A scalable vacuum photosensor configured to simplify mass production with a housing having an evacuated first side at an ultrahigh vacuum and a second side which does not require high vacuum. The first side of the device is sealed to a base plate, having a central electron readout element, using an oxide-free sealing technique, with the deposited sealing areas serving as high voltage throughputs from the first to second sides. A conductive photocathode layer on the transparent first side converts photons to photoelectrons and concentrates the photoelectrons upon the readout. The first and second sides together form an electrostatic lens for accelerating and focusing photoelectrons upon the readout, preferably having a scintillator which generates secondary light measured by an optical detector in the second side of the housing.