High-speed Imaging of Spatiotemporal Liquid Crystal Switching Dynamics

Liquid crystals (LCs) are widely used for light modulation in industrial and commercial applications including device display technologies and optical switches for telecommunications. The elongation of LC molecules and their alignment to applied electric fields confers their unique electro-optical properties. However, their temporal response or `switching speed' due to an applied electric field is the primary limitation governing the overall performance of LC devices. To engineer better LC materials and faster devices, detailed knowledge of complex electrodynamic phenomena in LCs is required, yet no diagnostic methods are currently available to characterize fast temporal dynamics with high spatial resolution. In an effort to mediate this gap between instrumentation and LC physics, we have developed a technique based on high-speed imaging and polarization microscopy, which is used to characterize the spatiotemporal dynamics of LC switching on millisecond time scales with micron spatial resolution. To demonstrate the efficacy of this high-speed imaging method, we characterize the switching time scale for a standard Freedericksz cell as a function of the applied voltage. As a second industrially-relevant LC device geometry, we microfabricated an in-plane switching device that generates a highly non-uniform electric field, enabling us to measure spatial variations in switching speed within a single micro-scale device. Experimental results were compared with theoretical models to benchmark results, and also to quantitatively determine the LC switching dynamics from processed digital high-speed videos.