Final answer:
A photo-cathode in image intensifiers acts to convert light into an electrical signal through the photoelectric effect, which is then amplified and used to construct images.
Step-by-step explanation:
The purpose of a photo-cathode in image intensifiers is to convert the light output from a scintillator into an electrical signal, using the photoelectric effect. When light strikes the photo-cathode, it emits electrons due to the photoelectric effect. These electrons are then accelerated and multiplied by successive dynodes with increasingly positive potentials, resulting in a strong output current that is proportional to the original light intensity, which can then be used to construct an image.
Devices like photomultiplier tubes utilize this process to amplify the light signals received from the scintillator, which is then processed by computers to create sophisticated and detailed visual images. This is critical in applications such as medical imaging, where high sensitivity and the ability to detect low-light scenarios are essential.