Liquid-crystal modulator

Fig. 33. Diffraction efficiency versus voltages for spatial frequencies in mm-1 10 (/), 28 (2), 51 (i). Switch on time versus voltages at spatial frequencies in mm"110 (/ ), 36 (2 ), 60 (S ). Commutational regime for polyimide-liquid crystal modulator with controlled birefringence [256]...

The pulse shaper is a device made of a pair of gratings and lenses, arranged in a zero dispersion compressor, and a liquid crystal modulator placed in the Fourier plane. Liquid crystal arrays allow one to influence independently spectral phase and amplitude with discretization of 128 pixels each. 

The major problem with extending these shaping methods into the mid-IR is the availability of a suitable modulator. There are many different types of phase and amplitude modulators that work in or near the visible, including liquid crystal modulators (LCM), Te02 and fused silica acoustooptic modulators... 

S. T. Wu, A. M. Lackner, and U. Efron, Optimal operation temperatirre of liquid crystal modulators,... 

S. T. Wu, A nematic liquid crystal modulator with response time less than 100 ps at room temperature, Appi Phys. Lett. 57, 986 (1990). 

FIGURE 5.26. Comparison of the liquid crystal modulation curves obtained by different procedures (a) treating the substrate with lecithin and (b) spontaneous homeotropic orientation, (x) indicates experimental data, the solid lines represent the calculated values [157, 163]. Anchoring energy in calculations was changed to fit the experimental data, d = 5 /z, Ae = 0.02. 

Liquid crystal modulators, placed on the plane, where the Fourier image of the object is formed (Fig. 8.10), are widely used as one of the important parts of optical correlators [60] used, in particular, in real-time object tracking systems [61]. Liquid crystal modulators could be made as a-Si H-FLC light valves [62] or TV modules [61, 63], working in a special video feedback regime. 

From this analysis it is possible to see why FLC SLMs form a vital part in optical systems. The liquid crystal modulation allows the display of information into coherent optical systems as both intensity and phase images. The nature of the FLC molecular interaction makes it fast and this ideally suits nondisplay applications. Even the restriction of binary modulation does not limit the usefulnes of FLC SLMs, although fast grey scale and multilevel phase modulation would be desirable. In fact, for some applications, binary modulation is a bonus and enhances performance. 

The physical construction of a Fabry Perot filter is shown in Fig. 54. The liquid crystal modulation needs to be parallel to the direction of the light in order for a refractive index change to be achieved. For this reason, the liquid crystal molecules must be tilted off the surface of the mirrors to allow the modulation to occur. The electrical field which moves the molecules must be applied from the side of the cell rather than the front... 

A Shearographic Inspection System Using a Liquid Crystal Phase Modulator. 

Wefers M M and Nelson K A 1995 Analysis of programmable ultrashort waveform generation using liquid-crystal spatial light modulators J. Opt. Soc. Am. B 12 1343-62... 

An LCD is a ubiquitous electronic display. Now, it is widely distributed among human daily life, like mobile phones, TV, and personal computers. The LCD has, however, a drawback, i.e., slower response than a plasma display or an electroluminescene display. Recently we have first succeeded in combination of a nanoparticle technology with the LCD technology, which realized fast response of the LCD [45,235,236]. Thus we have found a phenomenon, i.e., a frequency modulation of the LCD doped with metallic nanoparticles. Since the frequency modulation, or electro-optic property depends on the kind of metals, we have prepared AgPd bimetallic nanoparticles protected with a typical liquid crystal molecule, 4-cyano-4 -pentylbiphenyl (5CB) to investigate the electro-optic property [45,235,236]. 

Cholesterol s presence in liposome membranes has the effect of decreasing or even abolishing (at high cholesterol concentrations) the phase transition from the gel state to the fluid or liquid crystal state that occurs with increasing temperature. It also can modulate the permeability and fluidity of the associated membrane—increasing both parameters at temperatures below the phase transition point and decreasing both above the phase transition temperature. Most liposomal recipes include cholesterol as an integral component in membrane construction. 

In video microscopy, for instance, background is normally subtracted using differential interference contrast (DIC) [18]. This technique, which requires a number of manipulations from the user, may now be automated using a new method called polarization-modulated (PMDIC) [19,20], It requires the introduction of a liquid crystal electro-optic modulator and of a software module to handle difference images. PMDIC has been shown to bring improvements in imaging moving cells, which show a low contrast, as well as thick tissue samples. 

A very different model of tubules with tilt variations was developed by Selinger et al.132,186 Instead of thermal fluctuations, these authors consider the possibility of systematic modulations in the molecular tilt direction. The concept of systematic modulations in tubules is motivated by modulated structures in chiral liquid crystals. Bulk chiral liquid crystals form cholesteric phases, with a helical twist in the molecular director, and thin films of chiral smectic-C liquid crystals form striped phases, with periodic arrays of defect lines.176 To determine whether tubules can form analogous structures, these authors generalize the free-energy of Eq. (5) to consider the expression... 

Electrooptic displays, liquid crystal polymers in, 75 110 Electrooptic effect, 74 675 Electrooptic modulation, second-order nonlinear optical materials for, 77 444... 

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