Cholesteric matrix, effect

Absorbing systems circular dichroism When linearly dichroic dye molecules are dissolved in a cholesteric liquid crystal the medium exhibits circular dichroism because of the helical arrangement of the solute molecules in the structure. The theory developed above can be extended to take into account the effect of absorption by treating the layers as both linearly birefringent and linearly dichroic. Assuming that the principal axes of linear birefringence and linear dichroism are the same, the Jones matrix of any layer with reference to its principal axes is... 

The limitations on multiplexing any rms-responding monostable liquid crystal effect have been mentioned in Section II.A. Active matrix addressing, described in Sectin IV.A, is one way of overcoming these limitations. Another is to consider alternative liquid crystal effects that are bistable, or at least non-rms responding. With such effects, the maximum number of rows that can be multiplexed is usually determined by the ratio of the frame time (the time period during which the whole picture must be refreshed or updated) to the line time (the time required to address one row of pixels). This is quite demanding of the line time a frame time of 40 msec (only 25-Hz frame rate) would require a line time of 40 /xsec for 1000 lines. Bistable behavior is associated with smectic and cholesteric phases, both of which in completely different ways have translational symmetries added to nematiclike orientational order. In this section, the ferroelectric tilted smectic devices are reviewed, while (untilted) smectic A and cholesteric devices are described in Section IV.C. 

Liquid crystal induced circular dichroism (LCICD) examines the differential absorption of circularly polarized radiation by an achiral solute oriented in a cholesteric liquid crystal. The circular dichroism results from an induced Cotton effect in the achiral solute due to the macroscopic chirality of its ordering in the helical solvent matrix. The effect has been shown theoretically to arise... 

Polymer dispersed liquid crystal (PDLC) devices usually contain N phases as the liquid crystal material [71] and are used in vision products [72], e.g., privacy windows, projection displays [73], and direct view displays [74, 75]. Cholesteric liquid crystals have also been used [76]. All these devices relax back to the original ground state when the field is removed. Ideally such films consist of dfoplets of liquid crystal in a polymer matrix the reverse situation (reverse phase) consists of a liquid crystal continuum with polymer balls dispersed within it. The latter films are not desirable, because they do not provide reversible electrooptic effects. 

The cholesteric-to-nematic phase transition effects have also been utilized in matrix-addressed displays. Up to 28 lines have been scanned in the V V/S mode with a bias voltage of 35 Vrms and a contrast ratio of 15 1. The relatively large multiplexing capability is due to the long decay time produced by the bias voltage. ... 

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