Research Based On Semiconductor High-speed Photorefractive X-ray Diagnostic Technology

In the study of inertial confinement fusion (ICF) experiments, X-ray diagnosis is an important technology to get the information from high temperature plasma evolution processes, such as electronic temperature, electronic density, temperature gradient, density gradient and plasma opacity. It’s also an improtant way to understand the interaction between laser and material, plasma heating and compression, implosion dynamics and thermonuclear burning and other important processes. Since these processes only last for tens of picoseconds to hundreds of picoseconds, it means that fast time resolution of a few picoseconds will be required for X-ray detection. Especially for indirect driven fusion, according to the latest research report of National Ignition Facility (NIF), the fluid instability in the implosion is the main causes of failure in NIF ignition experiment. Through ultrafast X-ray diagnosis, the fluid instability development information can be gotten. Therefore, the development of ultrafast X-ray diagnostic techniques is of great significance for further understanding some key processes of ICF and finally realizing laser fusion successfully.Among those new X-ray diagnostic techniques developed recent years, one solution measures radiation-induced changes in the optical refractive index of a direct band-gap semiconductor, thus converting the X-ray signals into the optical regime based on optical measurement of refractive index change. This technique has the advantages of high temporal resolution, high dynamic range and resistance to electromagnetic interference. It may reach femtosecond time resolution and a few hundred picoseconds measuring time.After studying the research background and development of the X-ray diagnostic technique, the main content is as follows:1. The research background and development of the X-ray diagnostic technique are summarized. After discussing the significance of X-ray diagnosis and different kinds of X-ray diagnosis technologies in ICF, we further explain the basic principle of the ultrafast all-optical X-ray detector based on semiconductor photorefractive effect.2. A dynamics model and the relevant equations describing the relation between photorefractive effect and carriers are established. A femtosecond pump-probe experiment is carried out to study the nonlinear optical parameters of CdSe, which can also be used for measuring parameters of other semiconductors.3. We study the electron cascades in gallium arsenide (GaAs) and cadmium selenide (CdSe) using Monte Carlo method since the temporal and spatial resolutions are important parameters of the ultrafast X-rays detector. According to the calculations, the energy deposition time and scale of GaAs and CdSe are gotten. Electron cascades don’t have much impact on getting picosecond time resolution and high spatial resolution.4. Chirped pulse used as probe beam is the key technique for the ultrafast all-optical X-ray detector. However, as the chirped parameter of the probe beam is usually not known, we designed an experiment and studied the parameters of chirped pulse using optical Kerr gate technology.5. Based on supercontinuum pulse, we further studied the ultrafast single-shot measurement of optical Kerr effect, which verified the single-shot ability of supercontinuum pulse.6. Finally, the summary of the whole work is given and the prospect of the further study are indicated.