Wenzheng Yang

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.

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.

Three-dimensional reconstruction of laser-imploded targets from simulated pinhole images

This paper proposes an integral method to achieve a more accurate weighting matrix that makes very positive contributions to the image reconstruction in inertial confinement fusion research. Standard algebraic reconstruction techniques with a positivity constraint included are utilized. The final normalized mean-square error between the simulated and reconstructed projection images is 0.000365%, which is a nearly perfect result, indicating that the weighting matrix is very important. Compared with the error between the simulated and reconstructed phantoms, which is 2.35%, it seems that the improvement of the accuracy of the projection image does not mean the improvement of the phantom. The proposed method can reconstruct a simulated laser-imploded target consisting of 100×100×100 voxels.

Improvement methods of reflective photocathode QE of X-ray frame camera

Time-resolved diagnosis of the transient process using X-ray frame cameras (XRCs) is an important means in inertial confinement fusion (ICF) experiments. The sensitivity of the photocathode is a key parameter of the entire camera system. This letter aims to raise the quantum efficiency (QE) of the photocathode. With the changes in the deposition parameters, such as deposit angle, thickness of the coating in the channel, and vacuum of evaporation, the QE results are different. After testing and theoretical calculation, we find that there is a best matching value among these parameters. When the coating parameter meet this best value, the gain of the XRC can be improved significantly.

Research on a solid state-streak camera based on an electro-optic crystal

With excellent temporal resolution ranging from nanosecond to sub-picoseconds, a streak camera is widely utilized in measuring ultrafast light phenomena, such as detecting synchrotron radiation, examining inertial confinement fusion target, and making measurements of laser-induced discharge. In combination with appropriate optics or spectroscope, the streak camera delivers intensity vs. position (or wavelength) information on the ultrafast process. The current streak camera is based on a sweep electric pulse and an image converting tube with a wavelength-sensitive photocathode ranging from the x-ray to near infrared region. This kind of streak camera is comparatively costly and complex. This paper describes the design and performance of a new-style streak camera based on an electro-optic crystal with large electro-optic coefficient. Crystal streak camera accomplishes the goal of time resolution by direct photon beam deflection using the electro-optic effect which can replace the current streak camera from the visible to near infrared region. After computer-aided simulation, we design a crystal streak camera which has the potential of time resolution between 1ns and 10ns.Some further improvements in sweep electric circuits, a crystal with a larger electro-optic coefficient, for example LN (γ33=33.6×10-12m/v) and the optimal optic system may lead to better time resolution less than 1ns.