Improvement of light collection efficiency of lens-coupled YAG screen TV system for a high-voltage electron microscope

A new lens coupling television (TV) system using a YAG (Yttrium Aluminum Ga rnet: Y3Al5O12: Ce3+) single crystal screen has been developed for a high-v oltage electron microscope (HVEM), and its performance is examined. The sys tem, using a combination of YAG and lenses, is less damaged by high-energy electron irradiation and reduces the influence of X-rays on the image. YAG screens have not been used for lens-coupling systems, because the high refr active index (n = 1.84) of YAG results in a low light collection efficiency for emitted light. This disadvantage is overcome by combining a thin YAG d isk screen (thickness; 100 mu m) with a glass hemisphere whose refractive i ndex is 1.81. We found that the light intensity is almost the same as that obtained with a conventional P22 powder screen and lenses system. The resol ution is about 55 mu m on the YAG screen, and this value is 1.3 times highe r than that measured by the conventional system. Shading and distortion do not affect TV observation. Detection quantum efficiency, obtained after cor rection of the channel mixing effect, is about 0.1. (C) 2000 Wiley-Liss, In c.