We report the optical characterization of a dual-frequency hybrid aligned nematic ͑HAN͒ liquid crystal cell driven between two states using a multiple-frequency sinusoidal pulse. The complex dynamic director structure formed during the fast switching process is resolved in unprecedented detail on a submillisecond time scale. The results reveal backflow effects and a total switching time that is substantially faster than that achievable with conventional HAN cells. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1992672͔To allow liquid crystal devices to maintain their position as the primary flat-panel display, the quality of video rate images, dominated by the switching speed of the pixels, must be improved. This fundamental limitation is dictated by the viscoelastic properties of the liquid crystal, and to overcome this problem both the structure of the liquid crystal cell and the material itself must be considered.One potential fast-switching structure is the hybrid aligned nematic ͑HAN͒ cell, which has already been demonstrated as a commercially significant geometry in the new generation of zenithal bistable devices. 1 A HAN cell has homogeneous alignment on one surface and homeotropic alignment on the other. To a first approximation, this geometry offers equal bias to both homogeneous and homeotropic alignment, resulting in a near-linear variation in tilt with distance through the cell. On application of a voltage across a HAN cell, a thresholdless distortion can readily be produced, aligning the director either homeotropically or homogeneously depending on the sign of the dielectric anisotropy of the nematic liquid crystal used. 2,3 An interesting possibility arises when a HAN structure is combined with a dualfrequency liquid crystal; 4,5 these materials have a high dielectric dispersion where the dielectric anisotropy, ⌬ ͑f͒ = ʈ ͑f͒ − Ќ ͑f͒, is frequency dependent, resulting in a change in sign at the crossover frequency f co , where ⌬ ͑f co ͒ = 0. Certain dual-frequency materials are commercially available in which f co occurs at a few kHz and ⌬ ͑f͒ changes significantly over the range 1 -100 kHz. In a dual-frequency HAN cell, the director can be driven between either homogeneous or homeotropic alignment with equal ease by applying an electric field across the sample at a frequency either above or below f co . 6 This provides a relatively straightforward means of switching the cell between the birefringent homogeneous alignment and the uniaxial homeotropic alignment, which are both optically very different from the relaxed 0 V state.Optical waveguide techniques have become one of the leading tools for the detailed measurement of the director profiles in numerous liquid crystal structures. 7-9 A modification to the synchronization of voltage application and data collection in the standard fully leaky guided mode ͑FLGM͒ technique 10 has now been implemented, allowing the director orientation during dynamic reorientation to be recorded on an unprecedented 2 s time scale. This time-resolved FLGM techni...