John E. Bigelow

Contrast optimization in matrix-addressed liquid crystal displays

In a fast-scan mode of addressing a matrix of m rows and n columns, in which the columns are scanned, contrast is optimized by maximizing the ratio of the rms voltage at a selected intersection to that at a nonselected one. A simple derivation shows that the address-pulse amplitude should be taken proportional to n1/2. We apply this result to the twisted nematic case.

Transient observations of field‐induced nematic‐cholesteric relaxation

We have found that the relaxation process in the electric‐field‐induced cholesteric‐nematic transition depends upon sample boundary conditions. Homeotropic samples exhibit a delay time, followed by nucleation of the decay sequence about isolated surface defects. Transient capacitance measurements and cinemicrophotography of this process are reported for the first time.

Comments on the Relaxation Process in the Cholesteric-Nematic Transition

The relaxation process by which a field-aligned nematic state returns to a helicoidal structure has been the subject of several studies. In this paper, we report some new transient optical and capacitive measurements which emphasize the dependence of the relaxation on sample boundary conditions. Homeotropic samples exhibit a delay time after field removal, followed by nucleation of the decay sequence about isolated points. During the decay, the capacitance decreases monotonically, but the light-scattering transient is structured even in the absence of polarizing optics. A spiral domain structure is observed for these samples. For samples with parallel boundary conditions, the transient capacitance data exhibit a minimum which supports earlier inferences of a tilted-Grandjean-planar structure.