Physics of photopolymer-liquid crystal composite holographic gratings

We present an overview of the physics of holographic grating formation and electro-optical switching in a unique polymer-dispersed liquid crystal material. Anisotropic counter-diffusion of liquid crystal (LC) molecules and monomers during holographic recording appears to produce conditions favorable for distorting phase-separated sub-micrometer LC droplets into prolate ellipsoids with major axes along the grating vector. A simple shaped-droplet mechanical model yields results in good agreement with optical diffraction data for polarization properties and switching fields as well as response and relaxation times, as long as droplets can be assumed to be positive uniaxial domains. Normal surface anchoring of LC molecules is likely in these systems, based on NMR data, and this tends to strongly influence the effective refractive index and birefringence of the droplets.