The streak tube with a large effective photocathode area, high spatial resolution, and high temporal resolution are essential for improving the detection accuracy of the streak tube imaging lidar (STIL). In this paper, a three-dimensional streak tube with single-lens focusing system is developed in CST STUDIO SUITE to systematically investigate the dependences of the dynamic spatio-temporal resolution on the geomagnetic fields. The electro-magnetic distribution in streak tube is calculated by adopting discretized Maxwell’s equations and Finite integral method (FIM). Monte Carlo (M-C) sampling is used to determine the initial distribution of electrons in the visible photocathode. The photoelectrons trajectories are tracked by using the particle-in-cell (PIC) method. All simulations are conducted under both shield (no magnetic field applied with the 3D model) and unshielded (49524.5 nT magnetic field applied with the 3D model) conditions. The results show that the shielding structure can significantly reduce the spatial dispersion of streak tube, and greatly improve the spatial resolution. In addition, there is little difference in temporal resolution, with or without a shielded structure.
In this paper, a special high-voltage pulse synchronization system is designed for the framing camera used in the Z-pinch experiment.The system adopts a system architecture that combines a programmable delay module and a high-voltage pulse generation module. The delay module uses a digital delay chip to achieve picosecond delay. The high-voltage pulse generation module uses a Marx pulse circuit combined in series and parallel to generate high-voltage narrow pulse.Technical parameters: pulse amplitude 2.5kv, pulse width 4.03ns, delay range 2s, delay accuracy 500Ps, pulse jitter less than 150ps. It avoids the line loss and waveform distortion caused by the long transmission line of the traditional delay line method, improves the system integration, reduces the volume and weight of the equipment, and is more convenient to deploy and use.
In this paper, a novel X-ray tube, which uses a photocathode as an electron emission source, is first introduced. The X-ray tube with photocathode can use an external light source to control the output of photoelectrons, thereby controlling the characteristics of the emitted X-rays. Compared with the traditional X-ray tube with hot cathode, the X-ray emitted by the photocathode X-ray tube is completely modulated by the external light source. Therefore, X-rays can achieve instant on-off and arbitrary pulse waveform emission, and have extremely high time resolution. The basic characteristics of the photocathode X-ray tube was tested. By using the developed X-ray tube and LED light source, preliminary X-ray communication experiments have been carried out. The results show that the digital signal restoration with a frequency of up to 1MHz can be achieved. Except for X-ray communication, the developed photocathode X-ray tube can also have important applications in many fields such as radiation calibration and scintillator afterglow measurement.
Owing to the characteristics of high frame frequency, large field of view, small size, streak tube with large work area and small size has been the essential component of the streak tube imaging lidar, and has immense potential in the field of aerospace, space exploration and underwater detection. In this paper, streak tube with a large spherically curved photocathode and small size has been modeled and simulated. The static temporal resolution reaches to 633fs when the effective working diameter of photocathode is 28mm, and its magnification of the image is 1.4. The quantitative relationship between the curvature radius and temporal distortion is analyzed, and temporal distortion can be compensated to minimum when curvature radium R=45mm. Guidance is provided for developing a femtosecond streak tube with large work area and small size for 3D imaging lidar.
Depositing a high secondary electron yield (SEY) film on the microchannel plate (MCP) input electrode is supposed to be an effective approach to improve the photoelectron collection efficiency (CE) of photomultiplier tubes based on MCPs (MCP-PMTs). Nevertheless, secondaries promoted by the photoelectrons striking the MCP input face may cause a long tail in the time distribution of the output electrons (TDOE). In our work, laying a conductive grid upon the MCPs is proposed as an effective approach to suppress the tail. A three-dimensional MCP-PMT model is developed in CST STUDIO SUITE to systematically investigate the dependence of the TDOE on the applied voltage (U) of the grid at the coated material SEY=6. Simulation results show that high voltage applied on the grid could suppress the delay pulse effectively. The optimal U is above 500 V.
We report cylinder photon traps, prism photon traps, and SiO2/Ta2O5 antireflection films added to the active areas of short wavelength infrared detectors. The total device thickness was estimated ~3.3μm and with the p-i-n structure based on antimonide. The simulation results show that the photon traps increase the absorption of the invisible spectrum distinctly. Also, the optical measurements reveal that maximal responsivity of the detector with PTs array is 0.094A/W in the visible range and 0.64A/W in the short wavelength infrared spectrum. The responsivity in the wavelength of short-wave infrared can be increased apparently as well. Thus, the photon traps array may a potential method for antimonide-based visible to short wavelength infrared bispectral photodetector.
Cesium iodide (CsI) photocathode is widely used in various UV (ultraviolet) detecting devices because of its high quantum efficiency (QE) and good stability under short exposure to humid air. In this paper, the performance of the opaque CsI photocathode is studied, including imaging performance, influence of humidity on the quantum efficiency and the stability of the CsI photocathode under FUV irradiation. In the experiment, the input surface of the MCP was evenly divided into four parts. Different thicknesses of the CsI photocathode were deposited directly on the front surface of micro-channel plates (opaque photocathode). The response of different thicknesses and the stability of UV quantum efficiency of CsI photocathode under FUV illumination were studied by using UV monochromator. At the same time, the influence of humid air exposure on the quantum efficiency of CsI photocathode was tested. According to the experimental results, a FUV detector (vacuum tube) based on opaque CsI photocathode was fabricated and the quantum efficiency of the detector was tested. Absolute quantum efficiency of the FUV detector is over 15.5% at 121nm.
We report three kinds of surface passivation for AlxInyAsSb APD, which are SiO2, SiO2 after sulfuration and SU8 2005 treatments. A good sidewall profile of mesas were etch by Inductively Coupled Plasma (ICP) to 2.6μm depth. The order of dark current for device with SU8 passivation is less than -12 under the temperature of 100K. Dark current and photocurrent increase linearly with diameter of mesa. Also, the devices with different passivation methods produce photocurrent excited by incident power. The measurements are consistent with CV modeling and electric field simulations.
A small size and long slit streak tube with high spatial resolution was designed and optimized. Curved photocathode and screen were adopted to increase the photocathode working area and spatial resolution. High physical temporal resolution obtained by using a slit accelerating electrode. Deflection sensitivity of the streak tube was improved by adopting two-folded deflection plates. The simulations indicate that the photocathode effective working area can reach 30mm × 5mm. The static spatial resolution is higher than 40lp/mm and 12lp/mm along scanning and slit directions respectively while the physical temporal resolution is higher than 60ps. The magnification is 0.75 and 0.77 in scanning and slit directions. And also, the deflection sensitivity is as high as 37mm/kV. The external dimension of the streak tube are only ∅74mm×231mm. Thus, it can be applied to laser imaging radar system for large field of view and high range precision detection.
Streak tube imaging lidar, as a novel flash lidar, due to its advantages of higher resolution for low contrast conditions, compact and rugged physical configurations, small image distortions owing to its scannerless design, and higher image update rates, has immense potential to provide 3D single-laser-pulse scannerless imaging, 3D multispectral imaging, 3D multispectral fluorescence imaging, and 3D polarimetry. In order to further reduce the size and enlarge the field of view (FOV) of the lidar system, we designed a super small-size, large photocathode area and meshless streak tube with spherical cathode and screen. With the aid of Computer Simulation Technology Software package (CST), a model of the streak tube was built, and its predominant performances were illustrated via tracking electron trajectories. Spatial resolution of the streak tube reaches 20lp/mm over the entire ∅28mm photocathode working area, and its temporal resolution is better than 30ps. Most importantly, the external dimensions of the streak tube are only ∅50mmx100mm. And several prototypes are already manufactured on the basis of the computer design.
The quantum efficiency characteristics of InP/In0.53Ga0.47As/InP photocathode which is one of the field-assisted negative electron affinity photocathodes with III-V compound semiconductor and works at transmission mode with a wide1 spectral response range from 1.0-1.7 μm were studied in this paper. Under certain field-assisted bias voltage, internal quantum efficiency at different wavelength versus structure parameters and doping concentration of the photocathode was simulated by the APSYS program. Results show that: First, internal quantum efficiency of the photocathode rises with the increasing of the field-assisted bias voltage. Second, the internal quantum efficiency gradually increases to a maximum at thickness=0.2um of P-InGaAs photo-absorbing layer and then reduces with the increasing of thickness. However, doping concentration of P-InGaAs photo-absorbing layer has little influence on it. Third, the internal quantum efficiency reduces with the increasing of thickness and doping concentration of P-InP photoelectron-emitting layer. The optimization results show that when the thickness of the photo-absorbing layer and the photoelectron-emitting layer are both 0.2 μm, and the doping concentration of the photo-absorbing layer and the photoelectron-emitting layer are about 1.5×1015 cm-3 and 1.0×1016 cm-3 respectively, under a certain field-assisted bias voltage, the line of the external quantum efficiency versus wavelength is ideal. Besides, the response time of photocathode can be reduced to less than 50 ps.
Highly photo-excited layer thickness in GaAs is measured using a pump probe arrangement. A normally incident pump illumination spatially modulated by a mask will induce a corresponding refractive index change distribution in the depth direction due to edge scattering and attenuation absorption effect, which can deflect the probe beam passing through this excited region. Maximum deflection of the probe beam will be limited by the thickness of excited layer, and thus can also be employed to measure the thickness of the photo-excited layer of the material. Theoretical calculation confirms the experimental results. This method can find its application in measurements of photo-excited layer thickness of many kinds of materials and be significant to study the characteristics of materials in laser machining, grating and waveguide fabricating.
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