Rami Arieli: "The Laser Adventure" Chapter 8 Section 0, page 1
Chapter 8:
Controlling the laser radiation properties
Laser radiation properties can be divided into two groups:
  1. Spatial properties - which describe the intensity and phase distribution in space at specific moment.
  2. Wavelength spectrum emitted from the laser.
Accordingly, controlling the laser radiation properties is divided in two subjects:
8.1 Controlling the Spatial beam properties:
8.1.1 Controlling the Transverse optical modes of the beam (within the optical cavity).
8.1.2 Controlling the beam after it is emitted out of the optical cavity.
8.2 Controlling the wavelength spectrum emitted from the laser:
8.2.1 Controlling the wavelength spectrum emitted from the laser by a prism inside the optical cavity.
8.2.2 Controlling the wavelength spectrum emitted from the laser by a grating at the end of the optical cavity.
8.2.3 Choosing specific longitudinal optical mode by etalon.