Photokathoden

Photokathoden is a type of photosensitive material that was commonly used in electronic imaging devices, particularly in cameras and television systems. The term "photokathoden" is German for "photo cathode," which refers to the fact that it releases electrons when exposed to light.

This material consists of a layer of alkali metal, typically cesium or potassium, that is applied to a glass or metal surface. When light falls on the photokathoden, it excites the electrons in the metal atoms, causing them to be emitted from the surface. The emitted electrons can then be collected and used to generate an electrical signal.

Photokathoden was widely used in imaging devices from the 1920s to the 1960s, particularly in television systems where it was used to convert the image from a camera tube into an electrical signal. The photokathoden is particularly sensitive to ultraviolet and visible light, making it suitable for use in devices where the image is formed by light. However, it has some limitations, such as being sensitive to temperature and humidity changes, which can affect its performance.

The use of photokathoden has largely been replaced by other types of photosensitive materials, such as photocells and image intensifiers, which offer better performance and durability. Nevertheless, it remains an important part of the history of electronic imaging and understanding its principles is still relevant today.