Rami Arieli: "The Laser Adventure"

Rami Arieli: "The Laser Adventure" Chapter 8 Section 2, page 13

Etalon

Etalon is an additional short optical cavity inserted into the laser optical cavity.

Etalon is composed of two mutually parallel surfaces.

The distance between the two surfaces is about the size of the gain curve of the laser. Thus, only one longitudinal mode is under the gain curve each time, as seen in figure 8.13.

Figure 8.13: Choosing single Longitudinal Mode with an Etalon.

There are two optical cavities inside the laser with etalon.

Longitudinal mode can exist in the double cavity structure only if it simultaneously fulfill the conditions of standing wave for both cavity lengths.

The linewidth of the etalon longitudinal mode is determined by the reflection of its surfaces. The higher the reflection, the narrower the longitudinal mode of the etalon.