Study of dynamic gratings in methyl-red doped nematic liquid crystal E7 using polarized pump-probe technique

Abstract

The large optical nonlinearity of nematic liquid crystals makes them promising materials for various applications such as dynamic holography, image processing and adaptive optics. The optical nonlinearity in nematic liquid crystals is six orders of magnitude larger than conventional nonlinear materials and is appropriately referred to as a giant optical nonlinearity (GON). When the liquid crystal is made sensitive to visible light by adding small amounts of dye (typically less than 1%), the nonlinearity is further enhanced by as much as two orders of magnitude. Sensitivity to light intensity as low as 40 μW/cm² have been observed in methyl-red doped liquid crystals. Different contributing mechanisms have been proposed to explain the nonlinearity in dyed-nematics − conformational changes, intermolecular torque, space-charge fields and thermal effects. These mechanisms can have different characteristic times and the resulting response time of the nonlinearity is likewise affected. Discriminating between these effects is nontrivial due to the coupling that occurs.
In this research, we utilize the optical nonlinearity of methyl red-doped nematic liquid crystal to record dynamic gratings and use polarized pump-probe technique to study the nature of the optical nonlinearity.