Fundamental Study on a High Brightness and High Resolution YAG Screen for Electron Microscopy

在一种新的电子显微镜电视系统中，用一种带光电阴极的透镜光学系统耦合，用单晶的石榴石作闪烁体，将电子图像转换成光图像。透镜耦合YAG闪烁体系统具有克服高能电子辐照损伤和降低X射线对比度的优点。然而，由于高折射率的激光晶体将大部分发射的光反射到晶体的真空界面上，因此用这种系统很难同时达到高亮度和高分辨率。为了克服这种全反射问题，我们研制了一种新型的片状YAG晶体和玻璃半球相结合的闪烁体，并设计了新的透镜光学系统。[第一年]：1.研制了新型的YAG晶体，用于100千伏电子显微镜的半球体和用于1000千伏电子显微镜的片状晶体和玻璃半球的组合。设计了一套用于1000kV电子显微镜的透镜耦合光学系统。[第二年]；1将新型的YAG闪烁体与带坐式电视管的透镜光学系统相结合，研制了一种用于高压电子显微镜的新型电视系统。我们用光源和1000千伏的电子显微镜对其特性进行了评价：(1)分辨率为50-60微米。在适当的聚焦条件下，由于半球引起的像平面的曲率可以减小。(2)亮度玻璃半球使亮度提高了3倍。(3)在电视屏幕的边缘，由于半球引起的失真为-4%。(4)在监视器周围区域的减小不会影响监视器的70%以上，这是不可能的。(5)DQE 0.04-0.12。我们证明了抗电子辐照损伤和X射线效应的高压电子显微镜电视系统是可行的。

Coupled by a lens optical system with a photo-cathode, a single crystal of YAG (Yttrium Aluminum Garnet) has been used for a scintillator, which exchanges electron images to light images, in a new TV system for an electron microscopy. Lens coupled YAG scintillator system has advantages for damages due to the high energy electron irradiation and for lowering contrast by the x-ray. It was difficult, however, to achieve both high brightness and high resolution with this system, because the high refractive index of YAG reflects most of the light emitted in the crystal at the YAG-vacuum interface. In order to over come this problem of total reflection, we have developed a new scintillator combined a platelet YAG crystal with a glass hemisphere and have designed newly lens optical system.[In the first year] ;1. New type YAG scientillators have been developed, a hemisphere YAG crystal for a 100 kV electron microscope and a combination of platelet YAG and a glass hemisphere for a 1000 kV electron microscope.2. A lens coupling optical system for the 1000 kV electron microscope has been designed.[In the second year] ;1 Combining the new YAG scintillator and the lens optical system with a SIT-type TV-tube, we have produced a new TV system for the high voltage electron microscope, and2. We evaluated its characteristics with a light source and the 1000 kV electron microscope as,(1) Resolution The resolution is 50-60 mum on YAG for 1000 kV electrons.The curvature of a image plane due to the hemisphere can be reduced with a proper focusing condition(2) Brightness The glass hemisphere improves the brightness by a factor of 3.(3) Distortion The distortion due to the hemisphere is -4% at the edge of the TV screen.(4) Diminishing in the surrounding area dose not affect more than 70% in the monitor, and it is improbable.(5) DQE 0.04-0.12Consequently, we demonstrated that the TV-system for HVEM which is resistant to an electron irradiation damage and the effect of x-ray is available.