Variation Of Light Output Research Articles

Effects of Temporal Light Modulation on Cognitive Performance,Eye Movements, and Brain Function

ABSTRACT Temporal light modulation (TLM) describes variations in light output from a light source or lighting system and can be a characteristic of their normal operation. TLM at 100 or 120 Hz can disrupt eye movements and reduce visual performance compared to 40 kHz, but little is known of the effects between those frequencies. Such evidence could provide the basis for lighting product and application standards to support the development of energy-efficient lighting systems. This repeated-measures experiment compared the effects of three stimuli (no TLM [DC], 100 Hz, and 500 Hz [both rectangular-wave, 100% modulation depth, 50% duty cycle]) on state anxiety, eye movements (blinks, saccades, fixations, and pupil size), cognitive performance (Stroop task and sentence reading speed), and visual event-related potentials (ERPs). Post-processing of EEG data included dipole source analysis and estimates of source dipole strength. TLM at 100 Hz was associated with larger pupil sizes and greater ERP dipole strength during 100 Hz exposure than no TLM, particularly in the right hemisphere. Cognitive interference was lower for 500 Hz TLM than 100 Hz. State anxiety was unaffected. The addition of TLM to the light source signal increased arousal and altered brain activity; at the highest frequency tested here this reduced cognitive interference. Arousal theory and stochastic facilitation can provide possible explanations.

Flexible liquid light-guide-based radiation sensor with LaBr3:Ce scintillator for remote gamma-ray spectroscopy

In this study, we fabricated a liquid light-guide-based radiation sensor with a LaBr3:Ce scintillator for remote gamma-ray spectroscopy. We acquired the energy spectra of Cs-137 and Co-60 using the proposed sensor, estimated the energy resolutions of the full energy peaks, and compared the scintillation light output variations. The major peaks of the radionuclides were observed in each result, and the estimated energy resolutions were similar to that of a general NaI(Tl) scintillation detector without a liquid light guide. Moreover, we showed the relationships of energy resolution and analog-to-digital channel regarding the number of photoelectrons produced and confirmed the effects of light guide length on remote gamma-ray spectroscopy. The proposed sensor is expected to be utilized to perform remote gamma-ray spectroscopy for distances of 3 m or more and would find application in many fields of nuclear facilities and industry.

Properties of the CsI(Tl) detector elements of the CALIFA detector

In the R3B experiment at FAIR, charged particles with energies up to 600 MeV and forward boosted γ-rays with energies up to 20 MeV need to be detected in scattering experiments. Calorimeters for nuclear physics experiments of this kind, using relativistic radioactive ion beams, require high energy resolution and high efficiency for simultaneous detection of strongly Doppler shifted γ-rays and high-energy charged particles. A calorimeter design that can meet these requirements, using CsI(Tl) scintillators, results in detector elements that may exhibit light output variations with crystal depth, which can limit the attainable resolution. In this paper we present results from a systematic study of 478 detector modules of CALIFA, the R3B calorimeter, in order to determine and minimize such variations. To facilitate further systematic studies we also present results for the total absorption length of the scintillation light, using spectrophotometry, light crosstalk between adjacent detector modules, and surface topography of the CsI(Tl) crystals from atomic force microscopy.

Advanced optical simulation of scintillation detectors in GATE V8.0: first implementation of a reflectance model based on measured data

Typical PET detectors are composed of a scintillator coupled to a photodetector that detects scintillation photons produced when high energy gamma photons interact with the crystal. A critical performance factor is the collection efficiency of these scintillation photons, which can be optimized through simulation. Accurate modelling of photon interactions with crystal surfaces is essential in optical simulations, but the existing UNIFIED model in GATE is often inaccurate, especially for rough surfaces. Previously a new approach for modelling surface reflections based on measured surfaces was validated using custom Monte Carlo code. In this work, the LUT Davis model is implemented and validated in GATE and GEANT4, and is made accessible for all users in the nuclear imaging research community. Look-up-tables (LUTs) from various crystal surfaces are calculated based on measured surfaces obtained by atomic force microscopy. The LUTs include photon reflection probabilities and directions depending on incidence angle. We provide LUTs for rough and polished surfaces with different reflectors and coupling media. Validation parameters include light output measured at different depths of interaction in the crystal and photon track lengths, as both parameters are strongly dependent on reflector characteristics and distinguish between models. Results from the GATE/GEANT4 beta version are compared to those from our custom code and experimental data, as well as the UNIFIED model. GATE simulations with the LUT Davis model show average variations in light output of <2% from the custom code and excellent agreement for track lengths with R2 > 0.99. Experimental data agree within 9% for relative light output. The new model also simplifies surface definition, as no complex input parameters are needed. The LUT Davis model makes optical simulations for nuclear imaging detectors much more precise, especially for studies with rough crystal surfaces. It will be available in GATE V8.0.

SU‐E‐T‐672: Real‐Time In Vivo Dosimeters Using LiPCDA and Optical Fibers

Purpose:To investigate dosimeter prototypes made with lithium pentacosa‐10,12‐diynoate (LiPCDA, the material used in GafChromic EBT films) and optical fibers for their suitability in real‐time in vivo measurements.Methods:The prototypes, made with 500 µm plastic optical fibers and 8.5 µm thickness of LiPCDA at fiber tip, were irradiated with a 6 MV beam. To investigate the efficacy of pre‐irradiation calibration, the probes were irradiated to 2 Gy twice, with 5 minutes in between. Net optical density values (netOD) around the main absorbance peak were compared, and effect of correcting second measurement by the first was assessed. Ageing was assessed by irradiating two prototypes to 2 Gy and comparing the netOD to that obtained for 15 prototypes from the same batch 12–14 months earlier. To measure angular dependence, the probes were pre‐irradiated with beam perpendicular to fiber axis and then, 5 minutes later either perpendicular or parallel to fiber axes. The thickness‐corrected netOD measurements were compared.Results:Standard deviation of netOD for probes of the same batch was measured to be 5–6%. When netOD was corrected for material thickness by using results from the first irradiation, the standard deviation decreased to 1.3%. This was comparable to the uncertainty in measurements observed with a single probe and is attributed to variations in light output, spectrometer noise and splitter‐to‐probe connection variations. Comparison of netOD values obtained a year apart failed to illustrate statistically significant decrease in sensitivity due to ageing (0.38 ± 0.03 and 0.3656 ± 0.0003). NetOD measured with MV beam parallel to fiber was within error of netOD measured with MV beam perpendicular to fiber.Conclusion:Current prototype construction allows for shelf life of at least one year. With material thickness corrected for, the prototypes can measure dose with an uncertainty below 2% at a given energy and dose rate.This work has been funded by the Ontario Centres of Excellence Market Readiness grant. The authors have no conflict of interest to declare.

Characteristics of Lu$_{1.8}$Gd$_{0.2}$SiO$_{5}$:Ce (LGSO) for APD-Based PET Detector

Since its discovery in 1993, LGSO has been seen as a promising scintillator for positron emission tomography (PET) imaging. Recently, new high lutetium content Lu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.8</sub> Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> :Ce (LGSO-90%Lu) has been produced with Ce concentration varying from 0.025 to 0.75 mol% Ce, yielding decay times in the range of 34.2 to 44.8 ns. These scintillators could potentially be used as phoswich detectors in PET for improving spatial resolution. To validate this assumption, light output, energy resolution, temperature dependence, timing resolution, and pulse-shape discrimination performance were assessed. The light output of these LGSO scintillators is 3.5 to 4.8 times higher than BGO with avalanche photodiode readout [7.5 to 8 times with photomultiplier tube (PMT)] and increases with Ce concentration. The variation of light output for temperature ranging from 10 to 50 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C is less than 18% with PMT readout. Energy resolution at 662 keV is about 11% (10%) with avalanche photodiode (APD) (PMT) readout. Timing resolution with APD is ~ 1.65 ns for all samples relative to a fast PMT-plastic detector. Pulse-shape discrimination of LGSO-90% Lu with 0.025 mol% Ce (¿ = 34.2 ns) and 0.75 mol% Ce (¿ = 44.8 ns) was successfully achieved in a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">phoswich</i> assembly, making this new high lutetium content LGSO with adjustable decay time constants a strong candidate for a high-resolution depth-of-interaction detector intended for PET imaging.

Development of tin-loaded liquid scintillator for the double beta decay experiment

Tin-loaded liquid scintillator offers some advantages as a detector for double beta decay experiment. A research program was carried out with the objective of developing such scintillators. Several organometals were loaded into pseudocumene-based liquid scintillator (LS) and light output variation was studied. Up to 50% of tetramethyltin (32.6% w of tin) was successfully loaded into LS and light output was as high as 57% of unloaded LS. We have studied the characteristics and stability of the one liter tin-loaded LS contained in a Teflon vessel. Several γ -ray radioactive sources were used for energy calibration and calibration data were compared with Monte Carlo simulation. Data-taking at the 700 m underground laboratory in Yangyang is ongoing for the search of 0 ν β β decay of 124Sn.

Monte Carlo and Lambertian light guide models of the light output from scintillation crystals at megavoltage energies

A new model of the light output from single-crystal scintillators in megavoltage energy x-ray beams has been developed, based on the concept of a Lambertian light guide model (LLG). This was evaluated in comparison with a Monte Carlo (MC) model of optical photon transport, previously developed and reported in the literature, which was used as a gold standard. The LLG model was developed to enable optimization of scintillator detector design. In both models the dose deposition and light propagation were decoupled, the scintillators were cuboids, split into a series of cells as a function of depth, with Lambertian side and entrance faces, and a specular exit face. The signal in a sensor placed 1 and 1000 mm beyond the exit face was calculated. Cesium iodide (CSI) crystals of 1.5 and 3 mm square cross section and 1, 5, and 10 mm depth were modeled. Both models were also used to determine detector signal and optical gain factor as a function of CsI scintillator thickness, from 2 to 10 mm. Results showed a variation in light output with position of dose deposition of a factor of up to approximately 5, for long, thin scintillators (such as 10 X 1.5 x 1.5 mm3). For short, fat scintillators (such as 1 X 3 X 3 mm3) the light output was more uniform with depth. MC and LLG generally agreed to within 5%. Results for a sensor distance of 1 mm showed an increase in light output the closer the light originates to the exit face, while a distance of 1000 mm showed a decrease in light output the closer the light originates to the exit face. For a sensor distance of 1 mm, the ratio of signal for a 10 mm scintillator to that for a 2 mm scintillator was 1.98, whereas for the 1000 mm distance the ratio was 3.00. The ratio of quantum efficiency (QE) between 10 and 2 mm thicknesses was 4.62. We conclude that these models may be used for detector optimization, with the light guide model suitable for parametric study.

Energy spectra analysis of the four-layer DOI detector for the brain PET scanner: jPET-D4

A depth of interaction (DOI) detector is being developed for the brain PET scanner, jPET-D4. We introduce a light output correction procedure to compensate for variations among the crystal elements in the DOI detector. Under uniform irradiation with 511 keV gamma rays, we estimate the light output of each crystal element by identifying each crystal element, and generate a look-up table (LUT) for light output correction. We evaluate the energy resolution of all crystal elements. The energy resolution of 16% is achieved after light output correction for all crystal elements. The DOI detector can correct light output variations that are related to the DOI. We analyze the crystal position dependence of the energy spectra due to inter-crystal scattering among the multiple crystal elements in the DOI detector. It is highly possible that gamma rays interacting with central crystal elements in the crystal array are absorbed by surrounding crystal elements and the Compton part of the energy spectrum is decreased. Inter-crystal scattering has less impact on the energy resolution of the DOI detector.

Energy resolution and energy–light response of CsI(Tl) scintillators for charged particle detection

This article describes the crystal selection and quality control utilized to develop and calibrate a high-resolution array of CsI(Tl) scintillator crystals for the detection of energetic charged particles. Alpha sources are used to test the light output variation due to thallium doping gradients. Selection of crystals with better than 1% non-uniformity in light output is accomplished using this method. Tests with a 240 MeV alpha beam reveal that local light output variations within each of the tested CsI(Tl) crystals limit the resolution to about 0.5%. Charge and mass dependences in the energy–light output relationship are determined by calibrating with energetic projectile fragmentation beams.

Performance of undoped BGO crystals under extremely high dose conditions

We checked the performance of undoped BGO crystals under extremely high dose conditions (dosage up to 88 Mrad). The light outputs of the crystals drop by ∼30% after receiving 10 Mrad of γ-ray dose but remain stable throughout the rest of the test. The self-recovery behavior of BGO under 20 Mrad has also been studied. The reduced variation in light output from pre-radiated BGOs, together with a fixed recovery limit, indicate that a pre-radiation process may be helpful to stabilize the BGO performance in a low dose environment.

Survey of mammographic cassette light output.

The purpose of the present paper was to assess the variation in light output from clinical mammographic screens, particularly in relationship to age and radiographic usage. The light output from 156 mammographic cassettes from 17 clinical centres was measured on site using a novel light detector. Survey information on cassette age and usage was collected. Where possible, screen manufacture date was supplied by the vendor. One cassette from each centre was measured at a standard laboratory to allow normalization of all measurements. Three centres were found to have cassettes in clinical use whose light outputs varied by an amount incompatible with current Royal Australasian College of Radiologists (RACR) standards. These centres used cassettes whose ages varied widely. No correlation between light output and radiographic usage was found. Older cassettes were found to have a slight increase in light output. A small reduction of light output was measured between screen regions of high and low radiation exposure histories. Replacement of mammographic screens should not be based on an expectation of light output reduction due to age or usage. Rather, all mammographic screens should be replaced simultaneously as indicated by factors such as failure of screen-film contact or the presence of screen-related image artefacts.

Emission characteristics of two-polymer layer electroluminescent devices operating under various duty cycles

We report the emission characteristics of two-polymer layer electroluminescent devices, fabricated from poly( p-phenylenevinylene) and a solution-processable poly(cyanoterephthalylidene), driven using pulsed voltages. Current, luminance and response times were measured as a function of drive voltage. A peak pulsed luminance of 10 4 cd m −2 was achieved at a current density of 1.5 A cm −2, with linear variation of light output with current up to this value.

How to improve light curing output

There are several reasons for low intraoral curing light output as reported in the CRA Newsletter February 1989.l TRCINSFORNER STEPUP Output 126 VAC Fig. 1 illustrates the variation in light output versus line voltage input. The equipment used was a Cure Rite radiometer (EFOS, Williamsville, N. Y.), a Fluke 8921A True RMS voltmeter (John Fluke Mfg. Co., Everett, Wash.), a Visilux curing light (3M, St. Paul, Minn.) and a variable transformer. If low voltage is a problem, a wired small transformer will raise the alternating current line voltage; a 6-volt l-ampere transformer is commonly available (Fig. 2). If, after the wiring as shown is completed, the output is reduced by 6V (114 V), the leads marked x and y should be reversed. The output of the transformer needs to be rated for amperage rating of the curing light. X

A Photomicrodynamic System with a Mechanical Resonator Monolithically Integrated with Laser Diodes on Gallium Arsenide

A cantilever resonant microbeam, laser diodes, and a photodiode have been fabricated on the surface of a gallium arsenide substrate. The microbeam is excited photothermally by light from a laser diode. The vibration is detected with a photodiode as the variation in light output caused by the difference in optical length between the microbeam and another laser diode. A high carrier-to-noise ratio (45 decibels) is achieved with a short (3 micrometers) external cavity length. Such a small distance allows a lensless system, which increases the ease of fabrication. This work could lead to applications in which photomicrodynamic systems are monolithically integrated on a gallium arsenide substrate with surface micromachining technology.

Application of highefficiency light sources

The ever increasing development and marketing of lamps has imposed a greater need upon the lighting designer to understand the different operating characteristics of these various lamps and their application in lighting designs. Luminous efficacy must be treated with great care when used to compare light sources of different types, as it conveys no information about variation of light output with age, colour appearance, colour rendering, mortality or flexibility of control.

ＧａＡｓマイクロマシニングによるレーザ集積化振動子の諸特性

A cantilever resonant microbeam (MB), laser diodes (LD), and a photodiode are fabricated on the surface of a gallium arsenide (GaAs) substrate. The microbeam length, width and thickness are 110 (50), 3.0, and 5μm and the distances from the facet of LD 1 to the side wall of the MB and LD 2 to MB are 3.0 and 30μm. The microbeam is excited photothermally by light from one laser diode (LD 2). With a photodiode, the vibration is detected as the light output variation due to the optical length difference between the microbeam and another laser diode (LD 1). Carrier-to-noise ratio is very high (45 dB) due to an extremely short (3μm) external cavity length. Such small distance allows a lensless system, which makes it easier to fabricate.

High-Power, 790 nm, Eight-Beam AlGaAs Laser Array with a Monitoring Photodiode

A high-power, 790 nm, eight-beam individually addressable AlGaAs laser array on 50 µm centers with a monitoring photodiode has been developed for high-speed data transfer in optical memory systems. The maximum output power of each element is over 80 mW. When eight elements are simultaneously operated at 20 mW in APC (Automatic Power Control) mode using the one-beam monitoring control, the total light output variation is less than 7% at a heatsink temperature between 10 and 50°C.

Ion beam sputtered (SiO_2)x(Si_3N_4)_1−x antireflection coatings on laser facets produced using O_2–N_2 discharges

The chemical composition of a (SiO(2))(x)(Si(3)N(4))(1-x) film produced by ion beam sputtering was precisely controlled by the ratio of O(2) and N(2) flow rates under a discharge current kept constant to within an accuracy of +/-0.05 A. The reproducibility of the refractive index was improved to +/-0.01. This film was applied to form antireflection coatings with extremely low reflectivity on facets of 830-nm AlGaAs double heterostructure lasers. The minimum reflectivity was 6.8 x 10(-5), and a reflectivity of 1 x 10(-4) was achieved reproducibly. Experimental studies show that antireflection coatings are effective for suppressing the interferometric light output variation of composite cavity lasers.

Improvement in Signal-to-Noise Ratio of a Longitudinally Coupled Cavity Laser by Internal Facet Reflectivity Reduction

Improvement in signal-to-noise ratio (SNR) is described for 830 nm AlGaAs double heterostructure lasers longitudinally coupled to a short complex cavity formed by a laser facet and an external mirror separated from the facet by a few micrometers. The SNR degraded by external cavity length (spacing) variation is improved by reducing internal laser facet reflectivity using an anti-reflection coating. A variation ratio, newly defined to evaluate light output variation due to spacing, reaches 1.6 at a reflectivity of 6.8×10-5. The SNR degraded by laser intensity noise is improved to 56 dB by biasing the drive current at an optimum corresponding to the noise valley which appears for lower laser facet reflectivity. The SNR degraded by temperature variation is improved by linear current control, maintaining a maximum value of it from 10 to 45°C.