Rami Arieli: "The Laser Adventure"

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:

Active medium and its importance for the lasing process.
Population inversion in the active medium, and the conditions for making it (Excitation of the active medium with an external source of energy).
Stimulated emission and light amplification caused by it.
Laser system and its components (chapter 3).

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

First, a few concepts from wave theory are needed:

What are standing waves.
What are the conditions for creating standing waves.
How standing waves in a laser cavity are determined by the laser design.

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.