Abstract
The electron microscope has been widely used in many fields. It is a very useful tool to search the microworld. Unfortunately, it is only used to investigate static state because of the limitation of the low brightness of an electron beam. In this paper, we suggest equipping an electron microscope with a laser driven photocathode and making it operate in both cw and the pulsed states. The brightness and coherence of an electron beam from a photocathode are as perfect as those from a field emission gun, but a photocaathode can operate under short-pulse conditions. These advantages are not possessed by field emission and thermionic emission guns. As for the photocathode materials, many experiments have proved that the photocathodes made of semiconductors may have higher current densities and lower divenrgences. Now the laser to be used to drive a photocathode is Nd:YAG; this laser can work in both cw and pulsed states. In this way, under the cw operation, it is very convenient to align, and under the pulse operation, it is used to make pulse electron holograms.
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