Light Collection Research Articles

A method to characterize metalenses for light collection applications

Metalenses and metasurfaces are promising emerging technologies that could improve light collection in light collection detectors, concentrating light on small area photodetectors such as silicon photomultipliers. Here we present a detailed method to characterize metalenses to assess their efficiency at concentrating monochromatic light coming from a wide range of incidence angles, not taking into account their imaging quality.

Sparse SiPM Pixel Arrangement for a TOF-PET Detector Design that Achieves 100 ps Coincidence Time Resolution

Coupling silicon photomultipliers (SiPMs) to the side of a long and narrow scintillation crystal elements offers near-complete light extraction efficiency, independent of 511 keV photon interaction depth, and reduced scintillation light transit time jitter in its path toward the photodetector. With these advantages, significant improvements in PET detector coincidence time resolution (CTR) can be achieved compared to the traditional scintillation light readout configuration where an SiPM is coupled on the narrow end of crystals. Moreover, the arrangement of photosensors along the crystal’s side intrinsically provides a three-dimensional position sensing detector. One consideration for the side readout approach is the increase in the number of SiPMs required to read each crystal element. In this work, we investigate the achievable CTR when the number of SiPM elements coupled to the side of crystals is parametrically varied, including different crystal lengths and reflector configurations. A simulation model for CTR was validated against measurements with 3-20 mm length crystals employing side readout of scintillation light. The validated simulation model was used to parametrically investigate twenty-seven configurations of SiPMs arranged along the side of crystal elements. Reflector and sensor placement was parametrically varied to find configurations that optimize light collection efficiency, energy resolution, and CTR. One configuration achieved 101±1 ps FWHM CTR, while maintaining high light collection efficiency and good energy performance with a 33% reduction in photosensor area.

Additive GaN Solid Immersion Lenses for Enhanced Photon Extraction Efficiency from Diamond Color Centers.

Effective light extraction from optically active solid-state spin centers inside high-index semiconductor host crystals is an important factor in integrating these pseudo-atomic centers in wider quantum systems. Here, we report increased fluorescent light collection efficiency from laser-written nitrogen-vacancy (NV) centers in bulk diamond facilitated by micro-transfer printed GaN solid immersion lenses. Both laser-writing of NV centers and transfer printing of micro-lens structures are compatible with high spatial resolution, enabling deterministic fabrication routes toward future scalable systems development. The micro-lenses are integrated in a noninvasive manner, as they are added on top of the unstructured diamond surface and bonded by van der Waals forces. For emitters at 5 μm depth, we find approximately 2× improvement of fluorescent light collection using an air objective with a numerical aperture of NA = 0.95 in good agreement with simulations. Similarly, the solid immersion lenses strongly enhance light collection when using an objective with NA = 0.5, significantly improving the signal-to-noise ratio of the NV center emission while maintaining the NV's quantum properties after integration.

Calibration method of crosshair light sharing PET detector with TOF and DOI capabilities

Objective. A crosshair light sharing (CLS) PET detector as a TOF-DOI PET detector with high spatial resolution has been developed. To extend that work, a detector calibration method was developed to achieve both higher coincidence resolving time (CRT) and DOI resolution. Approach. The CLS PET detector uses a three-layer reflective material in a two-dimensional crystal array to form a loop structure within a pair of crystals, enabling a CRT of about 300 ps and acquisition of DOI from multi-pixel photon counter (MPPC) output ratios. The crystals were 1.45 × 1.45 × 15 mm3 fast LGSO, and the crystal array was optically coupled to an MPPC array. It is important to reduce as many inter-crystal scattering (ICS) events as possible in advance for the accurate detector calibration. DOI information is also expected to improve the CRT because it can estimate the time delay due to the detection depth of crystals. Main results. Using crystal identification and light collection rate of the highest MPPC output reduces the number of ICS events, and CRT is improved by 26%. In addition, CRT is further improved by 13% with a linear correction of time delay as a function of energy. The DOI is ideally estimated from the output ratio of only the MPPC pairs optically coupled to the interacted crystals, which is highly accurate, but the error is large due to light leakage in actual use. The previous method, which also utilizes light leakage to calculate the output ratio, is less accurate, but the error can be reduced. Using the average of the two methods, it is possible to improve the DOI resolution by 12% while maintaining the smaller error. Significance. By applying the developed calibration method, the CLS PET detector achieves the CRT of 251 ps and the DOI resolution of 3.3 mm.

Beam test, simulation, and performance evaluation of PbF2 and PWO-UF crystals with SiPM readout for a semi-homogeneous calorimeter prototype with longitudinal segmentation

Crilin (Crystal Calorimeter with Longitudinal Information) is a semi-homogeneous, longitudinally segmented electromagnetic calorimeter based on high-Z, ultra-fast crystals with UV-extended SiPM readout. The Crilin design has been proposed as a candidate solution for both a future Muon Collider barrel ECAL and for the Small Angle Calorimeter of the HIKE experiment. As a part of the Crilin development program, we have carried out beam tests of small (10 × 10 × 40 mm3) lead fluoride (PbF2) and ultra-fast lead tungstate (PbWO4, PWO-UF) crystals with 120 GeV electrons at the CERN SPS to study the light yield, timing response, and systematics of light collection with a proposed readout scheme. For a single crystal of PbF2, corresponding to a single Crilin cell, a time resolution of better than 25 ps is obtained for>3 GeV of deposited energy. For a single cell of PWO-UF, a time resolution of better than 45 ps is obtained for the same range of deposited energy. This timing performance fully satisfies the design requirements for the Muon Collider and HIKE experiments. Further optimizations of the readout scheme and crystal surface preparation are expected to bring further improvements.

Bio-templated energy transfer system for constructing artificial light-harvesting antennae, white light generation, and photonic nanowires

Developing environmentally friendly, sustainable, and biocompatible artificial light-harvesting systems has become an essential area of research to understand natural light-harvesting processes involving multistep resonance energy transfer and building efficient energy conversion systems related to energy and optoelectronic applications. In this direction, bio-scaffolded artificial energy transfer systems for panchromatic light collection and sequential energy transfer have fascinated the scientific community. In this review, we have discussed what the dynamic structure and intrinsic physical properties of biomolecules like deoxyribonucleic acid, proteins, and peptides can provide for the development of new optical devices, sustainable and environmentally friendly white emitting materials, and cascaded energy transfer systems for energy harvesting from light. In doing so, we have highlighted some of the recent advances in bio-scaffolds as a platform for the assembly of different types of donor–acceptor chromophores involved in fluorescence energy transfer.

The JUNO water Cherenkov detector system

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20 kton liquid scintillator detector with the primary physics goal of the neutrino mass ordering determination. The detector will be built in a laboratory 650-m underground. The pool is filled with 34 kton ultrapure water outside the central detector as a water Cherenkov detector for cosmic muon detection. 2400 MCP-PMTs detect the water Cherenkov light produced by cosmic muons. The inner surface of the water veto is covered with a Tyvek reflector to increase the light collection efficiency. A water system is used for water purification and circulation to maintain high water quality for optimal detector performance. A set of radon removal equipment will be integrated with the water system to reduce the radon-induced background in the central detector. Based on prototype studies, the radon concentration in water could be reduced to less than 10 mBq/m3. The cosmic muon detection efficiency of the water Cherenkov detector can reach 99.5%. With this veto system, the cosmic muon-induced fast neutron background can also be reduced to the level of about ∼0.1/day level.

Sunflower‐Inspired Light‐Tracking System and Spatial Encryption Imaging based on Linear Flexible Perovskite Photodetector Arrays

AbstractLight‐tracking systems and wide‐angle imaging are garnering increasing interest in the field of artificial intelligence due to their benefits to improve the light collection efficiency. Perovskite photodetectors have become the mainstream choice for their high adsorption coefficient, flex‐compatible properties, and low‐cost solution process. However, the fabrication of precise angle‐sensitive flexible detectors remains challenging due to the uncontrollable deposition of photosensitive layers. Herein, wide‐angle‐sensitive linear flexible perovskite photodetector arrays are successfully fabricated. The device exhibits a broad range of 144°, high‐resolution of 2.8°, and long‐term stability of 3000 cycles. As a proof‐of‐concept demonstration, a sunflower‐inspired light‐tracking system with adaptive following performance is illustrated. Furthermore, spatially encrypted imaging is achieved using linear perovskite photodetector arrays coupled with algorithms. This work confirms the superiority of flexible perovskite photodetectors in angle‐sensing and encryption imaging.

Recyclable MXene-bridged Z-scheme NiFe2O4/MXene/Bi2WO6 heterojunction with enhanced charge separation for efficient sonocatalytic removal of ciprofloxacin

Sonocatalysis has emerged as a promising technology for addressing environmental pollution issues. However, the efficacy of sonocatalytic processes is primarily hindered by challenges related to the sluggish flow rate of photogenerated electrons. This study presents a novel approach to address this issue by developing an improved Z-scheme NiFe2O4/MXene/Bi2WO6 (NMB) composite that exhibits exceptional sonocatalytic activity for ciprofloxacin (CIP) degradation. In particular, the NiFe2O4/MXene (5 wt%)/Bi2WO6 composite could achieve high CIP (at 10 mg/L) degradation efficiency (97.39 %) after 60 min of ultrasonic irradiation. The exceptional sonocatalytic activity of the composite was attributed to the synergistic interaction of the Z-scheme heterojunction charge transfer route and the electron mediator of Ti3C2-MXene, which enhances light collection capacity, separates photogenerated carriers efficiently, and improves redox activity of the composite. The scavenging experiments reveal that the sonocatalytic degradation of CIP was driven by holes (h+), hydroxyl radicals (•OH), and superoxide anion radicals (•O2−), with the former playing a dominant role. The results of reuse experiments demonstrate the outstanding sonocatalytic stability of the catalyst, as well as its uncomplicated recovery. The developed NMB Z-scheme composite shows promise for sonocatalytic treatment of antibiotics in industrial wastewaters, particularly those with high turbidity and/or low transparency. The findings also open up avenues for developing efficient and cost-effective sonocatalysts with good recyclability and remarkable performance.

Laser direct writing based flexible solar energy harvester

With the rapid advancement of flexible electronics, conventional rigid batteries, which serve as energy devices for flexible electronics, are no longer capable of meeting developmental requirements. In this context, solar cells, as an eco-friendly, low-carbon, and sustainable energy technology, have gained significant recognition. This paper aims to design a flexible solar energy harvester (FSEH) based on laser direct writing. The FSEH is comprised of commercial PET/PI films, flexible Cu circuits, and amorphous silicon solar cells which provide excellent flexibility and sustainability. The FSEH was formed by soldering the solar collection array to the laser direct-written flexible Cu circuit by using solder paste. The solar energy harvesting array consists of six sets of series-connected amorphous silicon solar cell arrays, with each set comprised of six amorphous silicon solar cells connected in parallel. It has a maximum light collection area of about 2772 mm2. The designed FSEH could generate energy by harvesting light energy from lights or solar radiation. The FSEH outputs 0.437 mW at the light intensity of 3000 Lux and 1.813 mW at the light intensity of 10,000 Lux. The FSEH maintains an output efficiency of over 92% with a bending angle of less than 45°. Based on laser direct writing technology which enables efficient, convenient, and large-scale production of FSEH, the FSEH is expected to form a flexible self-powered system with flexible supercapacitors and wearable electronics, and FSEH offers great advantages for the sustainable development of wearable electronics and flexible sensors.

Morphology‐Directed Light Emission from Fluorescent Janus Colloids for Programmable Chemical‐To‐Optical Signal Transduction

AbstractMaterials capable of dynamically and reversibly altering their emission are relevant for numerous optical applications. Here, the anisotropic morphology‐directed light emission from fluorescent Janus emulsion droplets, an intrinsically chemo‐responsive material platform, is investigated. Informed by experimental observations of morphology‐dependent optical confinement of internally emitted light within the higher refractive index phases, ray‐tracing is used to predict and fine‐tune the droplets’ optical properties and their ability to concentrate light. Theoretical prediction and closely matching experimental results show that the collection of incident light and the confinement of emitted light in the internal droplet phase due to total internal reflection both contribute to the droplets’ anisotropic light emission profile. A novel ratiometric dual‐angle fluorescence detection approach that exploits the gravitational alignment of the droplets is implemented to quantify the morphology‐dependent large‐scale chemically‐induced modulation of the anisotropic emission of droplet layers. Relevant emulsion design parameters are systematically examined to enhance the signal‐to‐noise ratio, and a second emitter is co‐compartmentalized inside the droplets to amplify the anisotropic light confinement via an absorption–emission cascade. Preferential excitation of dyes in proximity to the internal droplet interface enhances the collected light intensity, demonstrating that dye‐loaded Janus emulsion droplets function as stimuli‐responsive, tunable, fluorescent optical elements.

Weldable and electrochemically stable composite of graphene and polyvinylidene fluoride as a current collector for promoting reversible lithium plating/stripping

Cu foils are physically heavy and chemically inappropriate for lithium metal rechargeable batteries with lithium-metal-free negatrode (LMFRBs). Physically light carbon-based current collectors (CBCCs) with high conductivity and strong resistance toward corrosion by air or electrolyte can replace Cu foil as a preferable deposition substrate for Li. However, welding problems, lithiation or electrolyte penetration-induced mechanical strength reduction, and lithiophobility-induced fragile SEI largely limit the application of CBCCs. In this work, we prepare lightweight graphene/polyvinylidene fluoride (PVDF) composite sheet via a coating and etching process to address the above issues. Cu tabs are bonded firmly to this CBCC with acceptable resistance, guaranteeing practical application. Tightly stacked graphene nanosheets mitigate lithiation and extra Li consumption (SEI), while PVDF as the binder reinforces the mechanical strength of CBCC by hindering the electrolyte penetration. Therefore, this composite CBCC satisfies the basic requirements i.e., sufficient conductivity and mechanical strength, and viable tab welding, needed for pouch cell application. In addition, as a film-forming polymer with a low Fermi level, PVDF helps form Li–F-rich and highly insulating SEI and suppresses electron transfer to the electrolyte, which induces uniform Li+ flux and alleviates electrolyte decomposition. The stable interface and robust SEI give rise to uniform and more reversible Li plating/stripping. The assembled LMFRB using this composite CBCC achieves remarkable capacity retention of 80% after ∼50 cycles with a high plating capacity of 4 mAh cm−2.

Preparation of a beam emission spectroscopy diagnostic based on a Lyman-alpha line to diagnose core and edge-plasma density fluctuation on the HL-2A tokamak

In this article, the design of a Lyman-alpha-based beam emission spectroscopy (LAB) diagnostic on the HL-2A tokamak has been proposed for the first time. The purpose of this novel diagnostic is to measure density fluctuations of tokamak plasma. The light-collection system of LAB, which consists of the first mirror and two groups of coaxial double-mirror telescopes, can realize a two-segmented viewing field of ρ = 0‒0.2 and ρ = 0.75‒1, which is optimized to measure plasma density fluctuation, not only in the edge transport barrier region but also in the internal transport barrier region, to investigate the underlying physics of turbulence in tokamaks. Spectrometers are developed to separate out the Doppler-shifted target line (122.03 and 122.17 nm) from the background Lyman-alpha line (121.53 nm). Here, 30 Core-LAB channels and 30 Edge-LAB channels are under development on the HL-2A tokamak. It has high radial spatial resolutions of about 2.7 mm and 3.3 mm for the core and edge channels, respectively. Taking the high light intensity of this Lyman-alpha line into account, temporal resolution of 200 kHz can be ensured by broad bandwidth amplifiers. This high spatio-temporal resolution makes LAB a potential keen tool to experimentally investigate tokamak plasma physics.

Efficient photocatalytic hydrogen production by space separation of photo-generated charges from S-scheme ZnIn2S4/ZnO heterojunction

ZnIn2S4/ZnO heterostructures have been achieved by a simple in-situ growth solvothermal method. Under full spectrum irradiation, the optimal photocatalyst 2ZnIn2S4/ZnO exhibits H2 evolution rate of 13,638 (water/ethanol = 1:1) and 3036 (water) μmol·g−1h−1, which is respectively 4 and 5 times higher than that of pure ZnIn2S4. In situ illumination X-ray photoelectron spectroscopy (ISI-XPS) analysis and density functional theory (DFT) calculations show that the electrons of ZnIn2S4 are removed to ZnO through hybridization and form an internal electric field between ZnIn2S4 and ZnO. The optical properties of the catalyst and the effect of internal electric field (IEF) can increase photo-generated electrons (e−)–holes (h+) transport rate and enhance light collection, resulting in profitable photocatalytic properties. The photoelectrochemical and EPR results show that a stepped (S-scheme) heterojunction is formed in the ZnIn2S4/ZnO redox center, which greatly promotes separation of e−–h+ pairs and efficient H2 evolution. This research offers an effective method for constructing an efficient S-Scheme photocatalytic system for H2 evolution.

Intrinsic time resolution and efficiency study for simulated scintillators plastics with Geant4

The time resolution (TR) is one of the most important characteristic of a detector. The particular case of a scintillator, the collection of light also is important, it depends of the sensitive area of the photo-sensor (Scorer). Normally, the Scorer of Photomultipliers Tubes (PMTs) is greater than the Scorer of Silicon Photomultipliers (SiPMs). Other differences are the voltage of operation, their size and cost, in some cases, the large size of PMTs can be difficult to place, if small space is required, in which case, it is preferable to use SiPMs. The value of TR also depends of the size and geometry of thescintillator, number of photo-sensors and the electronic part.In this work, we study the mean optical photon arrival time distribution (AT) to a Scorer from a SiPM of 6X6 mm2. We define the variation of AT as the intrinsic time resolution (ITR). In Geant4, we simulated two different geometries: square and hexagonal, for a BC-404 plastic scintillator coupled to one Scorer. The sources simulated were Sr90, Co60, Cs137, Na22 and μ- of 1 GeV. It is shown that AT and ITR depends of the geometry and size of the plastic scintillator, the location of the Scorer, the incident particle and its energy. Then, the ITR and therefore the TR is not a constant for a detector. Finally, we show the relation between AT and the deposited energy by the particle incident, which are related in the experiment to the response time event of the detector and the deposited charge by the incident particle, respectively.

Evaluation of plastic scintillating fibers coating technique for muon imaging detector using a Compton-coincidence-technique system

This study is devoted to studying the performance of plastic scintillating fibers (PSFs) for a high-position-resolution muon imaging detector. A test system based on the Compton coincidence technique is designed to study the light collection of the PSFs. When Compton scattering occurs between the PSFs and gamma ray emitted by the collimated radioactive source, the PSF detector has detected the definite energy of recoiled electrons, and the coincidence detector has detected the energy of scattered photons. Four groups of PSFs were tested, three of which were wrapped with the Enhanced Specular Reflector (ESR) in different ways. The experimental results show that the light collection of the PSF detector can be increased by wrapping the PSFs with ESR and leaving an air gap between the PSF and the ESR. Meanwhile, the light collection is increased while the position where Compton scattering occurs in the PSF is closer to the silicon photomultiplier (SiPM). This study provides a method for measuring the light collection in narrow PSFs. In conclusion, the presence and fine wrapping of the ESR ensure the isolation and position accuracy in the arrays of PSFs.

Diamond immersion photodetector for 213 nm deep-ultraviolet photodetection

Developing a photoelectric detector with independent power, compactness, and high environmental sensitivity is a key step to realize the energy-saving and sustainable integrated photoelectric system of next generation. In this paper, a p-type diamond single crystal (PDSC) is used as the photoelectrode to construct a self-powered deep ultraviolet light immersion photodetector with the photoelectrochemical (PEC) cell structure. Under the excitation of a deep ultraviolet light of 213 nm, this immersion photodetector exhibits an excellent responsivity of 20 mA W−1 and a short response/recovery time (50/38 ms). This superior performance is attributed to the successful synthesis of high-quality p-type diamond by the high-temperature and high-pressure method, which ensures an efficient light detection through the effective light collection. This kind of immersion detector based on the ultra-wide-bandgap diamond guarantees a stable detection for deep ultraviolet detection with efficient response, which displays a great potential in future application.

Discrimination of Fast and Thermal Neutrons Using a Novel Phoswich Detector of LaCl3 and LiI:Eu Single Crystal Scintillators

A novel phoswich detector was setup by employing LaCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> + LiI:Eu single crystal scintillators and was characterized in details for its performance with Am-Be, D-D and D-T neutron sources. LaCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystal shows transparency to the scintillation emission of LiI:Eu for light collection to PMT. Thermal and fast neutrons were successfully discriminated by pulse shape discrimination (PSD) with high value of figure of merit of 5.5 due to significant difference of their scintillation kinetics.

Glutathione-sensitized SnS2 nanoflake/CdS nanorod heterojunction for enhancing cathodic protection of 304 stainless steel with remarkable photoelectric conversion performance

An effective way to enhance photochemical performance can be achieved by optimizing the microstructure of composite semiconductor materials. Here, a two-step hydrothermal method was used to synthesize SnS2/CdS composite photoanodes for photocathode protection applications, and glutathione was introduced as a structure-directing agent to enhance the separation efficiency of photogenerated electron-hole pair of SnS2/CdS. In the presence of glutathione, SnS2 became a smaller and thinner nanoflake and hexagonal CdS extended into a rod shape, the combination of them resulted in larger light collection area and higher charge transfer rate. The electrochemical test results demonstrated that the open circuit potential of 304 SS coupled with SnS2/CdS/GSH photoanode was negatively shifted to about −0.5 V under light, which not only far exceeded the self-corrosion potential of 304 SS (-0.18 V), but also improved from −0.42 V of SnS2/CdS. Further, the photogenerated current density of SnS2/CdS/GSH was nearly three times that of SnS2/CdS, EIS and polarization curve results also indicated that glutathione enhances the PEC performance of SnS2/CdS. Obviously, the type-II heterojunction formed by glutathione-sensitized SnS2/CdS provides more electrons for 304 SS, which is beneficial to achieve better photocathodic protection.

Accounting for effective specularity in the DETECT2000 program when determining light collection coefficients using NaI(Tl) and BGO scintillators as an example

Accounting for effective specularity in the DETECT2000 program when determining light collection coefficients using NaI(Tl) and BGO scintillators as an example