Quantum efficiency enhancement of reflective GaAs photocathodes with exponential-doping structure generating a favorable built-in electric field.

The rapid development of GaAs photocathodes has led to an increased focus on the attainment of high quantum efficiency. Three types of exponential-doping structures with a high to low doping concentration distribution from the interior to the surface are proposed for reflective GaAs emission layers. These three structures generate different built-in electric fields that facilitate photoelectron emission.

Enhanced photovoltaic panel defect detection via adaptive complementary fusion in YOLO-ACF.

Detecting defects on photovoltaic panels using electroluminescence images can significantly enhance the production quality of these panels. Nonetheless, in the process of defect detection, there often arise instances of missed detections and false alarms due to the close resemblance between embedded defect features and the intricate background information. To tackle this challenge, we propose an Adaptive Complementary Fusion (ACF) module designed to intelligently integrate spatial and channel information.

Graphene Intermediate Layer for Robust and Spectrum-Extended Cu Photocathode Activated with Cs and O.

Developing an effective method to stably enhance the quantum efficiency (QE) and extend the photoemission threshold of Cu photocathodes beyond the ultraviolet region could benefit the photoinjector for ultrafast electron source applications. The implementation of a 2D material protective layer is considered a promising approach to extending the operating lifetime of photocathodes. We propose that graphene can serve as an intermediate layer at the interface between photocathode material and low-work-function coating.

Effective method for low-light image enhancement based on the JND and OCTM models.

Low-light images always suffer from dim overall brightness, low contrast, and low dynamic ranges, thus result in image degradation. In this paper, we propose an effective method for low-light image enhancement based on the just-noticeable-difference (JND) and the optimal contrast-tone mapping (OCTM) models. First, the guided filter decomposes the original images into base and detail images.

Effective enhancement method of low-light-level images based on the guided filter and multi-scale fusion.

Aiming to solve the problem of low-light-level (LLL) images with dim overall brightness, uneven gray distribution, and low contrast, in this paper, we propose an effective LLL image enhancement method based on the guided filter and multi-scale fusion for contrast enhancement and detail preservation. First, a base image and detail image(s) are obtained by using the guided filter. After this procedure, the base image is processed by a maximum entropy-based Gamma correction to stretch the gray level distribution.

Dynamic photoelectron transport in stepwise-doped GaAs photocathodes.

We present a theoretical model describing photoelectron transport dynamics in stepwise-doped GaAs photocathodes. Built-in electric field caused by the doping structure is analyzed, and the time-evolution of electron concentration in the active layer induced by a femtosecond laser pulse is solved. The predictions of the model show excellent agreement with the experimental data measured with pump-probe transient reflectometry, demonstrating the capability of the theoretical model in predicting photoelectron behaviors in real devices.

Automatic evaluation of vertex structural defects on the anode surface of a low-light-level image intensifier based on proposed individual image processing strategies.

In the process of microchannel plate (MCP) making and physicochemical treatment of a low-light-level (LLL) image intensifier, multifilament fixed pattern noise, also known as structural defects, is one of the most common defects in the anode surface. The appearance of this defect will seriously affect the imaging quality of an image intensifier, so it should be found in time before delivery. The traditional evaluation method of this defect relies on subjective judgment, and the disadvantage is that the division of the dense defect area and the measurement of defect gray difference (GD) are not standardized.

Defect detection system for silicon solar panels under all-day irradiation.

In terms of the shortcomings of defect detection based on the electroluminescence of conventional silicon solar panels, which can only be performed under darkroom conditions, a defect detection system that can work under the Sun with any irradiance in all weather is designed. The system electrifies solar panels through a modulated current source, uses high frame rate InGaAs area array detectors for image data acquisition, and transmits images via CameraLink. Using these image data as data sources, a defect display algorithm model is designed.

Improved preparation techniques for preparing high-performance GaAs photocathodes.

Efficiency and lifetime are always problems raised with photocathodes during operation. With the purpose of obtaining high-performance GaAs photocathodes with high sensitivity and long operational lifetime, it is necessary to investigate the preparation techniques during both the cleaning and the activation procedure. By comparison with the classical preparation techniques, the improved preparation techniques with an optimized chemical etching method and activation procedure are proposed.

Comparison of photoemission performance of a GaAs photocathode between white light and monochromatic light illumination during activation.

To obtain higher quantum efficiency and longer operational lifetime of negative-electron-affinity GaAs-based photocathodes, illumination conditions using different light sources during the activation process are explored. GaAs photocathodes were activated under white light and 633 nm monochromatic light with different intensities, and experimental quantum efficiencies and photocurrent degradations were compared after activation and recaesiation. The results show that GaAs photocathode can obtain higher quantum efficiency and longer lifetime by using illumination of 633 nm monochromatic light, and this advantage can hardly be achieved by adjusting the intensity of white light.

Improved quantum efficiency and stability of GaAs photocathode using favorable illumination during activation.

Considering that illumination using the light source is required to monitor the activation progress of negative-electron-affinity GaAs-based photocathodes, it is important to understand if and how the illumination affects the activation. To improve the photoemission performance of GaAs photocathode, epitaxial GaAs samples are Cs/O activated and recesiated under illumination of monochromatic light of blue (460 nm), green (532 nm), and red (633 nm) with approximately the same incident photons, and halogen tungsten lamp as white light source, respectively, to induce photoemission. The performance characteristics including quantum efficiency and photocurrent degradation among the samples treated by different illumination conditions are compared to investigate their photoemission capability and stability.

Effect of graded bandgap structure on photoelectric performance of transmission-mode AlGaAs/GaAs photocathode modules.

The graded bandgap AlGaAs/GaAs photocathode with graded composition and exponential doping structure has shown great potential for improving photoemission capability. In order to better study the performance of transmission-mode AlGaAs/GaAs photocathode with the complex graded bandgap structure, the experimental optical properties and quantum efficiency are measured by comparison with uniform composition and exponential doping AlGaAs/GaAs photocathode. The theoretical optical properties of the multilayer AlGaAs/GaAs photocathode modules are calculated by matrix formula on the basis of thin-film optical principles.

Comparison of degradation and recaesiation between GaAs and AlGaAs photocathodes in an unbaked vacuum system.

The lifetime and reliability of a photocathode during operation are always raised problems and the photocathode performance depends on the vacuum condition. With the purpose of investigating the stability and reliability of a GaAs-based photocathode in a harsher vacuum environment, reflection-mode exponential-doped GaAs and AlGaAs photocathodes are metalorganic vapor-phase epitaxial grown and then (Cs, O) activated inside an unbaked vacuum chamber. The degraded photocurrents are compared after activation and recaesiations between GaAs and AlGaAs photocathdoes under illumination with an equal initial photocurrent and an equal optical flux, respectively.

Comparative study of Al(x)Ga(1-x)As/GaAs photocathodes with different aluminum concentrations by surface photovoltage spectroscopy.

The influence of aluminum concentration in an Al(x)Ga(1-x)As window layer on the performance of Al(x)Ga(1-x)As/GaAs photocathodes was investigated. Three types of transmission-mode photocathode materials with different aluminum concentrations were designed for the comparative research. The surface photovoltage technique was applied to prepare samples.

Photoemission from advanced heterostructured Al(x)Ga(1-x)As/GaAs photocathodes under multilevel built-in electric field.

A heterostructured Al(x)Ga(1-x)As/GaAs photocathode consisting of a composition-graded buffer layer and an exponential-doped emission layer is developed to improve the photoemission performance over the wavelength region of interest. The theoretical quantum efficiency models for reflection-mode and transmission-mode Al(x)Ga(1-x)As/GaAs photocathodes are deduced based on one-dimensional continuity equations, respectively. By comparison of simulated results with conventional quantum efficiency models, it is found that the multilevel built-in electric field can effectively improve the quantum efficiency, which is related to the buffer layer parameters and cathode thicknesses.

Resolution properties of transmission-mode exponential-doping Ga0.37Al0.63As photocathodes.

Using the modulation transfer function obtained by establishing and solving the two-dimensional continuity equation, we have calculated and comparatively analyzed the resolution characteristics of transmission-mode exponential-doping and uniform-doping Ga0.37Al0.63As photocathodes.

Resolution characteristics for reflection-mode exponential-doping GaN photocathode.

According to the expression for modulation transfer function obtained by solving the established 2D continuity equation, the resolution characteristics for reflection-mode exponential-doping and uniform-doping GaN photocathodes have been calculated and comparatively analyzed. These calculated results show that the exponential-doping structure can upgrade not only the resolution capability but also the quantum efficiency for a GaN photocathode. The improvement mechanism is different from the approach for high resolution applied by reducing Te and L(D) or increasing S(V), which leads to low quantum efficiency.

Measurement device for noise factor of microchannel plate.

A new method for noise power factor determination of microchannel plates (MCPs) is described in this paper. The new measuring condition and specific measuring instrument are reported. The system consists of a vacuum chamber, an electron gun, a high-voltage supply, an imaging luminance meter, control units, a signal processing circuit, an A/D converter, a D/A converter, a communication unit, an industrial computer, and measurement software.

Comparative research on GaAs photocathodes before and after activation.

Obtaining higher quantum efficiency and more stability has been an important developing direction in the investigation of GaAs photocathodes. By solving the one-dimensional diffusion equation for no-equilibrium minority carriers of reflection-mode GaAs photocathode materials, we can get the equations of the surface photovoltage curve before activation and the spectral response curve after activation for uniform and exponential doping GaAs materials. Through experiments and fitting calculations for two doping structural materials designed by us, the parameters of the body materials are exactly measured by the surface photovoltage curves, and the curves for surface escape probability are also accurately fitted by the comparative research before and after activation.