Rami Arieli: "The Laser Adventure" Section 6.4 page 9
Tuning a Dye laser:
Choosing the right wavelength from a Dye laser is done by a prism or grating at the end of the optical cavity (see chapter 7). An example of tuning with a prism is described in figure 6.36a.
Figure 6.36a:Tuning a Dye Laser with a Prism.

An example of tuning with a grating is described in figure 6.36b.

Figure 6.36b:Tuning a Dye Laser with a Grating.