Nonlinear optics of liquid crystalline materials

MULTIPLE TIME SCALES OPTICAL NONLINEARITIES OF LIQUID CRYSTALS FOR OPTICAL-TERAHERTZ-MICROWAVE APPLICATIONS (Invited Review)

“…Nematic liquid crystals are uni-axial, characterized by refractive indices n and the n ⊥ , for light polarization parallel and orthogonal to the director axis, respectively. The magnitude of nematic birefringence Δn = n − n ⊥ is among the largest of all known materials, on the order of 0.2 that holds from the visible through far infrared and well into the microwave regime [1][2][3][41][42][43][44][45][46][47][48], c.f. Figure 3 and Table 1.…”

“…In particular, we will investigate all the major mechanisms leading to the so-called optical Kerr effect [49] where the laser induced refractive index change is of the form: Δn = n 2 I [I is the optical intensity and n 2 is the nonlinear index coefficient]. As detailed in the following sections, nonlinear index coefficients characterizing these nonlinear optical processes are among the largest of all known materials, ranging from ∼10 −11 cm 2 /Watt for ultrafast individual molecular electronic nonlinearities to well over 10 3 cm 2 /W for liquid crystalline ordered phase nonlinearities [2][3][4][5]. In contrast to [36].…”

“…Here (α l , K l ) and (α t , K t are the values of the components of molecular polarizability and local field correction tensor K parallel and perpendicular to the principal axis, respectively; N A is the Avogadro number, M the molecular weight, and ρ the density [1][2][3]. S is the magnitude of the order parameter tensor…”

“…In the next few sections, we shall discuss the fundamentals of these mechanisms and their dynamical characteristics, and explore the possibilities of utilizing them for fast responding all-optical switching and modulation operations. For completeness and possibly new applications, we also include a brief discussion of the ultrafast (femtoseconds) molecular electronic nonlinearities [49,[77][78][79][80][81][82][83][84][85] of NLC, as well as the isotropic (liquid) phase nanoseconds orientation nonlinearities [3,52,53].…”

“…The applied fields could create one or more of the splay-, twist-and bend-types of lattice distortions, as well as fluidic flows with velocity v, as shown in Figure 6. Field induced director axis reorientation is described by the continuum theory [1][2][3] which begins with the Free energies associated with the resulting distortions: …”