This article covers the fundamentals of lasers. Beginning with the nature of laser light itself, the mechanism of the laser is examined including basic rate equations. Gain and loss in a laser are analyzed and the laser cavity itself is modeled as an interferometer. Techniques of nonlinear harmonic generation as well as fast‐pulse production (
Q
‐switching) are examined. Finally an overview of the most common commercial lasers, including gas, solid‐state, and semiconductor types is provided. For each type of laser, output characteristics are examined as well as the specific mechanism of each.