Optical Collection Efficiency Research Articles

Optical photon transport simulations for SiPM based PET scanner

Positrons emitted from radioisotope quickly annihilates to two collinear photons that are captured by the array of scintillator detectors to infer about the origin of radioactivity. Coincidence collection of pair of points from the detector modules makes a line of response, their large number reveals a radioactive region of interest. Most of the medical diagnostic research is conducted with position sensitive imaging device whose performance strongly depends on the optical light collection efficiency. A versatile Lutetium–Yttrium Oxyorthosilicate (LYSO) scintillator is used to mimic the optical photon production and transport processes followed by the light collection with Silicon PhotoMultiplier sensor. Charge spectrum from a 2 × 2 × 10 mm3 single LYSO bar is obtained in GEANT4, and reproduces well the scintillation characteristics of LYSO along with photons incidence angle distribution with a single SiPM pad. This excercise is followed by the simulation performance of two PET modules comprises of 12 × 12 SiPM tile coupled with mesh of LYSO bars. The preliminarly results shows the transverse position resolution (FWHM) as 7.82 mm for a point source. Objective of this study is to search for a cheaper detector solution which will have equivalent imaging performance.

Scalable fabrication of hemispherical solid immersion lenses in silicon carbide through grayscale hard-mask lithography

Grayscale lithography allows the creation of micrometer-scale features with spatially controlled height in a process that is fully compatible with standard lithography. Here, solid immersion lenses are demonstrated in silicon carbide using a fabrication protocol combining grayscale lithography and hard-mask techniques to allow nearly hemispherical lenses of 5μm radius to be etched into the substrate. Lens performance was benchmarked by studying the enhancement obtained in the optical collection efficiency for single quantum emitters hosted in silicon carbide. Enhancement by a factor of 4.4 ± 1.0 was measured for emitters not registered to the center of the lens, consistent with devices fabricated through other methods. The grayscale hard-mask technique is highly reproducible, scalable, and compatible with CMOS technology, and device aspect ratios can be tuned after resist patterning by controlling the chemistry of the subsequent dry etch. These results provide a reproducible, low-cost, high-throughput and industrially relevant alternative to focused ion beam milling for the creation of high-aspect-ratio, rounded microstructures for quantum technology, and microphotonic applications.

NV-plasmonics: modifying optical emission of an NV− center via plasmonic metal nanoparticles

Abstract The nitrogen-vacancy (NV) center in diamond is very sensitive to magnetic and electric fields, strain, and temperature. In addition, it is possible to optically interrogate individual defects, making it an ideal quantum-limited sensor with nanoscale resolution. A key limitation for the application of NV sensing is the optical brightness and collection efficiency of these defects. Plasmonic resonances of metal nanoparticles have been used in a variety of applications to increase the brightness and efficiency of quantum emitters, and therefore are a promising tool to improve NV sensing. However, the interaction between NV centers and plasmonic structures is largely unexplored. In particular, the back-action between NV and plasmonic nanoparticles is nonlinear and depends on optical wavelength, nanoparticle position, and metal type. Here we present the general theory of NV-plasmonic nanoparticle interactions. We detail how the interplay between NV response, including optical and vibrational signatures, and the plasmonic response of the metal nanoparticle results in modifications to the emission spectra. Our model is able to explain quantitatively the existing experimental measurements of NV centers near metal nanoparticles. In addition, it provides a pathway to developing new plasmonic structures to improve readout efficiencies in a range of applications for the NV center. This will enable higher precision sensors, with greater bandwidth as well as new readout modalities for quantum computing and communication.

Performance of Luminescent Solar Concentrators Integrated with Negative Replica Layers of Leaf Surface Microstructures.

In this study, a negative replica layer of leaf surface microstructures was used to cover the top surfaces of semitransparent thin-film luminescent solar concentrators (LSCs) to enhance the concentrators’ performance. With low reflection on the air–glass interface of the glass plate in a thin-film LSC, a negative replica layer enables the scattering of incident sunlight and increases the path of light transmitted into the LSC and the thin phosphor layer at the bottom surface of the LSC. The incident sunlight is therefore more likely to interact with the phosphor particles in the thin-film phosphor layer, thereby enhancing the performance of the LSC. In this study, semitransparent thin-film LSCs with different inorganic phosphors were examined. The experimental results revealed that the optical collection efficiency of semitransparent thin-film LSCs covered with negative replica layers of leaf surface microstructures was higher than that of the semitransparent thin-film LSCs without negative replica layers. Furthermore, the LSCs with negative replica layers with high haze ratios exhibited high optical collection efficiency. Integrating negative replica layers of leaf surface microstructures as semitransparent layers in thin-film LSCs may optimize the application of LSCs in building-integrated photovoltaics (BIPVs).

Multiplexed Sensing of Magnetic Field and Temperature in Real Time Using a Nitrogen-Vacancy Ensemble in Diamond

Nitrogen-Vacancy (NV) spin in diamond is a versatile quantum sensor, being able to measure physical quantities such as magnetic field, electric field, temperature, and pressure. In the present work, we demonstrate a multiplexed sensing of magnetic field and temperature. The dual frequency driving technique we employ here is based on frequency-division multiplexing, which enables sensing both measurables in real time. The pair of NV resonance frequencies for dual frequency driving must be selected to avoid coherent population trapping of NV spin states. With an enhanced optical collection efficiency higher than 50 $\%$ and a type 1b diamond crystal with natural abundance $^{13}$C spins, we achieve sensitivities of about 70 pT/$\sqrt{\mathrm{Hz}}$ and 25 $\mu$K/$\sqrt{\mathrm{Hz}}$ simultaneously. A high isolation factor of 34 dB in NV thermometry signal against magnetic field was obtained, and we provide a theoretical description for the isolation factor. This work paves the way for extending the application of NV quantum diamond sensors into more demanding conditions.

MRI Compatible Fiber Optic Multi Sensor Platform for Real Time Vital Monitoring

Microsystems sensors are implemented on a fiber optics based platform towards use in magnetic resonance imaging assisted interventions. The presented platform offers real-time and in-situ pressure, temperature, and localization feedback during imaging assisted surgical procedures. This multi-sensor platform fits into an interventional medical device with a diameter of 2.5 mm. A polymer cap with perforation is utilized for circulation of blood in the vessel to allow correct monitoring of the temperature and pressure in real time. Graded Index (GRIN) lenses were utilized at the tip of the fiber cables improved optical signal collection efficiency. Three light sources having different wavelengths were utilized each for one sensor; a 637 nm laser, a 780 nm laser, and a 875 nm LED (50 nm bandwidth) for pressure, localization, and temperature sensors, respectively. Pressure sensing is performed by a released polymer-metal hybrid membrane having a diffraction grating interferometer readout scheme. Temperature sensing is accomplished based on the change of absorption and transmission in semiconductors (i.e. GaAs) due to variations of energy bandgap with temperature. Localization of the medical device is acquired based on magneto-optical Kerr effect where Iron Oxide magnetic material is employed. The sensor chip revealed a temperature precision of ±0.22 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C, a pressure resolution of 1 mmHg and a localization resolution of 3 mm, where all values are relevant to medical practice. Integration of the sensors developed in this study helps medical devices such as catheters and stents, allow a new horizon in interventional surgery.

Construction strategy and performance analysis of large-scale spherical solar concentrator for the space solar power station

The space solar power station is a gigantic power satellite to provide the earth with continuous energy. The front-end system of space solar power station, solar concentrator, has significant influences on the optical performance. Regarding the proposed orb-shaped membrane energy gathering array scheme, this paper deals with the construction strategy of its large-scale spherical concentrator to reduce the complexity of manufacturing and improve the optical properties. The optical principle of the spherical concentrator is described and the spatial motion characteristic is presented. A novel construction strategy for the large-scale concentrator is proposed via partitioning octahedron on the sphere and polygonal partition. This paper evaluates the optical performance of the concentrator constructed by the novel strategy using ray tracing method. Performance parameters such as optical concentration ratio and collection efficiency are obtained. Comparison with the other strategies are also implemented. In addition, influence factors such as the sun's non-parallelism, the tracking precision, the orbital periodic motion, and the potential blockage effects of microwave transmitting antenna and supporting structure are mathematically discussed and evaluated. The numerical results indicate that the proposed strategy achieves a high collection rate, a small efficiency fluctuation, appropriate energy distribution, and relatively small splicing modules, which is conducive to improve optical performance and decrease difficulty in manufacturing.

A high-performance cupric oxide photocatalyst with palladium light trapping nanostructures and a hole transporting layer for photoelectrochemical hydrogen evolution

The high recombination rate of photogenerated electron–hole pairs, poor photocorrosion stability, and the discrepancy between the optical absorption length and charge collection efficiency of cupric oxide (CuO) are the main limiting factors of CuO photocatalysts.

Design and characterization of a package-less hybrid PDMS-CMOS-FR4 contact-imaging system for microfluidic integration.

We demonstrate a hybrid "package-less" polydimethylsiloxane (PDMS)-complementary-metal-oxide-semiconductor (CMOS)-FR4 system for contact imaging. The system embeds the CMOS image sensor directly in a PDMS layer instead of the standard chip package to support microfluidic structures much larger and more complex than those in prior art. The CMOS/PDMS layer is self-aligned to form a continuous, flat surface to provide structural support for upper microfluidic layers. The system consists of five layers of PDMS implementing fluid channels, valves, chambers, and inlets/outlets. A custom CMOS image sensor with integrated signal conditioning circuits directly captures light from sample fluid for high optical collection efficiency. Owing to the flexibility afforded by the integration process, the system demonstrates, for the first time, integrated valves in contact imaging. Moreover, we present the first direct comparison of the optical performance of a CMOS image sensor and a photomultiplier tube (PMT) in identical contact-imaging conditions. Measurements show that our CMOS sensor achieves 17 dB better signal-to-noise ratio (SNR) compared to a commercial PMT across a broad range of integration times, with a maximum SNR of 47 dB. Chemiluminescent testing successfully shows signal detection for different analyte concentrations and integration times. The contact-imaging system demonstrates a detection limit of 25 μM of a 9,10-diphenylanthracene-based solution.

Enhanced Detection of Single Viruses On-Chip via Hydrodynamic Focusing.

Planar optofluidics provide a powerful tool for facilitating chip-scale light-matter interactions. Silicon-based liquid core waveguides have been shown to offer single molecule sensitivity for efficient detection of bioparticles. Recently, a PDMS based planar optofluidic platform was introduced that opens the way to rapid development and prototyping of unique structures, taking advantage of the positive attributes of silicon dioxide-based optofluidics and PDMS based microfluidics. Here, hydrodynamic focusing is integrated into a PDMS based optofluidic chip to enhance the detection of single H1N1 viruses on-chip. Chip-plane focusing is provided by a system of microfluidic channels to force the particles towards a region of high optical collection efficiency. Focusing is demonstrated and enhanced detection is quantified using fluorescent polystyrene beads where the coefficient of variation is found to decrease by a factor of 4 with the addition of hydrodynamic focusing. The mean signal amplitude of fluorescently tagged single H1N1 viruses is found to increase with the addition of focusing by a factor of 1.64.

Lithium use among psychiatric patients–a risk factor for hypernatremia?

As part of the Mars Science Laboratory, the ChemCam instrument acquires remote laser induced breakdown spectra at distances that vary between 1.56 m and 7 m. This variation in distance affects the intensities of the measured LIBS emission lines in non-trivial ways. To determine the behavior of a LIBS emission line with distance, it is necessary to separate the effects of many parameters such as laser energy, laser spot size, target homogeneity, and optical collection efficiency. These parameters may be controlled in a laboratory on Earth but for field applications or in space this is a challenge. In this paper, we show that carefully selected ChemCam LIBS emission lines acquired from the Martian dust can be used to build an internal proxy spectroscopic standard. This in turn, allows for a direct measurement of the effects of the distance of various LIBS emission lines and hence can be used to correct ChemCam LIBS spectra for distance variations. When tested on pre-launch LIBS calibration data acquired under Martian-like conditions and with controlled and well-calibrated targets, this approach yields much improved agreement between targets observed at various distances. This work lays the foundation for future implementation of automated routines to correct ChemCam spectra for differences caused by variable distance.

Physics and devices of quanutm light emission from semicoductor self-assembled quantum Dots

Self-assembled semiconductor single quantum dots (QDs), as a good candidate of solid-state real single photon (SP) emitters in high purity and counting rate, have attracted great attention in recent two decades, promising for quantum information, optical quantum computation, quantum storage, and quantum coherent manipulation. To isolate single QD from the other QDs surrounding, 1) dilute QD density is well controlled during epitaxy; 2) micro-pillars or nanowires individually in space as hosts are fabricated. To enhance their uni-directional emission, GaAs/AlAs distributed Bragg reflector (DBR) planar cavity is integrated. To improve the system (i.e. confocal microscope, traditionally) stability and its optical collection efficiency, a near-field fiber coupling by adhering a micro-pillar chip to fiber facets directly is used. To enhance the coherence of QD spontaneous emission, resonant excitation technique is applied. In this article, we review our research progress in self-assembled QD SP emission, including SP emission from InAs or GaAs QDs on Ga droplet-self-catalyzed GaAs nanowires (with g2(0) of 0.031 or 0.18, respectively), SP emission from InAs/GaAs QDs coupled with high-Q (1000-5000) DBR micro-pillar cavities and their fiber-coupled device fabrication with SP fiber output rate ~1.8 MHz, single QD resonant fluorescence with inter-dot coherent visibility of 40%, strain-coupled bilayer InAs QDs to extend their emission wavelength to 1320 nm and parametric down conversion of 775 nm SP emission from single QD in nanowire to realize entangled photon pairs at 1550 nm (entanglement fidelity of 91.8%) for telecomm application, and definite quantum storage of InAs QD SPs at 879 nm in ion-doped solid (at most 100 time-bins). In future, there will be still several urgent things to do, including 1) puring the environment of a single QD (e.g. growing GaAs QDs to avoid the wetting layer, and optimizing QD growth to avoid smaller QDs) to reduce its spectral diffusion and developing a high-symmetric QD (e.g. GaAs QD) to reduce the fine structure splitting of its emission; 2) positioning single QD precisely for a good alignment of single QD to a micro-cavity or fiber cone (single mode with high numerical aperture) to increase optical excitation efficiency and SP collection efficiency; 3) developing optical quantum integrated chip, including hybrid structures of active micro-cavity and passive waveguide, and high-transmission waveguide beamsplitter or Mach-Zender interferometer to improve SP extraction (micro-cavity), collection (optical setup) and counting rate (at avalanched photon detectors and coincidence counting module).

Assessment of optical photon collection in a large plastic scintillator using Geant4-Gate code

The scintillating detectors are widely used in both X-ray and gamma-ray imaging systems. Optical photon collection has a significant impact on the scintillation gamma-ray spectrum. Besides, by increasing the size of scintillator, optical photon collection becomes more important. In this work, a suitable arrangement of photomultiplier tubes (PMTs) and an appropriate reflector for a large plastic scintillator whose dimensions were 122 cm × 18 cm × 6 cm were designed. For this aim, two types of reflectors (aluminum foil and Teflon tape) and three different arrangements of four PMTs were studied. All simulations were carried out by Geant4-Gate code. The simulations showed that the scintillator with the aluminum foil coverage has a better spatial uniformity response than the others. In fact, in this sample the counting efficiency and optical photon collection efficiency were relatively better than the other samples. The symmetrically arrangement of PMTs on 18 cm × 6 cm faces of the scintillator with the aluminum foil coverage was the best arrangement of PMTs and reflector for the large plastic scintillator. The spatial uniformity of total response at this sample is 70-fold better than the similar arrangement with Teflon tape coverage. Thus, this arrangement of PMTs on the scintillator surface and aluminum foil coverage can be used in an X-ray backscatter imaging system.

Chirped circular dielectric gratings for near-unity collection efficiency from quantum emitters in bulk diamond

Efficient collection of fluorescence from nitrogen vacancy (NV) centers in diamond underlies the spin-dependent optical read-out that is necessary for quantum information processing and enhanced sensing applications. The optical collection efficiency from NVs within diamond substrates is limited primarily due to the high refractive index of diamond and the non-directional dipole emission. Here we introduce a light collection strategy based on chirped, circular dielectric gratings that can be fabricated on a bulk diamond substrate to modify an emitter’s far-field radiation pattern. Using a genetic optimization algorithm, these grating designs achieve 98.9% collection efficiency for the NV zero-phonon emission line, collected from the back surface of the diamond with an objective of aperture 0.9. Across the broadband emission spectrum of the NV (600–800 nm), the chirped grating achieves 82.2% collection efficiency into a numerical aperture of 1.42, corresponding to an oil immersion objective again on the back side of the diamond. Our proposed bulk-dielectric grating structures are applicable to other optically active solid state quantum emitters in high index host materials.

Lead foil wrapping of the plastic scintillators for the gamma ray detection: optical reflector or spectrum intensifier?

This paper studies the effect of lead wrapping on the response of the plastic scintillators as gamma detectors. Experimental tests and Geant4 simulations showed that lead wrapping cannot increase the gamma absorption efficiency of the detector but, as a reflector, it can improve the optical properties of the detector. The reflectivity of the lead foil as an optical reflector was determined equal to 66% using an experimental-simulation combined method. Based on the obtained results, the optical collection efficiency of the detector was also increased about 4% after employing the lead reflector.

Multi‐Watt high‐power THz frequency quantum cascade lasers

Multi-Watt high-power terahertz (THz) frequency quantum cascade lasers are demonstrated, based on a single, epitaxially grown, 24-μm-thick active region embedded into a surface-plasmon waveguide. The devices emit in pulsed mode at a frequency of ∼4.4 THz and have a maximum operating temperature of 132 K. The maximum measurable emitted powers from a single facet are ∼2.4 W at 10 K and ∼1.8 W at 77 K, with no correction being made for the optical collection efficiency of the apparatus, or absorption by the cryostat polyethylene window.

快速实现矩形准直光束的高集光效率LED透镜设计

快速实现矩形准直光束的高集光效率LED透镜设计

LED Lens for Rectangular Beam with Small Divergence Angles

We have designed a new TIR(Total Internal Reflection) structure for generating an LED lens which can produce a rectangular beam with small divergence angle in two perpendicular directions for an optical guidance system. The lens can control the divergence angle in the horizontal direction to be a small value of about 8° with a 1 mm × 1 mm LED source, also in the vertical direction it can be about 7°, with optical collection efficiency higher than 0.83. After the lens is manufactured, the work demonstrates that the lens is suitable for an optical guidance system.

Fabrication of the glass microlens arrays and the collimating property on nanolaser

The influence of the glass microlens array on the collection efficiency and beam collimating with the ZnO/GaN nanoheterojunction nanolaser is investigated. Ultraviolet random lasing behavior from the ZnO/GaN nanoheterojunction array has been demonstrated with both optical and electrical pumping. The refractive microlens arrays are designed and fabricated on the glass slide using the microfabrication procedures and integrated on the nanolaser. We show that, for the nanolaser with divergent output beams, the introduction of glass microlens arrays reduces the beam divergence and increases transmission. The detected optical power is enhanced by more than 1.8 times for the nanolaser integrated with glass microlens arrays. The drastic increase in the optical collection efficiency is resulted from the laser beam collimating.

Structural evolution of NM (Ni and Mn) lithium-rich layered material revealed by in-situ electrochemical Raman spectroscopic study

Li-rich layered materials are one of promising candidates of cathode materials for energy storage in electric vehicles (EVs) due to their high energy density. The practical application of these materials relies on the in-depth understanding of the crystal structures and reaction mechanisms during the electrochemical processes to overcome the potential decay issue. In this work, in-situ electrochemical Raman spectroscopy has been developed and used to investigate the structural evolution of the Li-rich layered material (0.5LiNi0.5Mn0.5O2·0.5Li2MnO3). An electrochemical Raman spectroscopic cell with an excellent air-tightness and optical signal collection efficiency has been designed and used for in-situ investigation of the NM Li-rich material during the very first two electrochemical cycles. We found that the reactions of Ni2+ to Ni3+ and Ni3+ to Ni4+ appearing in the potential range of from 3.70 V to 4.45 V show a good reversibility. The in-situ Raman spectra after the first two electrochemical cycles also indicate the activation of Li2MnO3 changes the ionic local coordination structure and increases the ionic disorder of the pristine NM Li-rich layered material. This structural change has a great impact on the subsequent electrochemical cycles. The in-situ Raman spectroscopy results can help to improve the performance of NM Li-rich layered materials.