Palto S P, Barnik M I, Geivandov A R, Kasyanova I V, Palto V S
Shubnikov Institute of Crystallography, RAS, Leninsky prospekt 59, 119333 Moscow, Russia.
Phys Rev E Stat Nonlin Soft Matter Phys. 2015 Sep;92(3):032502. doi: 10.1103/PhysRevE.92.032502. Epub 2015 Sep 14.
Transmission of planar layers of cholesteric liquid crystals is studied in pulsed electric fields perpendicular to the helix axis at normal incidence of both linearly polarized and unpolarized light. Spectral and light polarization properties of the primary photonic band and the field-induced bands up to fourth order of Bragg selective reflection are studied in detail. In our experiments we have achieved an electric field strength several times higher than the theoretical values corresponding to the critical field of full helix unwinding. However, the experiments show that despite the high strength of the electric field applied the helix does not unwind, but strongly deforms, keeping its initial spatial period. Strong helix deformation results in distinct spectral band splitting, as well as very high field-induced selective reflectance that can be applied in lasers and other optoelectronic devices. Peculiarities of inducing and splitting the bands are discussed in terms of the scattering coefficient approach. All observed effects are confirmed by numerical simulations. The simulations also show that liquid crystal surface anchoring is not the factor that prevents the helix unwinding. Thus, the currently acknowledged concept of continuous helix unwinding in the electric field should be reconsidered.
研究了在垂直于螺旋轴的脉冲电场中，线性偏振光和非偏振光垂直入射时胆甾相液晶平面层的透射情况。详细研究了主光子带以及高达布拉格选择性反射四阶的场致带的光谱和光偏振特性。在我们的实验中，我们实现了电场强度比对应于完全螺旋展开临界场的理论值高出几倍。然而，实验表明，尽管施加的电场强度很高，但螺旋并未展开，而是强烈变形，保持其初始空间周期。强烈的螺旋变形导致明显的光谱带分裂，以及可应用于激光器和其他光电器件的非常高的场致选择性反射率。根据散射系数方法讨论了带的诱导和分裂特性。所有观察到的效应均通过数值模拟得到证实。模拟还表明，液晶表面锚定不是阻止螺旋展开的因素。因此，目前公认的电场中连续螺旋展开的概念应重新考虑。
