Like laser pens have high requirements of the device is generally not used. But! Everything has an exception. This is Spring8 FEL, niubable Japanese with high frequency electronic deflection part need not fall, the rest of the nanosecond level length of beam, and then down to the hard compression, also they could have femtosecond level. In light of the cathode, but as a user device, stable and long time to provide high current beam is the most important, so they give up the photocathode.
Because of the hot cathode bunch length is difficult, so after the laser pens invention, soon in electron. Because the length of the laser is easier to achieve fast, so produced by laser beam is short beam, good control.
A metal cathode, in response to UV laser pens, is the goddess of love Nanuo award reference experiment. Long life of metal cathode, emission of live together. Of course is worse. The specific heat cathode 266nm laser. After all, remove the transition energy of the electron temperature did more than 0.4eV.
And the metal cathode efficiency is very low, generally 10000 photons will hit 1 electrons, do well, barely able to 1000 photon is an electron. So when the high current to play silly, don’t say bad high power UV laser pens is done, playing in the metal, the metal must be broken.