Optical response time

When the backflow and inertial effects are ignored, the dynamics of the LC director reorientation is described by the following Erickson-Leslie equation [9,10]  

Under such circumstances, both rise time and decay time have simple analytical solutions [43]  

both rise time and decay time are defined while transmittance (under crossed polarizers) changes from 10% to 90%. In the above equations, is the LC director reorientation time (1 1/e) and Sg is the net phase change from a bias voltage U= V), to V=0  

Equation (8.33) correlates the optical rise time and decay time to the LC director reorientation time (To). Basically, it is a linear relationship except for the additional logarithm term of the phase dependence. 

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Fig. 17 Temperature dependence of electro-optical response time for the polymer-stabilized blue phases (polymer fraction a = 6.3, 10.5, 15.0 mol %) in the rise process (A) and decay process (B) [46]...

Figure 4 Optical response time for PG253, as a function of temperature, to an applied sinusoidal ac field of 207V rms, 4kHz. Sample thickness = 45+2]im. 

Electro-optic response times were measured by heating the material from ambient to the required temperature, applying a pulsed ac field and measuring the response time for the light... 

Figure 5 Optical response times for PG253 as a function of applied voltage (f = 2.5kHz sinewave). T = 129.7 C and thickness =...

Figure 8 Optical response time for PG296 as a function of temperature. V rms = 300 sinewave at f = 2kHz. Thickness = 45 + 2ym.

An electro-optic storage effect has been demonstrated in smecto-genic side chain polymer liquid crystals. The storage effect is observed above Tg and would appear to be a result of the high viscosity and bistable nature of these systems. The optical response times at temperatures of X SO C above ambient may be of the order of seconds or less. A number of factors that influence the response time have been identified ... 

The dielectric constants of the real (s ) and imaginary (e) parts for P2 were evaluated as a function of frequency. The response time of P2 in the SmC phase at 160 °C was estimated to be 1 s by using the s maximum at 1.1 Hz and the e" inflection at 1.5 Hz. The optical response time of P2 was 1 s with the application of DC 2 kV cm to the polymer-sandwiched ITO glass cell at 150 °C. This value is consistent with that obtained through measurements of the dielectric constants [59-64, 66]. The response time of 1 s for P2 is much smaller than those for ordinary LC conjugated polymers in nematic or smectic phases under an electric field (about 20-30 min for complete alignment). 

Although the dyes are used in relatively low concentrations, their effect on the material parameters of the host liquid crystal should not be overlooked. It has been suggested that some anthraquinone dyes can have a disproportionate slowing down effect on the electro-optic response time because of dye-induced changes in the viscosity coefficients. 

E. Jakeman and E. P. Raynes, Electro-optic response times of liquid crystals, Phys. Lett. A39, 69 (1972). H. Imura and K. Okano, Temperature dependence of the viscosity coefficients of liquid crystals, Jpn. J. Appl Phys. 11, 1440 (1972). 

From Equation (8.6), the LC director s relaxation time is governed by the cell gap (d) and the LC visco-elastic coefficient (Y1/K22), and is independent of the rubbing angle. In a VA cell, the optical response time is about 50% of the LC director s response time. 

H. Wang, T. X. Wu, X. Zhu, and S. T. Wu, Correlations between liquid crystal director reorientation and optical response time of a homeotropic cell, J. AppL Phys. 95, 5502 (2004). 

Fig. 21. Electro-optic response times for a twisted nematic device as a function of polymer concentration. The polymer was a polysiloxane backbone system (as in Figs 19 and 20) dissolved in a nematic cyanobiphenyl compound. Ihe applied voltage was 5Vn, , the cell thickness was 12jum and data are...

Figure 7. Electro-optical response times vs. the magnitude of applied electric field.

The observed optical response time is related to ultrasonic relaxation rates. It is noted that the optical response time can be identified with the order parameter, allowing simple interpretation of the result. 

Another noninvasive tool to measure temperature is the infrared (IR) thermometer, which usually has an optical response time below 0.1 s. The measurement principle is based on determination of the thermal radiation Q oi a target body. The radiation is proportional to the temperature of the body according to the Stefan-Boltzmann law... 

Fast electro-optical response time of the order of few femtoseconds [2] ... 

E. Jakeman and E. P. Raynes, Electro-Optic Response Times in Liquid Crystals, Phys. Lett., 39A, p. 69(1972). 

Jakeman, E. and Raynes, E. P., Electro-optic response time in liquid crystals, Phys. Lett. A,... 

Fig. 1.30 Temperature T dependence of the electro-optical response time -r of three low-molar-mass L (FLC) and their corresponding polymers P (FLC). The notations of the chiral groups are 1 MB for 1 -methylbutyloxy carbonyl EL for...

Figure 1.30 shows temperature T dependence of electro-optical response time t (the time in which a 10-90 % change takes place for the electro-optical response when a square wave electric field = 10 MV/m is applied) for three different low-molar-mass FLCs that consist of three different chiral end groups respectively, and their corresponding FLCPs that consist of a common polyoxyethylene main chain. 

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