Light Spread Research Articles

Transparent electrode design for AlGaN deep-ultraviolet light-emitting diodes.

Zinc gallate (ZnGa2O4; ZGO) thin films were employed as the p-type transparent contact layer in deep-ultraviolet AlGaN-based light-emitting diodes (LEDs) to increase light output power. The transmittance of 200-nm-thick ZGO in deep-ultraviolet wavelength (280 nm) was as high as 92.3%. Two different ohmic contact structures, a dot-LED (D-LED; ZGO/dot-ITO/LED) and whole-LED (W-LED; ZGO/ITO/LED), exhibited improved light output power and current spreading compared to a conventional ITO-LED (C-LED). At an injection current of 20 mA, the D-LED and W-LED exhibited 33.7% and 12.3% enhancements in light output power, respectively, compared to the C-LED. The enhanced light output power of the D-LED can be attributed to an improvement in current spreading and enhanced light-extracting efficiency achieved by introducing ZGO/dot-ITO.

Polarization dependent Brillouin frequency shift fluctuation induced by low birefringence in single mode fiber.

The polarization dependent fluctuation of Brillouin frequency shift (BFS) of stimulated Brillouin scattering (SBS) in practical single mode fibers (SMFs) is reported. The phenomenon is actually caused by the interference of the low birefringence in SMF with the SBS spectral polarization spreading of the signal light. The performance of the polarization dependent BFS fluctuation is studied by simulation and confirmed with agreeable experimental results.

Modeling and evaluation of a high-resolution CMOS detector for cone-beam CT of the extremities.

Quantitative assessment of trabecular bone microarchitecture in extremity cone-beam CT (CBCT) would benefit from the high spatial resolution, low electronic noise, and fast scan time provided by complementary metal-oxide semiconductor (CMOS) x-ray detectors. We investigate the performance of CMOS sensors in extremity CBCT, in particular with respect to potential advantages of thin (<0.7mm) scintillators offering higher spatial resolution. A cascaded systems model of a CMOS x-ray detector incorporating the effects of CsI:Tl scintillator thickness was developed. Simulation studies were performed using nominal extremity CBCT acquisition protocols (90kVp, 0.126mAs/projection). A range of scintillator thickness (0.35-0.75mm), pixel size (0.05-0.4mm), focal spot size (0.05-0.7mm), magnification (1.1-2.1), and dose (15-40mGy) was considered. The detectability index was evaluated for both CMOS and a-Si:H flat-panel detector (FPD) configurations for a range of imaging tasks emphasizing spatial frequencies associated with feature size aobj. Experimental validation was performed on a CBCT test bench in the geometry of a compact orthopedic CBCT system (SAD=43.1cm, SDD=56.0cm, matching that of the Carestream OnSight 3D system). The test-bench studies involved a 0.3mm focal spot x-ray source and two CMOS detectors (Dalsa Xineos-3030HR, 0.099mm pixel pitch) - one with the standard CsI:Tl thickness of 0.7mm (C700) and one with a custom 0.4mm thick scintillator (C400). Measurements of modulation transfer function (MTF), detective quantum efficiency (DQE), and CBCT scans of a cadaveric knee (15mGy) were obtained for each detector. Optimal detectability for high-frequency tasks (feature size of ~0.06mm, consistent with the size of trabeculae) was ~4× for the C700 CMOS detector compared to the a-Si:H FPD at nominal system geometry of extremity CBCT. This is due to ~5× lower electronic noise of a CMOS sensor, which enables input quantum-limited imaging at smaller pixel size. Optimal pixel size for high-frequency tasks was <0.1mm for a CMOS, compared to ~0.14mm for an a-Si:H FPD. For this fine pixel pitch, detectability of fine features could be improved by using a thinner scintillator to reduce light spread blur. A 22% increase in detectability of 0.06mm features was found for the C400 configuration compared to C700. An improvement in the frequency at 50% modulation (f50 ) of MTF was measured, increasing from 1.8lp/mm for C700 to 2.5lp/mm for C400. The C400 configuration also achieved equivalent or better DQE as C700 for frequencies above ~2mm-1 . Images of cadaver specimens confirmed improved visualization of trabeculae with the C400 sensor. The small pixel size of CMOS detectors yields improved performance in high-resolution extremity CBCT compared to a-Si:H FPDs, particularly when coupled with a custom 0.4mm thick scintillator. The results indicate that adoption of a CMOS detector in extremity CBCT can benefit applications in quantitative imaging of trabecular microstructure in humans.

A comparative study of scintillator combining methods for flat-panel X-ray image sensors

An X-ray transmission imaging based on scintillation detection method is the most widely used radiation technique particularly in the medical and industrial areas. As the name suggests, scintillation detection uses a scintillator as an intermediate material to convert incoming radiation into visible-light particles. Among different types of scintillators, CsI(Tl) in a columnar configuration is the most popular type used for applications that require an energy less than 150 keV due to its capability in obtaining a high spatial resolution with a reduced light spreading effect. In this study, different methods in combining a scintillator with a light-receiving unit are investigated and their relationships are given in terms of the image quality. Three different methods of combining a scintillator with a light-receiving unit are selected to investigate their performance in X-ray imaging: upward or downward oriented needles structure of CsI(Tl), coating layer deposition around CsI(Tl), and insertion of FOP. A charge-coupled device was chosen to serve as the light-receiving unit for the proposed system. From the result, the difference of needle directions in CsI(Tl) had no significant effects in the X-ray image. In contrast, deposition of the coating material around CsI(Tl) showed 17.3% reduction in the DQE. Insertion of the FOP increased the spatial resolution by 38%, however, it decreased the light yield in the acquired image by 56%. In order to have the maximum scintillation performance in X-ray imaging, not only the reflection material but also the bonding method must be considered when combining the scintillator with the light-receiving unit. In addition, the use of FOP should be carefully decided based on the purpose of X-ray imaging, e.g., image sharpness or SNR.

Simulation study of light transport in laser-processed LYSO:Ce detectors with single-side readout

A tightly focused pulsed laser beam can locally modify the crystal structure inside the bulk of a scintillator. The result is incorporation of so-called optical barriers with a refractive index different from that of the crystal bulk, that can be used to redirect the scintillation light and control the light spread in the detector. We here systematically study the scintillation light transport in detectors fabricated using the laser induced optical barrier technique, and objectively compare their potential performance characteristics with those of the two mainstream detector types: monolithic and mechanically pixelated arrays. Among countless optical barrier patterns, we explore barriers arranged in a pixel-like pattern extending all-the-way or half-way through a 20 mm thick LYSO:Ce crystal. We analyze the performance of the detectors coupled to MPPC arrays, in terms of light response functions, flood maps, line profiles, and light collection efficiency. Our results show that laser-processed detectors with both barrier patterns constitute a new detector category with a behavior between that of the two standard detector types. Results show that when the barrier-crystal interface is smooth, no DOI information can be obtained regardless of barrier refractive index (RI). However, with a rough barrier-crystal interface we can extract multiple levels of DOI. Lower barrier RI results in larger light confinement, leading to better transverse resolution. Furthermore we see that the laser-processed crystals have the potential to increase the light collection efficiency, which could lead to improved energy resolution and potentially better timing resolution due to higher signals. For a laser-processed detector with smooth barrier-crystal interfaces the light collection efficiency is simulated to >42%, and for rough interfaces >73%. The corresponding numbers for a monolithic crystal is 39% with polished surfaces, and 71% with rough surfaces, and for a mechanically pixelated array 35% with polished pixel surfaces and 59% with rough surfaces.

Simulation study of a depth-encoding positron emission tomography detector inserting horizontal-striped glass between crystal layers

This study introduces a depth-encoding positron emission tomography (PET) detector inserting a horizontal-striped glass between the pixilated scintillation crystal layers. This design allows light spreading so that scintillation photons can travel only through the X direction and allows alteration in the light distribution so that it can generate a unique pattern diagram of the two-dimensional (2-D) flood histogram that identifies depth position as well as X-Y position of γ-ray interaction. A Monte Carlo simulation was conducted for the assessment of the depth of interaction (DOI)-PET detector. The traced light distribution for each event was converted into the 2-D flood histogram. Light loss caused by inserting the horizontal-striped glass between the crystal layers was estimated. Applicable weighting factors were examined for each DOI-PET detector. No considerable degradation of light loss was observed. The flood histogram, without overlapping of each crystal position, can be generated for the DOI detector based on each crystal block by inserting the horizontal-striped glass with a thickness of >1 mm and the modified resistive charge division networks with applicable weighting factors. This study demonstrated that the proposed DOI-PET detector can extract the three-dimensional γ-ray interaction position without considerable performance degradations of the PET detector from the 2-D flood histogram.

Modeling Imperfections Boosts Microscope Precision

A theoretical model of light spreading and scattering improves precision of position and size measurements made with an optical microscope by as much as 100 times.

Improved spatial resolution of luminescence images acquired with a silicon line scanning camera

Luminescence imaging is currently being used to provide spatially resolved defect in high volume silicon solar cell production. One option to obtain the high throughput required for on the fly detection is the use a silicon line scan cameras. However, when using a silicon based camera, the spatial resolution is reduced as a result of the weakly absorbed light scattering within the camera's chip. This paper address this issue by applying deconvolution from a measured point spread function. This paper extends the methods for determining the point spread function of a silicon area camera to a line scan camera with charge transfer. The improvement in resolution is quantified in the Fourier domain and in spatial domain on an image of a multicrystalline silicon brick. It is found that light spreading beyond the active sensor area is significant in line scan sensors, but can be corrected for through normalization of the point spread function. The application of this method improves the raw data, allowing effective detection of the spatial resolution of defects in manufacturing.

Impact of loss on the light propagation in 1D optical waveguide array in the presence of Kerr-type nonlinearity

The interplay between radiation loss (diagonal and off-diagonal) and Kerr-type nonlinearity on the light propagation in 1D array of nonlinear dissipative optical waveguides are investigated numerically. Our results show that, at low nonlinear parameters, the diagonal loss only reduces the light intensity in the guides and does not affect the ballistic regime of light spreading. However, for nonlinear parameters above a critical value, the transition from the localized to the ballistic regime can be observed, after certain propagation distance. The study of the interplay between off-diagonal loss term and Kerr type nonlinearity, demonstrates that the results depend mainly to the nonlinear parameter strength. In this case, and for low strength of nonlinearity, the transition from ballistic to diffusive regime is observed after a critical propagation distance, while, spreading from localized to diffusive regime occurs at high nonlinear parameters (above the critical one). In addition, we have examined the impact of the both diagonal and off-diagonal losses in highly nonlinear optical lattices. In this case, by increasing the propagation distance, three different regimes of light spreading (from localized to the ballistic, and then, from ballistic to the diffusive) can be observed. Both critical propagation distances in which these transitions occur increase by the magnitude of the nonlinear parameter, while, decrease by the enhancement of the loss coefficients.

Light propagation in binary kagome ribbons with evolving disorder.

By introducing evolving disorder in the binary kagome ribbons, we study the establishment of diffusive spreading of flat band states characterized by diffractionless propagation in regular periodic ribbons. Our numerical analysis relies on controlling strength and rate of change of disorder during light propagation while tailoring binarism of the kagome ribbons in order to isolate the flat band with the gap from the rest of the ribbon's eigenvalue spectrum and study systematically its influence on diffusion. We show that the flat band plays a dominant role in the establishment of the diffusion for a given strength and rate of change of disorder, whereas the rest of the ribbon's eigenvalue spectrum induces only quantitative differences in the light spreading regimes. Due to the universality of studied phenomena, our findings may be of interest in various disordered physical systems with flat spectral bands, ranging from photonics to ultracold matter systems and plasmonics.

Design of a collimated UV-LED exposure unit based on light spread function method.

A collimated and uniform UV-LED exposure unit (EU) applied in a printed circuit board is investigated by the light spread function (LSF) method. To accurately calculate the source-to-source distance of collimated UV-LED sources and achieve uniform irradiance in the exposure area, we propose a regional maximally flat condition for the LSF. This regional maximally flat condition contains irradiance information from multiple positions in two dimensions. To verify the design results, we built this parameter into optical simulation software and used it in our LSF method calculations. The obtained collimated UV-LED EU results show uniformity and average irradiance values of 98.23% and 43.32 mW/cm2, respectively. Thus, we can conclude that the proposed LSF method is effective for achieving a uniform irradiance distribution.

The uncertainty research of visual positioning in different mediums

In engineering application, there existed deviation when light spreads in different mediums. At the same time miscellaneous medium and random fluctuation may lead to inaccuracy of visual positioning. It explored visual positioning technology in condition of different mediums for binocular camera. Firstly focused on medium material and impurity in real environment, the refractive index formula is derived through binocular visual positioning principle. Then considering deviation when light spreads in different mediums, deductive process of vision positioning is realized according to calculated refractive index. Because cloud model can better describe randomness and fuzziness. It was introduced to deal with problems of random fluctuation in different mediums. Finally simulation was designed to prove the accuracy improvement in different mediums. The result showed that accuracy error had decreased by 66.7% after considering transparent organic mediums. Compared with not knowing refractive index, positioning error had decreased by 49.7%.

Special scattering in photorefractive crystal LiNbO3:Fe

We observe special scattering light by using a simple experimental device and record the dynamic behavior with a camera. A laser beam from an Nd:YAG laser, which is expanded by the spatial filter (SF) and collimated by the lens L1 (f1=300 mm), is focused into a line light through a pair of cylindrical lenses L2, L3 (f2=f3=200 mm) and irradiates the LiNbO3:Fe crystal. On condition that the directions of line beam (f) and c-axis of the crystal are both parallel to the horizontal direction, we observe experimentally that the scattering light spreads gradually in the horizontal direction in the far field as irradiation time goes on. Then the scattering light reaches a steady state after 10 min. The scattering light beam is composed of vertical filaments. When the line beam is horizontal and the c-axis is vertical, the scattering light composed of horizontal filaments firstly appears in the vertical direction. About 30 min later, the scattering light appears and spreads along the horizontal direction to the far field as irradiation time goes on. At this time, the scattering light is also composed of vertical filaments. That is to say, we observe the scattering light whose direction is inconsistent with the c axis of the crystal. We also give the corresponding theoretical explanation to the phenomenon. We suppose that the line beam consists of many close-set thread-like sub-beams, which are vertical to the direction of the line beam. When the line beam irradiates the photorefractive crystal, the sub-beams record the gratings in the crystal according to photorefractive nonlinear effect. The gratings diffract the input beam. The scattering light and the incident beam interfere with each other, thereby recording the new grating. At the same time, the new gratings also diffract the incident beam. It goes full circle. So energy transfers from incident beam to the scattering light beam. The direction of the scattering light beam spreads along the direction of the line beam.

Development of a novel depth-of-interaction encoding method and use of light spreading in a scintillation crystal array with single-ended readout

We designed a depth-of-interaction (DOI) positron emission tomography detector by applying a simple light-spreading method in a single-layer crystal array with a single-ended photosensor. By configuring different reflector patterns along the depth of the crystal, we were able to alter the light distribution of the gamma interaction at each depth. To evaluate the characteristics of the new DOI detector, we simulated the optical photon transport in the crystal array by using DETECT2000. Three different arrays comprising triangular-, square-, and hexagonal-shaped crystals were modeled. The 511-keV gamma-ray interactions were generated for all depths, and flood images were acquired. We confirmed that DOI layers could be distinguished in the obtained images and that the number of DOI layers depends on the number of sides of the polygonal crystals.

Design optimization and performances of an intraoperative positron imaging probe for radioguided cancer surgery

Extent and accuracy of surgical resection is a crucial step in operable tumor therapy. Emergence of promising specific tumor-seeking agents labeled with positron emitters is giving rise to a renewed interest for radioguided surgery using beta probes. Beta detection, due to the particle short range, allows a more sensitive and accurate tumor localization compared to gamma radiotracers. In that context, we are currently developing an intraoperative positron imaging probe using SiPM photosensors to perform tumor localization and post-operative control of the surgical cavity. Because compactness is a key feature when trying to detect positron emitters with high sensitivity in small surgical cavities, we chose to study the simplest detector design based on the use of a very thin organic scintillator coupled to the photosensor. Different designs of the positron imaging probe, including scintillator material and thickness, light spreading window and optical reflector, were investigated with Monte-Carlo simulations and measurements. Their impact on the probe performances were optimized in terms of positron sensitivity, gamma rays background noise contamination, spatial resolution and bias and uniformity. The ability of the probes to detect small radiolabeled tumors was also investigated by simulating different phantom uptake configurations.

The Effect of atmospheric humidity level to the determination of Islamic Fajr/morning prayer time and twilight appearance

Islamic prayer times are based on the astronomical position of the Sun in the sky. One of them is the Fajr prayer. It is marked by some indicators in the morning twilight which is white light spread in the Eastern horizon. However, determining the true time of twilight can be difficult. One of the reasons is the effect of atmospheric humidity to the appearance of morning twilight. The higher the humidity, the redder twilight sky appearance. This paper discusses this effect. It is shown that despite of the same Sun's position, sky color can vary considerably. Observations of various solar dip angle have been made to study this effect. Visibility for different angle can change accordingly. We obtained that the average solar dip for Fajr prayer by morning twilight images was -18°39'29.4".

Response for light scattered in the ocular fundus from double-pass and Hartmann-Shack estimations.

Double-pass (DP) and Hartmann-Shack (HS) are complementary techniques based on reflections of light in the ocular fundus that may be used to estimate the optical properties of the human eye. Under conventional data processing, both of these assessment modes provide information on aberrations. In addition, DP data contain the effects of scattering. In the ocular fundus, this phenomenon may arise from the interaction of light with not only the retina, but also deeper layers up to which certain wavelengths may penetrate. In this work, we estimate the response of the ocular fundus to incident light by fitting the deviations between DP and HS estimations using an exponential model. In measurements with negligible intraocular scattering, such differences may be related to the lateral spreading of light that occurs in the ocular fundus due to the diffusive properties of the media at the working wavelength. The proposed model was applied in young healthy eyes to evaluate the performance of scattering in such a population. Besides giving a parameter with information on the ocular fundus, the model contributes to the understanding of the differences between DP and HS estimations.

Determination of the Nonequilibrium Steady State Emerging from a Defect.

We consider the nonequilibrium time evolution of a translationally invariant state under a Hamiltonian with a localized defect. We discern the situations where a light cone spreads out from the defect and separates the system into regions with macroscopically different properties. We identify the light cone and propose a procedure to obtain a (quasi)stationary state describing the late time dynamics of local observables. As an explicit example, we study the time evolution generated by the Hamiltonian of the transverse-field Ising chain with a local defect that cuts the interaction between two sites (a quench of the boundary conditions alongside a global quench). We solve the dynamics exactly and show that the late time properties can be obtained with the general method proposed.

McGrathMAC versus ProAct illumination during laryngoscopy in a pre‐hospital patient with maxillofacial trauma

SummaryDuring a case of pre‐hospital anaesthesia, the presence of dried oropharyngeal blood from maxillo‐facial trauma was found to adversely affect illumination when using the McGrath® MAC enhanced direct laryngoscope, using both direct laryngoscopy and video‐laryngoscopy via its LCD screen. A second attempt using direct laryngoscopy with a standard battery handle operated laryngoscope (ProAct®Metal Max 100) was noted to provide far superior light quality, intensity and spread. Subsequent comparison of light under basic test conditions demonstrated lower luminance and spread of light with the McGrath® MAC when compared with the standard ProAct® (both with Macintosh size 4 attachments).

Photoluminescence Imaging Using Silicon Line-Scanning Cameras

We experimentally demonstrate photoluminescence imaging using a silicon line-scanning camera. The narrow rectangular geometry of the sensor effectively lowers the image-blur, while keeping the sensitivity relatively high. Line scanning is demonstrated to provide sharp and high contrast images. To maintain fast measurement speeds, higher injections are used to compensate for the lower sensitivity of a line-scan measurement, where localized parts of the image are acquired sequentially. However, low-injection measurements remain possible at the expense of slower scan speeds if cooling is applied to the sensor. Using a detailed point-spread analysis and deconvolution, we quantify and correct for the remaining light spreading effects. Experimental results suggest an effective suppression of the cumulative nonlocal point spread commonly observed using area sensors, confirming silicon (Si) line sensors to be only susceptible to local point spreading effects.