Gary A. Dir

Optical storage effects in liquid crystals

Abstract The electro-optic behavior of two chemically identical liquid crystal mixtures was compared. It was determined that ethoxybenzylidene- p ′- n -butylaniline (Eobuta) doped with 10% 1-methanol exhibited pronounced optical storage, whereas Eobuta doped with 10% racemic menthol only exhibited dynamic scattering. Since Eobuta doped with 1-menthol is cholesteric and Eobuta doped with racemic menthol is nematic, it was concluded that optical storage capability is an intrinsic property of the cholesteric state, and in agreement with the observable textures, should be viewed as a reversible plane ⇄ focal-canic texture change.

Simple real‐time light valves

A simple real‐time light valve based on selenium and the cholesteric‐nematic phase transition is described. The device is optically addressed and can be read out in real time with very intense white light sources without need for an optical blocking layer. Operation involves the absorption characteristics of the photoconductor and space‐charge‐limited currents. The principle can be extended to other combinations of photoconductors and electro‐optic effects.

Ultralow‐voltage image intensifiers

A novel reflective image intensifier based on the twisted nematic electro‐optic effect is described. The device can be read out with intense actinic radiation without need for an optical blocking layer. Images of very high resolution and excellent tonal range can be obtained at voltage levels as low as 1.6 Vrms.

Dynamics of Texture Transitions in Cholesteric-Nematic Mixtures

Abstract Several time-dependent electro-optical properties of a cholesteric-nematic mixture have been investigated. In particular, the dynamics of the Grandjean ⇆⇆ focal conic texture transitions have been characterized. A cholesteric-nematic mixture was used comprising molecules having a net tendency to align with their long axes perpendicular to the applied field, allowing the study of the field induced focal conic →→ Grandjean transition. D.C. electro-hydrodynamic effects were employed in the investigation of the Grandjean →→ focal conic transition. The driven and relaxation properties of the electro-hydrodynamic induced transition are described. Also, the memory properties of intermediate textures of this transition are discussed. Thickness is found to play a crucial role in the relaxation of the textures. The time to achieve the electro-hydrodynamic induced texture transition (Grandjean →→ focal conic) is found to be controlled in a non-linear fashion by applied voltage and only weakly by current. Fo...

Light sensitivity enhancement of image intensifiers

It was observed that liquid‐crystal–photoconductor reflective light intensifiers, without optical blocking layers, become more sensitive to the imaging light when the irradiance of the actinic read‐out light is increased. Measurements illustrating the effect and an interpretation are presented.

INDUCED ROTARY POWER IN TERNARY MIXTURES OF LIQUID CRYSTALS

We have observed that a ternary mixture comprising one nematic component and a compensated binary cholesteric results in an inversion wavelength (λo) in the near infrared for a broad range of nematic ratios. In particular, the system consisting of N — (p — methoxybenzylidene) — p — butylaniline, cholesteryl nonanoate and cholesteryl chloride was studied over a wide compositional region. Measured pitch values indicate a large deviation from the linear additive law. An interpretation lies in the possibility that both cholesteric species interact with the nematic, but with different strengths. Consequently, the nematic exhibits some net rotary power. A determination of coupling constants will be presented.

Conductivity Differences in the Cholesteric Textures

Both the focal conic and Grandjean textures can be characterized by a conductivity tensor with uniaxial symmetry. We have observed that the diagonal element corresponding to the conductivity in the special direction is ≈ 20% larger in the focal conic case. The film studied was a mixture of 80% N-(p-methoxybenzyli-dene)-p-butylaniline and 20% cholesteryl oleyl carbonate. The transformation to the focal conic texture was produced by the application of a dc voltage and the reverse transformation was induced by an ac voltage. At sufficiently low current levels, current does not perturb structure (at least to the extent that the optical and electrical properties are not altered). At higher levels, the measuring stimulus converts the film to an intermediate state and both textures approach the same current level since they are converted from their original symmetries into the same state. The conductivity differences observed are consistent with conductivity ratio data for the nematic component and the molecular distributions in the two textures. The influence of resistivity and temperature on the focal conic/Grandjean conductivity ratio is shown.

LED printbar image plane characterization

Light emitting diode (LED) printbars are finding wider use as imaging devices in digital copiers and printers. The key to their acceptance in high quality printers requires tight control of the image plane irradiance profile. As a first step in understanding the imaging capabilities of an LED printbar a measurement system was developed to characterize the radiometric performance of the printhead from a slit scan of the image plane. From this scan of the image profile, statistics on the pixel to pixel irradiance, pixel to pixel placement, and pixel to pixel image size and shape are developed for an entire LED printhead.