Mesoscale lattices and temporal multiplexing in liquid crystallpolymer dispersions

We demonstrate multi-beam holographic lithography and temporal multiplexing techniques to create complex two- and three-dimensional structures in holographic polymer-dispersed liquid crystal (H-PDLC) materials. H-PDLCs are a variant of PDLCs formed under holographic conditions. The holographic image is typically a two-beam interference pattern, resulting in an array of liquid crystal (LC) droplets and solid polymer planes that act as a Bragg grating. Applying an external electric field can reversibly erase the resulting refractive index modulation. Using multi-beam holographic lithography, two-dimensional square lattices and three-dimensional FCC lattices have been created. The structures of the created lattices have been confirmed using a scanning electron microscope. We demonstrate the switchabilty of the lattices and tunablity of the photonic bandgaps upon application of an electric field. Instead of simultaneously exposing a sample to multiple laser beams, we have developed a technique for creating complex structures by time-sequentially exposing the sample with multiple holographic configurations. By time- sequentially exposing the sample, two switchable reflection gratings are formed in a single film. The reflectance of the resulting gratings is well controlled by the individual exposure time. The optical performance can be modeled using a 2x2 matrix method based on the reaction diffusion equation.