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.
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.
To improve the performance of GaAs NEA photocathodes, an exponential-doping structure GaAs material has been put forward, in which from the GaAs bulk-to-surface doping concentration is distributed exponentially from high to low. We apply this exponential-doping GaAs structure to the transmission-mode GaAs photocathodes. This sample was grown on the high quality
p-type Be-doped GaAs (100) substrate by MBE. We have calculated the band-bending energy in exponential-doping GaAs emission-layer, and the total band-bending energy is 59 meV which helps to improve the photoexcited electrons movement towards surface for the thin epilayer. The integrated sensitivity of the exponential-doping GaAs photocathode samples reaches 1547uA/lm.
The stability for reflection-mode GaN photocathode has been investigated by monitoring the photocurrent and the
spectral response at room temperature. We watch that the photocurrent of the cathode decays with time in the vacuum
system, and compare the spectral response curves after activation and after degradation. The photocurrent decay
mechanism for reflection-mode NEA GaN photocathode was studied by the surface model ［GaN (Mg) :Cs］:O-Cs. The
reduction of the effective dipole quantity, which is caused by harmful gases, is the key factor of the photocurrent
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 (γ<sub>33</sub>=33.6×10<sup>-12</sup>m/v) and the optimal optic system may lead to better time resolution less than 1ns.