tolerances.&#x0D; Keywords: Errors, tolerance, manufacturing.

Laboratory-scale photobiotechnology-current trends and future perspectives.

Phototrophic bioprocesses are a promising puzzle piece in future bioeconomy concepts but yet mostly fail for economic reasons. Besides other aspects, this is mainly attributed to the omnipresent issue of optimal light supply impeding scale-up and -down of phototrophic processes according to classic established concepts. This MiniReview examines two current trends in photobiotechnology, namely microscale cultivation and modeling and simulation. Microphotobioreactors are a valuable and promising trend with microfluidic chips and microtiter plates as predominant design concepts. Providing idealized conditions, chip systems are preferably to be used for acquiring physiological data of microalgae while microtiter plate systems are more appropriate for process parameter and medium screenings. However, these systems are far from series technology and significant improvements especially regarding flexible light supply remain crucial. Whereas microscale is less addressed by modeling and simulation so far, benchtop photobioreactor design and operation have successfully been studied using such tools. This particularly includes quantitative model-assisted understanding of mixing, mass transfer, light dispersion and particle tracing as well as their relevance for microalgal performance. The ultimate goal will be to combine physiological data from microphotobioreactors with hybrid models to integrate metabolism and reactor simulation in order to facilitate knowledge-based scale transfer of phototrophic bioprocesses.

Controllable hierarchical micro/nano patterns on biomaterial surfaces fabricated by ultrasonic nanocrystalline surface modification

In this work, we have shown that Ultrasonic Nanocrystal Surface Modification (UNSM) cannot only improve the mechanical properties of Ti-based biomaterials but also produce surface texture with hierarchical micro/nanoscale patterns due to its high controllability. After UNSM-treatment the surface texture of Ti-based biomaterial consists of a major microscale structure with widths ranging from 4μm to 200μm, and an embedded nanoscale structure with widths as small as 120nm. With a customized cylinder tip, the average surface roughness (Ra) can be reduced to 0.03μm, comparable to the superfinishing surface. The embedded nanoscale structure originates from the formation of the pile-up, which is determined by the elastic-plastic property of materials. Such hierarchical patterns enable new functions for the treated surface. It is demonstrated that light dispersion and the alteration of wettability can be achieved by controlling surface patterns using UNSM. The capacity of improving mechanical properties, biocompatibility, and hydrophobicity simultaneously, in conjunction with its low-cost and easy-to-operate features, makes it a promising surface engineering technique for biomaterial treatment.

Quantum gravity without vacuum dispersion

A generic prediction of quantum gravity is the vacuum dispersion of light, and hence that a photon’s speed depends on its energy. We present further numerical evidence for a scale-dependent speed of light in the causal dynamical triangulation (CDT) approach to quantum gravity. We show that the observed scale-dependent speed of light in CDT can be accounted for by a scale-dependent transformation of geodesic distance, whose specific functional form implies a discrete equidistant area spectrum. We make two nontrivial tests of the proposed scale transformation: a comparison with the leading-order quantum correction to the gravitational potential and a comparison with the generalized uncertainty principle. In both cases, we obtain the same functional form. However, contrary to the widespread prediction of vacuum dispersion in quantum gravity, numerous experiments have now definitively ruled out linear vacuum dispersion beyond Planckian energy scales [Formula: see text], and have even constrained quadratic dispersion at the level [Formula: see text]. Motivated by these experimental constraints, we seek to reconcile quantum gravity with the absence of vacuum dispersion. We point out that given a scale-dependent geodesic distance, a scale-dependent time interval becomes essential to maintaining an invariant speed of light. We show how a particular scale-dependent time interval allows a photon’s speed to remain independent of its energy.

Students’ interpretations and reasoning about phenomena with negative rates of change throughout a model development sequence

In this article, we examine how a sequence of modeling activities supported the development of students’ interpretations and reasoning about phenomena with negative average rates of change in different physical phenomena. Research has shown that creating and interpreting models of changing physical phenomena is difficult, even for university level students. Furthermore, students’ reasoning about models of phenomena with negative rates of change has received little attention in the research literature. In this study, 35 students preparing to study engineering participated in a 6-week instructional unit on average rate of change that used a sequence of modeling activities. Using an analysis of the students’ work, our results show that the sequence of modeling activities was effective for nearly all students in reasoning about motion with negative rates along a straight path. Almost all students were successful in constructing graphs of changing phenomena and their associated rate graphs in the contexts of motion, light dispersion and a discharging capacitor. Some students encountered new difficulties in interpreting and reasoning with negative rates in the contexts of light dispersion, and new graphical representations emerged in students’ work in the context of the discharging capacitor with its underlying exponential structure. The results suggest that sequences of modeling activities offer a structured approach for the instruction of advanced mathematical content.

Combining \u03b5-Near-Zero Behavior and Stopped Light Energy Bands for Ultra-Low Reflection and Reduced Dispersion of Slow Light

We investigate media which exhibits epsilon-near-zero (ENZ) behavior while simultaneously sustaining stopped light energy bands which contain multiple points of zero group velocity (ZGV). This allows the merging of state-of-the-art phenomena that was hitherto attainable in media that demonstrated these traits separately. Specifically, we demonstrate the existence of Ferrell-Berreman (FB) modes within frequency bands bounded by points of ZGV with the goal to improve the coupling efficiency and localization of light in the media. The FB mode is formed within a double layer, thin-film stack where at subwavelength thicknesses the structure exhibits a very low reflection due to ENZ behavior. In addition, the structure is engineered to promote a flattened frequency dispersion with a negative permittivity able to induce multiple points of ZGV. For proof-of-concept, we propose an oxide-semiconductor-oxide-insulator stack and discuss the useful optical properties that arise from combining both phenomena. A transfer matrix (TM) treatment is used to derive the reflectivity profile and dispersion curves. Results show the ability to reduce reflection below 0.05% in accordance with recent experimental data while simultaneously exciting a polariton mode exhibiting both reduced group velocity and group velocity dispersion (GVD).

Birefringent light propagation on anisotropic cosmological backgrounds

Exact electromagnetic wave solutions to Maxwell equations on anisotropic Bianchi I cosmological spacetime backgrounds are studied. The waves evolving on Bianchi I spacetimes exhibit birefringence (associated to linear polarization) and dispersion. The particular case of a vacuum--dominated anisotropic Universe, which reproduces a Friedmann-Robertson-Walker Universe (for late times) while for earlier times it matches a Kasner Universe, is studied. The electromagnetic waves do not, in general, follow null geodesics. This produces a modification of the cosmological redshift, which is now dependent on light polarization and dispersion and its non-null geodesic behavior. New results presented here may help to tackle some issues related to the "horizon" problem.

Rethinking aqueous phase diffusion related isotope fractionation: Contrasting theoretical effects with observations at the field scale

Aqueous phase diffusion-related isotope fractionation (DRIF) was investigated through modelling to determine under what subsurface conditions carbon isotope DRIF effects would be observable using typical sampling approaches. A dispersive enrichment factor was defined based on heavy and light isotopologue dispersion coefficients. For a given ratio of source concentration (C0) to method detection limit (MDL), the maximum DRIF in a system increased linearly with transverse dispersive enrichment factor. Using this linear relationship, the critical dispersion enrichment factor for which DRIF would not be observable was quantified. Dispersive enrichment factors for various contaminants (benzene, toluene, chlorinated compounds) were estimated using field scale transverse dispersion coefficients upscaled from compound specific or non-compound specific local scale dispersivity. All predicted dispersive enrichment factors with non-compound specific dispersivity are smaller than critical values even for high C0/MDL ratios (e.g. 25,000), indicating DRIF would generally not be observable in systems where soil dispersivity is non-compound specific. To date, this finding has not been clearly articulated in the DRIF literature. While the calculated dispersive enrichment factors for some compounds with compound specific transverse dispersivity exceeded the critical values at which DRIF might become significant, the zones in which DRIF could potentially be observable were limited to bands below 0.5m wide on lateral plume edges. In aquifer-aquitard systems, DRIF was theoretically detectable only in thin aquifers (e.g. 0.5m) bounded by thick (e.g. meters) aquitards. DRIF due to back diffusion from aquitards would not be observable regardless of aquifer thickness. Simulations addressing the mixing effect in wells demonstrated that DRIF effects would be difficult to identify in the field without a sampling strategy (including smaller than industry norm well screen lengths, and fine sampling scales) expressly targeted towards that goal. The results of this study help identify what the required characteristics of such a field strategy might be.

Electrochemical synthesis of CuSCN nanostructures, tuning the morphological and structural characteristics: From nanorods to nanostructured layers

P-type CuSCN nanorods (NRs) grown on CuSCN seed layers were obtained with modulated diameters through an electrochemical procedure. Their morphological, structural, optical, electrochemical and photoelectrochemical features were studied in depth. Morphology of samples can be tuned from a near vertically and dense 1D nanostructure to a quasi 2D film according the value of the SCN– /Cu2+ molar ratio (r) present in the electrochemical bath. Raman studies confirmed the nature of CuSCN in its beta phase. For low r values CuSCN NRs presented high preferential orientation along the c-axis and high optical scattering at low wavelengths which lead to both low haze and high integrated diffuse reflectance. Band gap values were also affected by the r value thus experiencing a redshift, probably related to both quantum confinement and light dispersion. Electrochemical and photoelectrochemical measurements confirmed the p-type behavior of samples together with the enhancement of their surface at low r values. This knowledge opens new and more objective perspectives in the real use of CuSCN nanostructures in photovoltaics.

Constraining Anisotropic Lorentz Violation via the Spectral-lag Transition of GRB 160625B

Abstract Violations of Lorentz invariance can lead to an energy-dependent vacuum dispersion of light, which results in arrival-time differences of photons with different energies arising from a given transient source. In this work, direction-dependent dispersion constraints are obtained on nonbirefringent Lorentz-violating effects using the observed spectral lags of the gamma-ray burst GRB 160625B. This burst has unusually large high-energy photon statistics, so we can obtain constraints from the true spectral time lags of bunches of high-energy photons rather than from the rough time lag of a single highest-energy photon. Also, GRB 160625B is the only burst to date having a well-defined transition from positive lags to negative lags, providing a unique opportunity to distinguish Lorentz-violating effects from any source-intrinsic time lag in the emission of photons of different energy bands. Our results place comparatively robust two-sided constraints on a variety of isotropic and anisotropic coefficients for Lorentz violation, including the first bounds on Lorentz-violating effects from operators of mass dimension 10 in the photon sector.

Design of vacuum ultraviolet spectroscopy system on J-TEXT

A Vacuum Ultraviolet (VUV) spectroscopy system is designed on J-TEXT tokamak in order to study the transport of the light impurities including carbon and oxygen in edge region with the effect of RMP or ECRH. It covers the wavelength ranging from 30 to 300nm. The normal incidence monochromator with concave grating with the focal length of 1 meter is chosen for light dispersion. A 1024*1024 pixels back illuminated charge-coupled device (CCD) is chosen as the detector for the profile measurement. The observing region is from 1.1a (minor radius) at the lower part of the plasma to 0.6a at the upper part with an adjusting spatial resolution slit. In order to prove the potential for the expected signal intensity, spectra are simulated using the impurity transport code STRAHL. The photons numbers of C II 133.45nm, C III 97.7nm and C IV 154.9nm in J-TEXT plasma are estimated to evaluate the practicability of the system. The wavelength calibration will be achieved using the light from plasma in tokamak at different discharge conditions. The branching ratio technique and bremsstrahlung are combined for the absolute intensity calibration.

Temporal focusing-based widefield multiphoton microscopy with spatially modulated illumination for biotissue imaging.

A developed temporal focusing-based multiphoton excitation microscope (TFMPEM) has a digital micromirror device (DMD) which is adopted not only as a blazed grating for light spatial dispersion but also for patterned illumination simultaneously. Herein, the TFMPEM has been extended to implement spatially modulated illumination at structured frequency and orientation to increase the beam coverage at the back-focal aperture of the objective lens. The axial excitation confinement (AEC) of TFMPEM can be condensed from 3.0 μm to 1.5 μm for a 50 % improvement. By using the TFMPEM with HiLo technique as two structured illuminations at the same spatial frequency but different orientation, reconstructed biotissue images according to the condensed AEC structured illumination are shown obviously superior in contrast and better scattering suppression. Picture: TPEF images of the eosin-stained mouse cerebellar cortex by conventional TFMPEM (left), and the TFMPEM with HiLo technique as 1.09 μm-1 spatially modulated illumination at 90° (center) and 0° (right) orientations.

Rat superior colliculus neurons respond to large visual stimuli flashed outside the classical receptive field.

Spatial integration of visual stimuli is a crucial step in visual information processing yet it is often unclear where this integration takes place in the visual system. In the superficial layers of the superior colliculus that form an early stage in visual information processing, neurons are known to have relatively small visual receptive fields, suggesting limited spatial integration. Here it is shown that at least for rats this conclusion may be wrong. Extracellular recordings in urethane-anaesthetized young adult rats (1.5–2 months old) showed that large stimuli of over 10° could evoke detectable responses well outside the borders of ‘classical’ receptive fields determined by employing 2° – 3.5° stimuli. The presence of responses to large stimuli well outside these ‘classical’ receptive fields could not be explained neither by partial overlap between the visual stimulus and the receptive field, nor by reflections or light dispersion from the stimulation site. However, very low frequency (<0.1 Hz) residual responses to small stimuli presented outside the receptive field may explain the obtained results if we assume that the frequency of action potentials during a response to a stimulus outside RF is proportional to the stimulus area. Thus, responses to large stimuli outside RF may be predicted by scaling according to the stimulus area of the responses to small stimuli. These data demonstrate that neurons in the superficial layers of the superior colliculus are capable of integrating visual stimuli over much larger area than it can be deduced from the classical receptive field.

Probing gas-to-particle transition in a moderately sooting atmospheric pressure ethylene/air laminar premixed flame. Part I: gas phase and soot ensemble characterization

A comprehensive investigation was conducted on a sooting ethylene laminar premixed flame: the present contribution focuses on the characterization of the gas composition by gas microsampling and GC/MS analysis, and of soot properties by optical measurements; Part II presents detailed measurements of soot nucleation by thermophoretic sampling and differential mobility analysis. Stable species up to 3-ring aromatics were quantified and compared with a computational model using two distinct chemistry models and accounting for buoyancy. Disagreement with respect to critical soot precursors was found, whose concentrations were typically overestimated by one order of magnitude in the models. Reliable thermocouple measurements of temperature, when matched by multi-color pyrometry results, provided information on soot volume fractions and optical properties complementing laser light extinction measurements. Results evidenced a sharp increase of the soot volume fraction in the inception zone of the flame followed by a plateauing behavior, similar to the trend of aromatic species, which is consistent with the well-known link between aromatic growth kinetics and soot inception. In addition, fit of pyrometric soot temperature to gas phase thermocouple measurements provided information on the light absorption dispersion exponent, revealing the aging of soot from near transparency in the visible spectral range for young soot particles to a more graphitic-like material further downstream. The presence of the stagnation plate used to stabilize the flame induced a sharp increase in the soot volume fraction and its dispersion exponent in the thermal boundary layer of the plate. This evidence suggests the occurrence of condensation of semi-volatile material under the cooling of flame products occurring near the plate, whose origin is yet to be firmly established but may be mediated by flame ions.