Alice uses an array of potassium bromide and caesium iodide type photocathodes. Different photocathodes provided differing spectral responses. Various filters, photocathodes, and electronics aided in collecting data in several ultraviolet light passbands. Caesium iodide photocathodes are highly efficient at extreme ultraviolet wavelengths. Solar blind photocathodes were not of direct military use and are not covered by "generations". The photocathodes can be made of a variety of materials, with different properties. Photocathodes divide into two broad groups; transmission and reflective. While the listed requirements can be applied generally, photoanodes and photocathodes have slightly different needs. Photocathodes operate in a vacuum, so their design parallels vacuum tube technology.