Apparatus and method for providing a modulated electron beam

Claim 1

An electron gun for emitting a modulated high power electron beam comprising: an evacuated envelope having an output end; a photocathode disposed in said envelope for emitting electrons in response to the exposure to light; an anode positioned between said photocathode and said output end for accelerating electrons emitted by said photocathode; potential means interconnected between said anode and said photocathode for maintaining said anode electrostatically positive relative to said photocathode; a first laser providing a first laser beam at a first frequency illuminating said photocathode, and a second laser providing a second laser beam at a second frequency illuminating said photocathode at the same time, said first frequency differing from said second frequency by a beat frequency, whereby said photocathode provides said electron beam of electrons in which the electrons are spatially bunched in accordance with said beat frequency, said anode being annular and having a central aperture for passing said electron beam, said anode including an electrically conductive mesh screen positioned over said aperture, said beat frequency being between 50 MHz and 100 GHz, the spacing between said photocathode and said anode being between 0.5 cm and 2 cm, and said potential means providing a potential difference between said photocathode and said anode of between 50 kV and 100 kV.