BIREFRINGENCE MEASUREMENTS OF LIQUID-CRYSTALS AND AN APPLICATION - ANACHROMATIC WAVEPLATE

We demonstrate a quarter wave phase retarder consisting of two layers of different liquid crystals (LCs). The phase retardation does not dif fer by more than +/-5% from the target value pi/2 within a spectral in terval of 200 nm in the visible range. These values are comparable to the data for commercial two layer crystalline retarders which are much more expensive, especially if large apertures are required. In order to design the LC retarder we measured the birefringence of the LC with in the entire visible spectrum using a published technique which does not consider interference effects due to reflections within indium-tin oxide coated LC cells. We show that these effects do not affect the r esults adversely provided that the birefringence data are taken over a broad spectral range.