Thresholdless

Exploitation of these is possible in LEDs that display coherence properties, in thresholdless laser diodes, and in many other optical, opto-electronic and quantum electronic devices. 

The second application uses the converse flexoelectric effect, i.e. a field-induced splay-bend distortion, to generate a fast, symmetric and thresholdless linear electro-optic effect in a cholesteric liquid crystal. 

Fig. 7.5. Increasing curvature in response to an increasing electric field the thresholdless field-induced periodic splay-bend deformation. The pattern in the director field is shown to the left (in any oblique cut perpendicular to the optic axis) and the optic axis deflection with increasing field is shown to the right. (From Rudquist et reproduced with kind permission of Taylor Francis, http //www.tandfonline.com.)...

P. Rudquist, S.T. Lagerwall, N.A. Clark, J.E. Maclennan and D.M. Walba, Symmetric thresholdless electrooptic effects in liquid crystals. In Proc. 20th IDRC, SID OO, Palm Beach, 24-28 September 2000, pp. 59-63. 

The last criterion (4) is bistability. In the non-helical structure the direction of the polar axis is fixed in the sense that the three vectors, the polar axis Pj, the director n and the smectic normal h form either right or left vector triple. This depends on molecular handedness and cannot be changed. In this sense there is no bistability. On the other hand, the Goldstone mode allows the thresholdless rotation of Pj together with n about h through any angle by an infinitesimally low electric field. So, a number of possible states is infinite. 

Normally, as the g-value does not exceed 0.01, CPL photoresolution rarely leads to the ee value over 0.5%. The ee value cannot be easily determined by the common methods. However, because the conversion from the nematic to the cholesteric is essentially thresholdless, theoretically the ee value is high enough to induce a nematic to cholesteric phase transition and can be determined from the cholesteric pitch via Equation 5.1. Similarly, the helicity of a cholesteric phase for this system can be controlled by only using the chiral information in the CPL. At last, the transition from the cholesteric to the nematic phase can be caused by irradiation with UPL or linearly polarized light (LPL) with the racemization of chiral switches or motors. 

The molecular interaction between each lajrer is weak and the molecular directors in one layer are not strongly bound by molecular directors in the adjacent layers. As a result, neither a ferroelectric liquid crystal state nor an antiferroelectric liquid crystal state can be realized in forming this random orientation. In the early stages, these materials were called thresholdless antiferroelectric liquid crystals (TLAF) . However, for these materials antiferroelectric order or antiferroelectricity cannot be observed. Recently, the terms frustoelectricity and frustrated electricity have been proposed [36]. These terms imply that the formation of both ferroelectricity and antiferroelectricity are prohibited and neither phase can be formed. 

Figure 9.28 illustrates the electro-optic responses observed at two 0 s 0° and 30°, where 0 is the angle between the layer normal and one of the crossed polarizer directions. As shown in Figure 9.28 [92], the electric field dependence of transmittance at 0 = 0° shows the typical thresholdless, hysteresis free, V-shaped switching. From the electro-optic measurements at every 5° of 0, the transmittance T versus 0 was obtained at given electric fields. Figure 9.29(a) shows three examples of T versus 0 curves at applied fields of 0, +6, and 6 V/pm [92]. The transmittance T is described by... 

Inui, S. N. limuro, T. Suzuki, H. Iwane, K. Miyachi, Y. Takanishi, and A. Fukuda. 1996. Thresholdless antifeiroelectricity in liquid crystals and its application to displays. J. 

---