Liquid Crystal Variable Waveplates (Retarders) are constructed using precision polished, optically flat fused silica windows spaced a few microns apart. The cavity is filled with nematic liquid crystal material and sealed. This assembly ensures excellent transmitted wavefront quality and low beam deviation, required for many demanding applications. Uncompensated retarders can vary from 30nm - λ/2 retardance while compensated retarders can operate from 0 – λ/2.
The long axis of the liquid crystal molecules defines the extraordinary, or slow, index. With no voltage present, the molecules lie parallel to the windows and maximum retardance is obtained. When voltage is applied across the liquid crystal layer, the molecules tip towards the direction of the applied electric field. As voltage increases, the effective birefringence decreases, causing a reduction in retardance. The basic liquid crystal controller allows a single retarder to be controlled manually.