Basic Theoretical Considerations of Light Amplification by Stimulated Emission of Radiation

摘要

A theoretical development of the basic physical principles of Light Amplification by Stimulated Emission of Radiation (LASER) is presented. The processes of absorption and emission are presented in a general manner, using both a classical and quantum mechanical approach. The classical approach involves the approximation of the motion of an atomic electron as a driven oscillator. The quantum mechanical approach employs the time-dependent perturbation approximation to develop the transition rates for absorption and emission. A brief discussion of the lifetime and spectral line width of excited energy states is presented due to their importance in considerations of the LASER. Following this general development of the absorption and emission processes, a qualitative discussion of the important aspects of the LASER mechanism is presented. A quantitative development of the conditions for amplification for the two basic types of LASER (the three-level and four-level types) is presented using ruby and neodymium-doped glass as typical examples. (Author)