This document allows the students to use a simple approach in order to study the time evolution of the power output of a laser and its dependence upon the amplification coefficient, the length of the active medium, and the reflectivity of the cavity mirrors (Fig. 1). The document starts with a problem on finding the laser power at a given moment of time for the different values of the mirror reflectivity. After solving this problem, the students are guided to predict the optimal value of the mirror reflectivity using simple calculus, to check their prediction using Mathcad, and to present a physical explanation of their findings. Then they proceed to use Mathcad to analyze the dependence of the output intensity on the amplification coefficient, the length of the cavity, and time passed since the laser has been switched on. Afterwards, students design a hypothetical laser and present their design strategies and the results in their report. Finally, we discuss the limitations of the simple model used, and outline the more rigorous approach to study the dynamics of laser generation. The material in this exercise can be used within a first course in Physical Chemistry where lasers and their applications in chemistry are introduced. Instructor notes for this document give the rational for the model used and suggestions for completing some exercises.

Figure 1. Output laser signal as a function of the fraction of light intensity that passes through one of the laser mirrors.