Baiyu Liu

A new designed impedance matching circuit used for gated framing camera

Framing camera based on gated Micro-channel plate (MCP) was widely used in inertial confinement fusion (ICF) and Z-pinch because of its ultrafast time-resolve. Electrons with imaging information are multiplied when the HV pulse propagating through the MCP strip line. Obviously, the HV pulse was used as a shutter here, then the exposure time of the imagine will be determined by the width of the pulse. Theoretical analysis indicates that thegating pulse(200ps) has a bandwidth of 5GHz, thus, impedance match in the propagating path of the pulse will be very important. Impedance mismatch will cause reflecting of the pulse and decrease the transmission efficiency. This will cause un-uniformity of the dynamic gain of the MCP, and finally resulting in imagedistortion. A new designed impedance matching circuit is developed in this paper. Simulated results showedthatthe newdesignedimpedance matching circuit couldreduce the reflection of thegating pulse significantly, and dynamicgain uniformity of the MCP was increased simultaneously

A Prototype X-ray Framing Camera With Variable Exposure Time Based on Double-Gated Micro-Channel Plates

We present a novel X-ray frame camera with variable exposure time that is based on double-gated micro-channel plates (MCP). Two MCPs are connected so that their channels form a Chevron-MCP structure, and four parallel micro-strip lines (MSLs) are deposited on each surface of the Chevron-MCP. The MSLs on opposing surfaces of the Chevron-MCP are oriented normal to each other and subjected to high voltage. The MSLs on the input and output surfaces are fed high voltage pulses to form a gating action. In forming two-dimensional images, modifying the width of the gating pulse serves to set exposure times (ranging from ps to ms) and modifying the delay between each gating pulse serves to set capture times. This prototype provides a new tool for high-speed X-ray imaging, and this paper presents both simulations and experimental results obtained with the camera.

Simulating the spatial resolution of the framing camera

The structural models of micro-channel plate (MCP) and fluorescent screen of the framing camera were established. By combining the finite element integration and Monte Carlo method, software Simion and Lorenz were respectively used to simulate the effects of different voltages loaded on the fluorescent screen, different closed distance between fluorescent screen and MCP, and electrode immersion depth at MCP output on the spatial resolution, in order to obtain an axisymmetric distribution curve. Results showed that the closed distance between MCP and fluorescent screen had the largest impact on the framing camera’s spatial resolution. In addition, higher fluorescent screen voltage did not necessarily result in better spatial resolution, as it was influenced by the light-emitting mechanism of the fluorescent screen. At the framing camera’s current closed distance of 0.8mm, a fluorescent screen voltage of 5000V could achieve the best spatial resolution.

The New High-speed Switching Study of Ultra-short Laser Pulse Technology

Ultrafast phenomenon has presented widely in natural phenomenon and scientific and technological research. Therefore, study on ultrafast phenomenon is of great important in many research and technology fields. In recent years, the development and application of ultra-short laser pulse has been covered many areas. It has been developed into a powerful tool used to research ultrafast phenomena. In the implementation process of the ultra-short laser pulses, high-speed switching plays a vital role. The difficulty of high-speed switching design is to make the ultrafast electric pulse load on the both ends of the crystal with minimum distortion and delay. It is very difficult to switch electro-optic crystal at a high frequency in traditional method. In this paper, a new method is designed, which combined the electro-optic crystal and micro-strip line. The crystal is a part of the transmission path and the signal path of the micro-strip line is broadened or narrowed continuously to make the impedance matching to 50 ohm. The good match between pulse signal and the crystal make sure the high frequency switches of the crystal. The amplitude loss is less than 11%, and the delay is less than 1 nanosecond.

Transmission loss in x-ray framing cameras

We present evidence that transmission loss in gated x-ray framing cameras can affect relative gains. Transmission loss is caused by a variety of factors including: incident voltage waveform, matched load, width of Au electrode gap, and so on. The transition electrode in MCP (Micro-channel Plate) is continuous gradual change line, and it has good capability of compensation. When continuous gradual change micro-strip line is designed, dielectric loss tangent is one of transmission loss factors too. The model structure is designed based on the analysis of modeling and simulation techniques and experiment data as well as forecast target. The transmission loss is reduced from 50% to 25%, the transmission efficiency is greatly improved.

Performances of a Solid Streak Camera Based on Conventional CCD with Nanosecond Time Resolution

Imaging systems with high temporal resolution are needed to study rapid physical phenomena ranging from shock waves, including extracorporeal shock waves used for surgery, to diagnostics of laser fusion and fuel injection in internal combustion engines. However, conventional streak cameras use a vacuum tube making thus fragile, cumbersome and expensive. Here we report an CMOS streak camera project consists in reproducing completely this streak camera functionality with a single CMOS chip. By changing the mode of charge transfer of CMOS image sensor, fast photoelectric diagnostics of single point with linear CMOS and high-speed line scanning with array CMOS sensor can be achieved respectively. A fast photoelectric diagnostics system has been designed and fabricated to investigate the feasibility of this method. Finally, the dynamic operation of the sensors is exposed. Measurements show a sample time of 500 ps and a time resolution better than 2 ns.

A circuit used for peak power detecting of the laser pulse

Based on the principle of capacitor pre-charging, an analog pulse stretch circuit is designed for detecting peak power of narrow laser impulse. Experimental test were carried out. And it could achieve regulation accuracy of 5ps, jitter<600ps. Due to the need of different delay ranges during the practical applications, the analog pulse stretch circuit is optimized. It doesn’t only meet the different adjustment ranges, but also maintains high regulation accuracy.

A new x-ray framing camera with picoseconds time resolution

A new method to get a X-ray framing camera with picoseconds time resolution was proposed based on time amplification. Its principle comes from that we use high voltage electrical pulse to get speed dispersion of the photoelectrons pulse first, and then the photoelectrons pulse will be stretched in axial direction by drift area, at the end the photoelectrons pulse after stretched will be framing imaged by a traditional MCP（microchannel plate）gated framing camera. A model of the camera was built according to this method. Time amplification of the system is about 30, and image magnification of the system is about 0.4. Parameters for designing the camera system were presented after theoretical deriving and model simulation. At last, theoretical time resolution and spatial resolution of the camera were given.

Solid-state ultrafast all-optical x-ray imaging sensor enabling picosecond temporal resolution

Here we report an ultrafast x-ray imaging sensor based on optical measurement of the effects of x-ray absorption and electron hole pair creation in a direct band-gap semiconductor. Our results indicate that this technology can be used to provide a new approach for x-ray detectors and x-ray imaging systems with picosecond temporal resolution at x-ray energies ~10 keV. The x-ray absorption in GaAs produces a transient, non-equilibrium, electron-hole pair distribution which is then sensed by the phase modulation of the optical probe beam. The basic physics of the detector, implementation considerations, and preliminary experimental data are presented and discussed. Through further development, this x-ray imaging sensor could provide insight into previously unmeasurable phenomena in many fields.

Research on the method of fast photoelectric diagnostics based on ordinary CCD

A novel method to realize fast photoelectric diagnostics using ordinary CCD is presented. By changing the mode of charge transfer of CCD, fast photoelectric diagnostics of single point with linear CCD and high-speed line scanning with array CCD can be achieved respectively. A fast photoelectric diagnostics system of single point based on linear CCD has been designed and fabricated to investigate the feasibility of this method. A pulsed blue light emitting diode (LED) has been used to measure the system. As a proof of concept, the rate of photoelectric diagnostics of single point reachs up to 20 MHz. The results demonstrated that the method of fast photoelectric diagnostics based on ordinary CCD is feasible.