Basic photoelectric conversion device based on external photoelectric effect.
The electric tube can convert light signals into electric signals. There are two types of vacuum photocells and gas-filled photocells. The typical structure of the photoelectric tube is to evacuate the spherical glass shell, coat a layer of photoelectric material on the inner hemisphere as the cathode, and place a small spherical or small ring metal as the anode in the center of the sphere. If the ball is filled with low-pressure inert gas, it becomes a gas-filled photocell. The photoelectron collides with gas molecules in the process of flying to the anode to ionize the gas, which can increase the sensitivity of the photocell. Metals used as photocathodes include alkali metals, mercury, gold, silver, etc., which are suitable for the needs of different wavebands.
The photoelectric tube has low sensitivity, large size, and easy damage, and has been replaced by solid photoelectric devices.