Tuning Wedge Etalon is composed of a wedge of transparent material with special coatings, as seen in figure 8.15.

By changing the position of such Etalon in a perpendicular direction to the optical axis, a different width is seen by the laser radiation, Thus a different longitudinal mode will be emitted out of the laser.

Such Etalon enable continuous tuning, because for each width against the optical cavity, a different condition for standing wave must be fulfilled.