Simultaneous measurement of retardance and fast axis azimuth based on liquid crystal wave plate group

Abstract

The simultaneous measurement of retardance and fast axis azimuth based on liquid crystal wave plate group (LCWPG) is presented. The laser beam propagates through an aperture and then splits into two beams by a non-polarizing beam splitter (NPBS). The intensity of the reflected beam is detected by a photomultiplier tube (PMT) as the reference light intensity. The transmitted beam, which passes through a polarizer, a quarter-wave plate, a retarder sample to be measured and the LCWPG successively, is finally detected by another PMT. The LCWPG is composed of four liquid crystal wave plates (LCWPs). In addition, the LCWPG works in six different polarized modulation modes dependent on the voltages applied on each LCWP. The six corresponding sets of light intensity are then measured by the two PMTs. By calculating and deriving from the six sets of light intensity, the retardance and fast axis azimuth of the measured sample can be obtained, respectively. In the experiment, the retardance of a quarter wave plate as the sample is measured when its fast axis is at different angles. The standard deviations of the retardance and the fast axis azimuth of the measured sample are 0.67˚ and 0.85˚, respectively. The effectiveness of the proposed method is verified.