哈工大信息光学Chapter7-2.pdf

幻 灯 片 1 Chapter 7 Wavefront modulation Weimin Sun College of Science Harbin Engineering University 幻 灯 7.2.1 properties of liquid 片 crystals •Solid ?Anisotropic Liquid?Isotropic •As T increases, order parameter decreases. 2 Crystal: S=1; LC: S~0.6-0.8, Isotropic: S=0. n T Crystal Nematic LC Isotropic 幻 Smectic :近晶相 灯 Molecular arrangements for Nematic :向列相 片 different types of LCs Cholesteric: 胆甾相 3 SMECTIC A SMECTIC B SMECTIC C Order NEMATIC CHOLESTERIC 幻 Ferroelectric ：铁电的 灯 Bistable : 双稳态的 Unique Features of Each LC Phase 片 4 1. Nematic LCs: •Uniaxial; Simple alignment; Good gray scale; Low voltage; Millisecond response time •Mainstream liquid crystal display material 2. Ferroelectric (Smectic C) LCs: •Layered structure; Bistable; µs response time Limited gray scale; Thin (1 -µm) cell gap •Sensitive to DC voltages 3. Cholesteric LCs: pitch •Helical structure; Bragg reflection •Bistability fi Low power displays 幻 灯 Key Molecular Structures 片 5 TN TN-TFT R CN R