Rami Arieli: "The Laser Adventure" Chapter 4 Section 0, page 1
Chapter 4:
Optical Cavity and laser Modes

Before explaining the details of each of the laser components, few terms must be understood:

Chapter 4 explains the conditions which determine the radiation modes created in common lasers.

First, a few concepts from wave theory are needed:

Second, the properties of the optical signal which is amplified while passing back and force through the active medium are discussed.

Third, longitudinal modes are created in the laser cavity. Their importance and methods for controlling them are discussed.

Forth, the distribution of energy along the cross section of the beam, which determine the transverse modes, is explained.
At the end of chapter 4 the common optical cavities are described and the way to test their stability.