We investigate the fabrication of holographic polymer dispersed liquid crystals (H-PDLCs) for use as switchable laser cavities. H-PDLCs are liquid crystal and polymer dispersions used in grating applications for displays, optical communications and optical security. By controlling the pitch of the H-PDLC and the laser dye used, we are able to fabricate a tunable laser. H-PDLCs were made in both reflection and transmission modes to vary the method by which lasing action occurs. The dye-doped H-PDLCs were pumped with nanosecond pulses from a laser with emission at 532 nm and a power of approximately 6 mJ. Lasing action was observed using a spectrometer from the H-PDLC grating; peak wavelengths occurred over a range of wavelengths, depending on the dye used, with the full width of the emission peaks approximately 6-8 nm at half maximum. The lasing action can be turned on and off by the application and removal
of an electric field due to the properties of an H-PDLC. Furthermore, we investigate multidimensional architectures and quasicrystal symmetries for lasing applications. Applications for these cells include use in small-scale portable devices requiring a tunable laser source.
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 switchability of the lattices and tunability 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.