Spectroscopy of laser active media

Familiarity with the energy level structure in the active medium of a laser can help in understanding why particular pumping mechanisms are employed and how population inversion is achieved. Also, the allowed modes of operation (CW, pulsed, Q-switched, etc.) of a laser system are dictated by the excitation and decay kinetics of the excited states. Optical spectroscopic studies of the active media can provide insight into the operation of the different types of lasers and at the same time illustrate spectroscopic techniques as well as aspects of the energy level structure of solid, liquid, and gaseous media. A range of experiments and exercises are described illustrating concepts which are common to courses, both in optical spectroscopy and in the physics of lasers, and which could form a useful experimental option to such courses.