Two crystal plates variable phase retarder system

The system of two crystal plates with the particular orientation of optical axis and location plates relatively to each other can be used as adjustable retarder with specific properties. The phase difference between ordinary and extraordinary beams depends on plates thickness an angle between plates and incidence angle of light on two plates system. Under certain conditions system is characterized by a special direction – pseudo optical axis. This direction can be detected experimentally by observing the interference picture – conoscopic figure of optical system.