How would you like to own a 335-page book on the physics and engineering of electron photoinjectors? For free!
That is what you will get if you click on the link. If you are ever interested in electron accelerators, especially at the "birthing" end where the electrons are generated and given the initial acceleration, this is the review book to get. It explores not only the engineering aspect of the photoinjectors, but also the physics of photocathodes, and what makes a good photocathode for accelerator applications.