Photorefractive effects can be utilized in many areas, such as data storage, optical phase conjugation, real-time image processing and optical computing. Nematic liquid crystals(NLCs) possess many advantages over other photorefractive materials; low operating voltage and small intensity for writing.
In an attempt to facilitate the molecular orientation of nematic liquid crystals, MMONS(3-methyl-4methoxy-4'-nitrostilbene) was employed. MMONS has a large dipole moment and therefore it is expected that the MMONS molecules can assist to align the liquid crystal molecules along the space charge field so that the photorefractive effect may enhance.
Gain coefficient and diffraction efficiency were measured as a function of doping concentration of MMONS using the 1st-order Raman-Nath diffraction and two-beam coupling methods. Operation voltage was 4.5 V when the liquid crystal sample contained no MMONS. However operation voltage decreased to 1.4 V when the MMONS concentration was 1 wt%, which is about one third of that for the sample without MMONS.
By careful analysis of the data, we can draw a conclusion that MMONS molecules make a significant contribution to aligning the liquid crystal molecules at low voltages and hence to reducing the operation voltage.