Electro-optical effect high-frequency

The dielectric tensor describes the linear response of a material to an electric field. In many experiments, and particularly in optical rheometry, anisotropy in is the object of measurement. This anisotropy is manifested as birefringence and dichroism, two quantities that will be discussed in detail in Chapter 2. The nonlinear terms are responsible for such effects as second harmonic generation, electro-optic activity, and frequency tripling. These phenomena occur when certain criteria are met in the material properties, and at high values of field strength. 

Our first attempt to apply electro-optics in the investigation of the adsorption of neutral polyacrylamide on kaolinite particles was in 1988 [4,5]. Several electro-optical parameters were used to follow the adsorption of polymer on colloid particles—the amplitude of the electro-optical effect, the critical frequency of relaxation of the low- and high-frequency effects, the electro-optical decay time after the switching off of the electric field. Variations in these parameters with concentration of the added polymer give information on the particle electric polarizability, the thickness of the adsorbed polymer layer, the size of aggregates that appear in the suspension due to flocculation [4-10], etc. 

B. High-Frequency Dispersion of the Electro-Optical Effect... 

Figure 3 presents the frequency dependence of the electro-optical effects for suspensions of different volume fractions of spherical particles. The stock solution (8% sphere volume fraction) is highly deionized, and dilution is carried out with deionized water. Thus the highly dilute samples are in the liquid-phase state. Modulated responses are detected at low frequencies —- for highly dilute samples... 

Figure 9. Electro-optical effects of PMPPS, 50CB, PMPPS/50CB(50/50 molX) composite under low and high frequencies of an a.c. electric field. The applied voltage is 200 Vp.p and the cell thickness is 16 ym.

Spreiter, R., Ch. Bosshard, F. Pan, and P. Gunter. 1997. High-frequency response and acoustic phonon contribution of the linear electro-optic effect in DAST. Opt. Lett. 22 564-566. 

Crystals with one of the ten polar point-group symmetries (Ci, C2, Cs, C2V, C4, C4V, C3, C3v, C(, Cgv) are called polar crystals. They display spontaneous polarization and form a family of ferroelectric materials. The main properties of ferroelectric materials include relatively high dielectric permittivity, ferroelectric-paraelectric phase transition that occurs at a certain temperature called the Curie temperature, piezoelectric effect, pyroelectric effect, nonlinear optic property - the ability to multiply frequencies, ferroelectric hysteresis loop, and electrostrictive, electro-optic and other properties [16, 388],... 

The Pockel s effect [3] refers to an electro-optical process wherein the application of large electric fields onto crystals lacking a center of symmetry can lead to nonlinear polarization effects and optical rotation. Pockel cells can be used in place of photoelastic modulators and can achieve very high modulation frequencies but often have the undesirable property of a nonzero birefringence in the absence of an applied field. 

---