Rami Arieli: "The Laser Adventure" Chapter 8 Section 2, page 8
Littrow Prism
Actually, when wavelength selection of the laser output is needed, it is enough to use a prism which has the laser reflecting mirror on one of its surfaces.

Such mirror is called Littrow prism, and is described in figure 8.11.

Figure 8.11: Littrow prism as a single wavelength selector in a laser.

The angle of the prism in this case is half the Brewster angle.

In such prism laser beam is refracted only twice in a round trip, compared to 4 times in a regular mirror.

The limit of Littrow prism is that it enable half the tuning capability of regular prism.

The main use of Littrow prism is to limit lasing to a specific wavelength from a few available.