Lecture
This lecture covers the concepts of Einstein coefficients, population inversion, and light amplification. It explains the relationship between stimulated and spontaneous emission, the detailed balance at equilibrium, and the steady-state solutions of a two-level system. The lecture also delves into the transient problems of turning on and off a light source, the 3-level system, and the history of laser development. Additionally, it discusses the use of different laser media, such as gas lasers, solid-state gain materials, and dye lasers. The presentation concludes with the practical aspects of laser technology and the first commercial lasers in the 1960s.