Introduction of Liquid Crystal device into THz phase imaging

摘要

We investigate the terahertz (THz) phase imaging using liquid crystal (LC) device. Recently, there have been extensive efforts to measure the refractive indices and transmission losses of some LC materials in THz region. From these results, LC materials show relatively large refractive index anisotropy and they can have a potential application to some control devices similar to the display application. Furthermore, tunable LC THz phase shifter has been reported. In this study, an attempt was made to introduce the LC device into the THz phase imaging which was based on four-step phase-shifting algorithm. Four-step phase-shifting algorithm is one of the most effective methods of phase imaging and moving mirror is needed to introduce phase shift in standard measurements. In addition, we should prepare the two rays with common source, therefor experimental setup becomes complicated. While on the other hand, it is just needed to insert a LC phase shifter into the light path when we adopt LC device. Furthermore, low-voltage application is enough to introduce the phase-shifting, hence it is not necessary to prepare the moving mirror. In this work, we fabricate the electrically tunable LC phase shifter which has sandwich cell structure. The fundamental phase-shifting properties were measured by using an optically pumped gas laser system which can generate continuous wave (CW) THz waves. In addition, we investigated the phase shifting interferometry which was based on four-step phase-shifting algorithm by using LC phase shifter. We also estimate the birefringence of X-cut crystalline quartz at 2.5 THz.