Photoelectric Effect: Principles and Applications

This lecture discusses the principles of photoemissive detectors, focusing on the photoelectric effect. It begins by explaining the structure of metals, semiconductors, and insulators, highlighting the roles of inert and active bands. The instructor describes how electrons can be extracted from these materials when exposed to light, emphasizing the importance of photon energy in overcoming the work function. The lecture details the behavior of metals and semiconductors under blue and red light, illustrating how photon energy affects electron emission. The concept of effective affinity is introduced, explaining how surface treatments can alter electron behavior and create depletion regions. The instructor also covers negative affinity materials, where the vacuum level is below the conduction band, allowing for easier electron generation. Finally, the lecture explores the applications of photocathodes in both transmission and reflection modes, demonstrating their effectiveness in various wavelengths, particularly in ultraviolet light.