And then I could put a couple of plates and I could raster the beam so that when I am looking here,the beam goes back and forth about 80 times a second.

然后我放了两个感光片,我可以检测到光束所以,当我观察时,电子束以每秒80次的速度来来回回了。

麻省理工公开课 - 固态化学导论课程节选