Electro-optic Cell Research Articles

Transients in an electrooptic cell with delayed negative feedback

The dynamic properties of an electrooptic cell used in lasers with external feedback are analyzed. A cell in a negative feedback loop allows an equidistant spectrum of harmonics in the feedback signal which is applied to the electrodes.This spectrum is bounded by virtue of the frequency properties of the negative-feedback circuit. The characteristics of the transients in a cell of this sort have been determined for the first time: the conditions for self-excitation, the decay time, and the period of the oscillatory process. The conditions for stability in the negative-feedback circuit have been studied. The stabilizing properties of this cell are estimated.

Orientation of large DNA during free solution electrophoresis studied by linear dichroism

DNA T7 (40 kbp), T5 (120 kbp) and T2 (170 kbp) have been studied under electrophoretic conditions in free solution (25 mmol dm–3 ionic strength) regarding chain orientation and field-free decay using phase-modulation detected linear dichroism. The steady-state orientation does not show Kerr-law behaviour for the larger T5 and T2 DNAs but increases roughly linearly with field strength, the orientation factor being around 3 × 10–3 at 100 V cm–1. When subjected to the electric field DNA displays within 0.1–5 s an orientation overshoot which increases strongly with DNA size and comes faster the higher the field strength. When the field is switched off a major portion of the DNA orientation has relaxed within 10 ms while a smaller portion decays more slowly: 0.3 s for T2, comparable with the slowest relaxation of a Zimm–Rouse chain. The observed orientation phenomena could be important in free-solution capillary electrophoresis of DNA. The question of the mechanism by which the DNA is aligned (dipole or electrophoretic orientation?) cannot be addressed adequately within existing theories for chain-like macromolecules. Awaiting results from simulations it is speculated that the overshoot phenomenon and the slow decay component of large DNA may represent reptative deformations of the DNA coil similar to those recently observed for large DNA during gel electrophoresis. Rapid field reversal did not lead to any dip in steady-state orientation for the pure DNA; however, in a complex with the recombinase protein RecA which stacks outside DNA, apparently in a polar way to form a large permanent dipole, a pronounced dip suggests that there is a 180° rotation of the particle upon field reversal. The electro-optical cell was designed to give minimal influence from electro-osmosis and convection. The experiments on T2 and T7 DNA (on the ground) were replicated under microgravity conditions during a sounding-rocket flight without any noticeable differences in orientation dynamics.

Local layer structure of the steep field line defect in surface-stabilized ferroelectric liquid crystal cells

Abstract The local layer structure of one type of DC electric field induced line defect observed in CS-1014 surface stabilized ferroelectric liquid crystal electro-optic cells has been determined using X-ray scattering and optical microscopy. The characterized defect is a high contrast defect line distinct from other field lines in that a defect mirror image is not produced when the DC field direction is reversed.

Properties of Electro-Optic Cells with Chiral Dichroic Two-Frequency Liquid Crystals and Their Use for Thermal Mapping

Experimental results obtained with the two-frequency driven guest-host electrooptic cells are described. Applicability of these cells as planary temperature indicators with critical temperature smoothly adjustable during measurements is discussed

Two-Frequency Driven Liquid Crystal Electrooptic Cell with Nematic-Cholesteric Phase Change

Abstract Electrooptic properties were measured of the two-frequency driven guest-host type electro-optic cells with nematic-cholesteric phase change. The realization of temperature indicators with tunable critical temperature is proposed on the basis of electrooptic cells or PDLC films filled with dichroic (chiral) nematic mixtures which show low frequency dielectric relaxation phenomena.

A demonstration of loss modulation and cavity dumping in a free-electron-laser oscillator

The performance of an intraactivity cadmium telluride electro-optic cell in a free-electron laser will be described. The cell, installed in the Stanford Mark III IRFEL, was used to either modulate the optical-cavity losses or to dump the stored optical-cavity energy or both. The results of the experiments will be presented.

Ferroelectric Liquid Crystal Electrooptic Cell with High Contrast Bistability

Abstract Electrooptic cell with surface stabilized ferroelectric liquid crystal having high contrast bistability was realized using a conventional rubbing method. Permanent quasi-bookshelf structure with stripped texture was induced by applying a low frequency electric field in the cell.

Ferroelectric liquid crystals with large spontaneous polarization and high speed display devices

Abstract Ferroelectric liquid crystals with large spontaneous polarization exceeding 10-7 C/cm2 prepared by taking the following design factors into consideration are discussed; (a) separation between the chiral carbon and the dipole moment, (b) bulky molecular group connected to the chiral carbon, (c) introduction of large bond moments, (d) orientation of many bond moments around chiral carbon, (e) dipole moment between the core and chiral carbon, (f) the dipole moment at the core, and (g) the effect of hydrogen bonds. Anomalous dielectric behavior in these new ferroelectric liquid crystals and high speed response times of less than several tens of μs in electro-optic cells have also been discussed.

Electrooptical investigations on a nematic two frequency addressing mixture

AbstractThe change of the sign of the dielectric anisotropy of a nematic liquid crystal allows an active switching process in electrooptical cells in on and off direction. In the two frequency addressing mode the TN cell shows a qualitative and quantitative different dynamic behaviour in comparison to the conventional driving mode. During the switching on process hydrodynamical domains occur. After switching off the director configuration skips into the −3π/2 twist and thereby it realizes a loss in transmission. The director configuration relaxes into the quarter twist after some minutes. A superposition of low frequent and high frequent voltage gives a strong increase of the number of multiplexable lines.

A simple electro-optical Kerr cell for conducting liquids with low Kerr constant

A simple electro-optical Kerr cell for conducting liquids with low Kerr constant

Depolarization of monochromatic radiation in an electrooptic switch

It is shown that an electrooptic Pockels cell can be used to obtain radiation with zero time-average polarization. Possible ways of operating such a depolarizer are considered. The results are given of an experiment involving depolarization of laser radiation by an ML-5 electrooptic switch.

A fast electro-optic focusing device

A dynamic focus method is described which enables the instantaneous focus to be changed dynamically to give an optimum focus for the object illuminated by the laser beam. The dynamic focus method employed uses a three-stage electro-optic focusing device. Each stage of the device consists of an electro-optic cell and a birefringent lens. Performance results are presented for a two state focusing device which demonstrates the feasibility of the system. The switching rate is 158 kHz and the rise-time of the cell is 40 ns.

Multicolor fluorescent display by scattering states in liquid crystals

Cholesteric and nematic liquid-crystal electro-optic cells are described which function as both UV shutters and as tunable fluorescent emitters ( shutter cells ). Two-color displays of blue-green, blue-red, or green-red are achieved in the double-layered structure of the shutter cell with an external passive fluorescent element. Contrast ratios of about 5 in these two-color pairs are achievable by electrically switching the shutter cell. Display characteristics for several fluorescent guest materials are measured and their dependence on various system parameters is discussed. Multicolor fluorescent displays are made by using a triple-layered structure of shutter cells and passive elements.

Multicolor fluorescent liquid-crystal display concepts

A cholesteric liquid-crystal electro-optic cell is described which functions as both a UV shutter and as a tunable fluorescent emitter (’’shutter cell’’). By interfacing such a cell with an external passive fluorescent element, a two-color display can be achieved. Contrast ratios of about 5 in the two-color pairs blue-green, blue-red, and green-red are achievable by electrically switching the shutter cell. Multicolor displays can be made by stacking shutter cells and passive elements.

ChemInform Abstract: ELECTROCHROMISM IN ANODIC IRIDIUM OXIDE FILMS. II. PH EFFECTS ON CORROSION STABILITY AND THE MECHANISM OF COLORATION AND BLEACHING

AbstractDas elektrochrome Verhalten von anodischen Ir‐oxid‐Filmen (elektrochemisch auf eine Ir‐Reflektorelektrode aufgebracht) wird in Lösungen verschiedener Acidität untersucht.

Electrochromism in Anodic Iridium Oxide Films: II . pH Effects on Corrosion Stability and the Mechanism of Coloration and Bleaching

The oxidation state of iridium ions in an oxide film, grown electrochemically on an Ir metal reflector electrode, can be rapidly and reversibly modulated according to the electrochromic redox reactionBy suitable choice of electrolyte composition and potential limits, the coloration and bleaching processes can be effected without causing oxide film growth or dissolution, or electrolyte decomposition. Color‐bleach (c‐b) cycles exhibit reflectance contrast changes, , and charging times, τ, suitable for electrooptic display devices, e.g., for a film 320 nm thick, at and . Long term corrosion stability is obtainable in mildly acidic sulfate electrolytes, e.g., at pH 3.5. Sulfate electrolytes are also apparently unique in preventing degradation of c‐b response times owing to changes in film structure. East write‐erase times are made possible by the highly porous and hydrated nature of the oxide film and the ready availability of the protons required for bleaching from an ‘internal’ source—free molecules in the electrolyte contained within the film pores and/or bound or OH groups on the oxide surface. The kinetics and mechanism of the electrochromic reaction in anodic iridium oxide films are discussed with particular reference to the requirement for preserving electroneutrality within the bulk oxide. Recent claims that this redox reaction can occur without exchange of protons with the electrolyte are shown not to be substantiated. Attractive features of the electrochromic iridium oxide system for display devices include: (i) broad spectral absorption; (ii) good contrast ratio; (iii) fast response; (iv) good corrosion stability; (v) good open‐circuit memory in the presence of water and dissolved ; (vi) suitable threshold and switching voltage levels; and (vii) the ability to grow and reform the oxide layer in situ in the electrooptic display cell. The charge (∼20 mC cm−2) and energy (∼30 mJ cm−2) required for coloration and bleaching are similar to those required for other electrochromic oxide systems, e.g., the tungsten bronzes.

The Guest-Host Interaction in Liquid Crystals: 2. A New Fast Fluorescent Shutter

Abstract A new fast optical shutter, based on the guest-host interaction using a fluorescent dye, has been demonstrated. Using acridine orange as guest in a cyanobiphenyl nematic host it has been shown that the shutter can be turned on or off in a few milliseconds. The electro-optic cell, which has a 2mm optical path length, uses transverse electric fields and both field strength and frequency dependence studies have been made. It has been shown that both increases and decreases in transient light levels may be obtained by changing the polarisation state of the incident or emergent light.

The Guest-Host Interaction in Liquid Crystals: 1. A New Fast Dichroic Shutter

Abstract A new fast optical shutter, based on the guest-host interaction, that uses a 2 mm optical path length, has been demonstrated. Using a suitable pleo-chroic dye as guest in a cyanobiphenyl nematic host it has been shown that the shutter can be turned on and off in a few milliseconds. The electro-optic cell uses transverse electric fields, and field strength, frequency and temperature studies have been made. It has been shown that both increases and decreases in transient light levels may be obtained by changing the polarisation state of the incident light.

Undamped resonance spiking by internal modulation of pulsed solid state lasers

Cavity loss modulation is investigated in the low-frequency range of pulsed Nd-lasers. The response of the system shows a typical resonant behaviour, whose resonance frequency is equal to the frequency of the relaxation oscillations. The resonance step-up is in the order of 10 3, which means that an extremely small driving voltage at the electrooptic cell results in very regular, undamped spikes. Experiments are performed with a pulsed Nd: YAG laser. Pulse power, half-width, and distance are in the range required for controlled material removal in high quality laser material processing.

New multicolor liquid crystal displays that use a twisted nematic electro-optical cell

Two new variable color display device arrangements are described. These arrangements combine the unique polarization switching capabilities of the twisted nematic liquid crystal electro-optical cell with the anisotropic optical properties of separate passive optical elements. In one scheme, the passive element is a birefringent film in combination with a neutral polarizer, and colors are transmitted by the selective interference of white light. In another design, where the passive element is a pleochroic filter, the transmitted colors result from the selective absorption of white light. These arrangements make possible large area displays, since the colors transmitted do not depend on the temperature or thickness of the nematic layer. Transmission curves and other color information are given for a number of examples.