phase shifting optics
To be able to increase the resolution of a fizeau interferometer
phase shifting is a common way. There are several ways to achive
phase shifting. One is to incorporate 1/4 wave plates and linear
polarisators, another way is to fine tune a laser. The most simple
way is however to physically change the distanse between the
referense mirror and the measuring surface.
A piezoelectric crystal is a good element to fine tune the mirror. A
electric charge on a piezo crystall will change the thickness.
A typical crystal 1mm thick can change the thickness a
couple of um wich is enough to fine tune the mirror at atomic
levels.
A simple way to test this is to take a crystal from a speaker element. 0.5mm thick appr 24mm in diameter.
The first setup to test the phase tuning of a fizeau
interferometer. A piezo element is placed between two flat glass
plates. Two thin glasspieces are placed on the oppsite side of the
glass to get two parallel surface wich laser light interfere (650nm).
This crude simple test showed a change of 4 fringes when a voltage of
30V were applied. This corresponds to a physical change of the crystal
of appr 2um. (In the speaker this is used in AC mode to create sonic
waves but works fine in DC mode also)
