Illumination Positions Research Articles

Lens-free reflective topography for high-resolution wafer inspection

The demand for high-resolution and large-area imaging systems for non-destructive wafer inspection has grown owing to the increasing complexity and extremely fine nature of semiconductor processes. Several studies have focused on developing high-resolution imaging systems; however, they were limited by the tradeoff between image resolution and field of view. Hence, computational imaging has arisen as an alternative method to conventional optical imaging, aimed at enhancing the aforementioned parameters. This study proposes a method for improving the resolution and field of view of an image in a lens-less reflection-type system. Our method was verified by computationally restoring the final image from diffraction images measured at various illumination positions using a visible light source. We introduced speckle illumination to expand the numerical aperture of the entire system, simultaneously improving image resolution and field of view. The image reconstruction process was accelerated by employing a convolutional neural network. Using the reconstructed phase images, we implemented high-resolution topography and demonstrated its applicability in wafer surface inspection. Furthermore, we demonstrated an ideal diffraction-limited spatial resolution of 1.7 μm over a field of view of 1.8 × 1.8 mm2 for the topographic imaging of targets with various surface roughness. The proposed approach is suitable for applications that simultaneously require high throughput and resolution, such as wafer-wide integrated metrology, owing to its compact design, cost-effectiveness, and mechanical robustness.

Mechanistic insights into different illumination positions control algae production in anaerobic dynamic membrane filtration (AnDM) during decentralized wastewater treatment

Sunlight illumination has the potential to control the stability and sustainability of dynamic membrane (DM) systems. In this study, an up-flow anaerobic sludge blanket (UASB) reactor was combined with DM under different illumination positions (direct, indirect and no illumination) to treat wastewater. Results indicated that the UASB achieved a COD removal up to 87.05 % with an average methane production of 0.28 L/d. Following treatment by the UASB, it was found that under illumination, the removal of organic substances by DM exhibited poor performance due to algal proliferation. However, the DM systems demonstrated efficient removal of ammonia nitrogen, ranging from 96.21 % to 97.67 % after stabilization. Total phosphorus removal was 45.72 %, and membrane flux remained stable when directly illuminated. Conversely, the DM system subjected to indirect illumination showed unstable membrane flux and severe fouling resistance. These findings offer valuable insights into optimizing illumination positions in DM systems under anaerobic conditions.

Transition Metal Doped BiVO4 Photoanodes: A Mechanistic Study

BiVO4 has emerged as one of the most promising materials to fabricate efficient photoanodes for photoelectrochemical (PEC) solar water splitting. BiVO4 is an n-type semiconductor, with a 2.4 eV bandgap and a theoretical solar to hydrogen (STH) efficiency of 9.2% with a maximum photocurrent of 7.5 mA cm2 under AM 1.5 G illumination, low overpotential and favourable band-edge positions towards the Oxygen Evolution Reaction (OER).1 However, BiVO4 also presents poor electron transport, high surface recombination and slow water oxidation kinetics. Hence, enormous efforts have been made in the past few years to mitigate these drawbacks through different approaches such as nanostructuring,2 doping,3 heterostructuring,4 and the use of efficient co-catalysts.5 The present study proposes a transition metal doping (Ni, Fe and Co) of BiVO4 photoelectrodes that boosts their water oxidation performance. The origin of this enhanced performance towards Oxygen Evolution Reaction (OER) was studied by a combination of a suite of structural, chemical, and mechanistic advanced characterization techniques including X-Ray Photocurrent Spectroscopy, Electrochemical Impedance Spectroscopy and Transient Absorption Spectroscopy, among others.[1] J. Li and N. Wu, Catal. Sci. Technol., 2015, 5, 1360–1384.[2] S. P. Berglund, D. W. Flaherty, N. T. Hahn, A. J. Bard and C. B. Mullins, J. Phys. Chem. C, 2011, 115, 3794–3802.[3] S. K. Pilli, T. E. Furtak, L. D. Brown, T. G. Deutsch, J. A. Turner and A. M. Herring, Energy Environ. Sci., 2011, 4, 5028–5034.[4] J. Su, L. Guo, N. Bao and C. A. Grimes, Nano Lett., 2011, 11, 1928–1933.[5] D. K. Lee and K.-S. Choi, Nat. Energy, 2018, 3, 53–60.

Material recognition for construction quality monitoring using deep learning methods

Purpose This paper aims to propose a new deep learning technique to detect the type of material to improve automated construction quality monitoring. Design/methodology/approach A new data augmentation approach that has improved the model robustness against different illumination conditions and overfitting is proposed. This study uses data augmentation at test time and adds outlier samples to training set to prevent over-fitted network training. For data augmentation at test time, five segments are extracted from each sample image and fed to the network. For these images, the network outputting average values is used as the final prediction. Then, the proposed approach is evaluated on multiple deep networks used as material classifiers. The fully connected layers are removed from the end of the networks, and only convolutional layers are retained. Findings The proposed method is evaluated on recognizing 11 types of building materials which include 1,231 images taken from several construction sites. Each image resolution is 4,000 × 3,000. The images are captured with different illumination and camera positions. Different illumination conditions lead to trained networks that are more robust against various environmental conditions. Using VGG16 model, an accuracy of 97.35% is achieved outperforming existing approaches. Practical implications It is believed that the proposed method presents a new and robust tool for detecting and classifying different material types. The automated detection of material will aid to monitor the quality and see whether the right type of material has been used in the project based on contract specifications. In addition, the proposed model can be used as a guideline for performing quality control (QC) in construction projects based on project quality plan. It can also be used as an input for automated progress monitoring because the material type detection will provide a critical input for object detection. Originality/value Several studies have been conducted to perform quality management, but there are some issues that need to be addressed. In most previous studies, a very limited number of material types were examined. In addition, although some studies have reported high accuracy to detect material types (Bunrit et al., 2020), their accuracy is dramatically reduced when they are used to detect materials with similar texture and color. In this research, the authors propose a new method to solve the mentioned shortcomings.

Non-line-of-sight snapshots and background mapping with an active corner camera

The ability to form reconstructions beyond line-of-sight view could be transformative in a variety of fields, including search and rescue, autonomous vehicle navigation, and reconnaissance. Most existing active non-line-of-sight (NLOS) imaging methods use data collection steps in which a pulsed laser is directed at several points on a relay surface, one at a time. The prevailing approaches include raster scanning of a rectangular grid on a vertical wall opposite the volume of interest to generate a collection of confocal measurements. These and a recent method that uses a horizontal relay surface are inherently limited by the need for laser scanning. Methods that avoid laser scanning to operate in a snapshot mode are limited to treating the hidden scene of interest as one or two point targets. In this work, based on more complete optical response modeling yet still without multiple illumination positions, we demonstrate accurate reconstructions of foreground objects while also introducing the capability of mapping the stationary scenery behind moving objects. The ability to count, localize, and characterize the sizes of hidden objects, combined with mapping of the stationary hidden scene, could greatly improve indoor situational awareness in a variety of applications.

Single Camera Face Position-Invariant Driver's Gaze Zone Classifier Based on Frame-Sequence Recognition Using 3D Convolutional Neural Networks.

Estimating the driver’s gaze in a natural real-world setting can be problematic for different challenging scenario conditions. For example, faces will undergo facial occlusions, illumination, or various face positions while driving. In this effort, we aim to reduce misclassifications in driving situations when the driver has different face distances regarding the camera. Three-dimensional Convolutional Neural Networks (CNN) models can make a spatio-temporal driver’s representation that extracts features encoded in multiple adjacent frames that can describe motions. This characteristic may help ease the deficiencies of a per-frame recognition system due to the lack of context information. For example, the front, navigator, right window, left window, back mirror, and speed meter are part of the known common areas to be checked by drivers. Based on this, we implement and evaluate a model that is able to detect the head direction toward these regions having various distances from the camera. In our evaluation, the 2D CNN model had a mean average recall of 74.96% across the three models, whereas the 3D CNN model had a mean average recall of 87.02%. This result show that our proposed 3D CNN-based approach outperforms a 2D CNN per-frame recognition approach in driving situations when the driver’s face has different distances from the camera.

Lightweight Bilateral Convolutional Neural Networks for Interactive Single-Bounce Diffuse Indirect Illumination.

Physically correct, noise-free global illumination is crucial in physically-based rendering, but often takes a long time to compute. Recent approaches have exploited sparse sampling and filtering to accelerate this process but still cannot achieve interactive performance. It is partly due to the time-consuming ray sampling even at 1 sample per pixel, and partly because of the complexity of deep neural networks. To address this problem, we propose a novel method to generate plausible single-bounce indirect illumination for dynamic scenes in interactive framerates. In our method, we first compute direct illumination and then use a lightweight neural network to predict screen space indirect illumination. Our neural network is designed explicitly with bilateral convolution layers and takes only essential information as input (direct illumination, surface normals, and 3D positions). Also, our network maintains the coherence between adjacent image frames efficiently without heavy recurrent connections. Compared to state-of-the-art works, our method produces single-bounce indirect illumination of dynamic scenes with higher quality and better temporal coherence and runs at interactive framerates.

Near, far, wherever you are: simulations on the dose efficiency of holographic and ptychographic coherent imaging.

Different studies in X-ray microscopy have arrived at conflicting conclusions about the dose efficiency of imaging modes involving the recording of intensity distributions in the near (Fresnel regime) or far (Fraunhofer regime) field downstream of a specimen. A numerical study is presented on the dose efficiency of near-field holography, near-field ptychography and far-field ptychography, where ptychography involves multiple overlapping finite-sized illumination positions. Unlike what has been reported for coherent diffraction imaging, which involves recording a single far-field diffraction pattern, it is found that all three methods offer similar image quality when using the same fluence on the specimen, with far-field ptychography offering slightly better spatial resolution and a lower mean error. These results support the concept that (if the experiment and image reconstruction are done properly) the sample can be near or far; wherever you are, photon fluence on the specimen sets one limit to spatial resolution.

P6595The optogenetic defibrillation of ventricular arrhythmia in myocardial infarction rats in vivo

Abstract Introduction Optogenetics is a low-invasive, flexible and highly selective intervention that enables electrical excitation with light on myocardium overexpressing light-sensitive proteins. Optical illumination can control the simultaneous exciting of the whole myocardium under the spot, which is more conducive to recovery from electrical disturbance to sinus rhythm. Purpose We explored optogenetic defibrillation for different illumination parameters how to affect defibrillation rates and the possible mechanism of continuous illumination defibrillation. Methods Systemic delivery via right jugular vein injection of (AAV9-CAG-hChR2(H134R)-mCherry) were performed in juvenile SD rats to achieve the light sensitive protein Channelrhodopsin-2 (ChR2) transfer throughout the whole heart. We intubated and ventilated rats, opened chest and recorded the ECG. After ligation of the left anterior descending coronary artery, ventricular arrhythmia was induced by electrical burst stimulation (10v, 50Hz, 2s). Cardiac epicardium illumination with 470nm blue laser was performed to investigate the effects of optogenetic defibrillation and its underlying mechanism. Every heart accepted 30 pulses of 20ms duration on 8Hz to test the light intensity threshold for 1:1 capture. Different illumination modes of multiple light intensity (2,4,8,10,20 times threshold intensity), pulse duration (20, 50, 200, 500 and 1000ms) and illumination position (RV apex, RV, RVOT, septum, LV) were applied in each attempt for 4 repetitions with 1 s interval. Results We demonstrated that ventricular arrhythmias could be terminated by illumination of the right ventricle at 20 times threshold intensity in 1s (figure A) with the successful defibrillation rate of 95±2.673% (mean ±SEM; N=7). Herein, the successful optogenetic defibrillation rate was strongly depending on light intensity (N=5, n=50 episodes, p=0.0118) and duration of illumination (N=5, n=50 episodes, p<0.0001) (figure B.C). Notably when there were higher intensity and longer pulse duration, the higher defibrillation rate appeared. There was no significant difference in the defibrillation rate among different illumination positions (N=5, n=25episodes per position, p=0.1177) (figure D). To explore the underlying mechanism of optogenetic defibrillation, we performed the same illumination mode during sinus rhythm in 2 rats (figure E. F. G). We observed that higher light intensity and longer pulse duration were more conducive to induce an episode of higher frequency focal excitement. Views of optogenetic defibrillation Conclusions We demonstrated that optogenetic defibrillation is a highly effective intervention and the possible mechanism is partly attributed to overdrive suppression. We believe that optogenetic approach is potentially to be translated into more efficient and pain-free clinical termination of ventricular arrhythmia. Acknowledgement/Funding The national natural science foundation of China (81772044)

Investigation and modeling of photocurrent collection process in multiple quantum well solar cells

Solar cells employing quantum wells can enhance the light absorption but suffer from the difficulty in photocarrier extraction. Here, we analyzed the spectral response and the photocarrier collection mechanism of p-i-n multiple quantum well (MQW) solar cells using the effective-mobility model. Both the simulation and experimental results imply that the spatial profiles of electron and hole densities in MQWs play an important role in the carrier collection process. By considering the recombination increment under illumination, our findings suggest that the concept of the majority/minority carriers is important even in the intrinsic region: photogenerated electrons and holes only experience significant recombination when passing through the hole-rich and electron-rich regions, respectively. This can accurately explain the photocurrent behavior in cells with background doping, background illumination, and different MQW positions. Based on the experimental findings, we derived analytical formulae for carrier collection efficiency, which directly show the impact of each cell parameter and can be used for the systematic cell design.

Highly photoresponsive, ZnO nanorod-based photodetector for operation in the visible spectral range

While significant advances have been made for gold nanoparticle (AuNP)-coupled zinc oxide (ZnO) as visibly blind, ultraviolet photodetection devices, very few ZnO nanomaterial systems have been developed specifically for use in the visible wavelength regime. Further efforts to develop ZnO-based visible photodetectors (PDs) are still highly warranted in order to better understand the precise effect of AuNP load, operation wavelength, and beam position on the device output. In this study, we demonstrate significantly enhanced, photoresponse behaviors of AuNP-coupled ZnO nanorod (NR) network devices in the visible wavelength range with their photoresponse capacity comparable to, if not far exceeding, most commercial PDs as well as recently reported, visible, AuNP-coupled ZnO detectors. In addition, the nature and degree of the photoresponsivity enhancement are systematically elucidated by investigating their light-triggered electrical signals under varying incident wavelengths, AuNP amounts, and illumination positions. We discuss a possible photoconduction mechanism of our AuNP-coupled ZnO NR PDs and the origins of the high photoresponsivity. Specifically related to the AuNP amount-dependent photoresponse behaviors, the nanoparticle density yielding photoresponse maxima is explained as the interplay between localized surface plasmon resonance, plasmonic heating, and scattering in our photothermoelectric effect-driven device. We show that the AuNP-coupled ZnO NR PDs can be constructed via a straightforward method without the need for ultrahigh vacuum, sputtering procedures, or photo/electron-beam lithographic tools. Hence, the approach demonstrated in this study may serve as a convenient and viable means to advance the current state of ZnO-based PDs for operation in the visible spectral range with greatly increased photoresponsivity.

Strain distribution in single, suspended germanium nanowires studied using nanofocused x-rays

Within the quest for direct band-gap group IV materials, strain engineering in germanium is one promising route. We present a study of the strain distribution in single, suspended germanium nanowires using nanofocused synchrotron radiation. Evaluating the probed Bragg reflection for different illumination positions along the nanowire length results in corresponding strain components as well as the nanowire's tilting and bending. By using these findings we determined the complete strain state with the help of finite element modelling. The resulting information provides us with the possibility of evaluating the validity of the strain investigations following from Raman scattering experiments which are based on the assumption of purely uniaxial strain.

Light path-length distributions within the retina

A Monte Carlo simulation of light propagation through the retina has been developed to understand the path-length distributions within the retinal vessel. For full-field illumination, the path-length distribution within the vessel comprises directly backscattered light and light that has passed once or twice through the vessel. The origins of these light path-length distributions can be better understood by investigating different combinations of single-point illumination and detection positions. Perhaps the most significant observation is that illumination at the edges of the vessel, rather than over the whole field of view, and detection directly above the vessel capture only the light that has taken a single pass through the vessel. This path-length distribution is tightly constrained around the diameter of the vessel and can potentially provide enhancements for oxygen saturation imaging. The method could be practically implemented using an offset-pinhole confocal imaging system or structured light illumination.

Influence of low resolution of images on reliability of face detection and recognition

In this paper we analyze reliability of the real-time system for face detection and recognition from low-resolution images, e.g., from video monitoring images. First, we briefly describe main features of the standards for biometric face images. Available scientific databases have been checked for compliance with these biometric standards. During the research we have considered both the correctness of extraction (location) of the face from the image as well as the correctness of the identification (based on the eigenfaces approach). To the tests we have used the face databases that allow to study tolerance to illumination and face positions. We have compared various face detection techniques and analyzed minimum requirements for the resolution of facial images. Finally, an influence of the resolution reduction on the FAR/FRR of the recognition is presented.

A gradient-based method for quantitative photoacoustic tomography using the radiative transfer equation

Quantitative photoacoustic tomography (QPAT) offers the possibility of high-resolution molecular imaging by quantifying molecular concentrations in biological tissue. QPAT comprises two inverse problems: (1) the construction of a photoacoustic image from surface measurements of photoacoustic wave pulses over time, and (2) the determination of the optical properties of the imaged region. The first is a well-studied area for which a number of solution methods are available, while the second is, in general, a nonlinear, ill-posed inverse problem. Model-based inversion techniques to solve (2) are usually based on the diffusion approximation to the radiative transfer equation (RTE) and typically assume the acoustic inversion step has been solved exactly. Here, neither simplification is made: the full RTE is used to model the light propagation, and the acoustic propagation and image reconstruction are included in the simulations of measured data. Since Hessian- and Jacobian-based minimizations are computationally expensive for the large data sets typically encountered in QPAT, gradient-based minimization schemes provide a practical alternative. The acoustic pressure time series were simulated using a k-space, pseudo-spectral time domain model, and a time-reversal reconstruction algorithm was used to form a set of photoacoustic images corresponding to four illumination positions. A regularized, adjoint-assisted gradient inversion using a finite element model of the RTE was then used to determine the optical absorption and scattering coefficients.

激光辐照绝缘样品不同位置的沿面闪络性能

激光辐照绝缘样品不同位置的沿面闪络性能

Augmented Small-Scale Database to Improve the Performance of Eigenface Recognition Technique

Eigenface recognition technique reserves limitations in achieving good performance. This includes the large-scale database required, its sensitivity to improper illumination, as well as to different expressions of a human face, and image background. This paper presents an efficient and accessible solution for some of these limitations by improving the database’s design. Face recognition accuracy has been enhanced via the inclusion of a modified version of the images in the database. Illumination and various face positions have been integrated into the already available small-scale database. Recognition is sensitive to the illuminated side of a face under consideration. Applying the proposed approach and choosing proper pre-processing values, has improved the system’s performance.

Effect of UV illumination on surface flashover characteristics of epoxy resin under pulse

Surface flashover in vacuum is a primary limitation to pulsed-power devices. Recently, there are more studies on the pulsed vacuum surface flashover focused on the flashover mechanism. In this paper, the UV illumination is used to study the mechanism of vacuum surface flashover. The effects of different illumination positions, different illumination durations and different illumination intensities are investigated. The results show that the pulsed vacuum surface flashover characteristic is affected by the UV illumination significantly. When the UV light illuminates the cathode triple-point junction, the flashover voltage is reduced; this reduction is almost unaffected by the illumination duration, but significantly increased with the enhancement of illumination intensity. When the UV light illuminates the sample surface, the flashover voltage reduction is increased both by the increases of illumination duration and illumination intensity. Moreover, UV illumination can also change the surface potential and thus influence the surface flashover characteristic.

Laser induced photovoltages in B-riched MgB 2 thin films

Ultrafast photoelectric effects have been observed in MgB 2 thin films fabricated by chemical vapor deposition on MgO (1 1 1) substrates. The rise time and full width at half-maximum of the photoresponse pulse signals were about 2.4 and 4 ns under the irradiation of a 248 nm laser pulse of 20 ns in duration through the MgO substrate at ambient temperature without any bias. Furthermore, the signal polarity is directly bound up with the laser illumination positions, while no photovoltage was observed when the MgO (1 1 1) single crystal was irradiated. The inner origin mechanism of the present positions-dependent photovoltaic response was discussed.

Influence of thick crystal effects on ptychographic image reconstruction with moveable illumination

The properties of the iterative phase-retrieval ptychographical imaging technique are modelled. We use the multi-slice method to generate a series of diffraction patterns when a small convergent illumination spot is moved across a silicon crystal orientated in the 〈1 0 0〉 direction. These are then used to reconstruct the transmission function of the sample by solving the phase of diffraction patterns using the ptychographical iterative engine (PIE) algorithm [H.M.L. Faulkner, J.M. Rodenburg, Physical Review Letters 93 (2004) 023903], which assumes the object is a thin, two-dimensional grating. It is found that to obtain lattice-resolved reconstructions, the thickness of the crystal should be smaller than half of the corresponding extinction distance, the probe should be highly defocused to obtain a planar enough wave front and the movements of the probe should be as small as possible to minimize the changes in the transmission function of the sample for two adjacent illumination positions