Giant optical nonlinearity

S. G. Odulov, Yu. A. Reznikov et al., Photostimulated Cange of Phase-Transition Temperature and Giant Optical Nonlinearity of Liquid Ci ystals, Sov. Phys. JEPT (1983) 224... 

A giant optical nonlinearity of self-focusing type in the oriented mesophase of nematic liquid crystals (NLC) due to the director reorientation under the action of a light wave field is predicted. Self-focusing of He-Ne laser radiation with power lO" W and power density - 50 W/cm in a planar oriented 60 jum thick NLC layer has been carried out experimentally. The measured value of the nonlinearity effective constant 2 0.07 cm /erg corresponds to theoretical predictions, and turns out to be larger than the CS2 nonlinearity by sl0 times. 

The reorienution of the director of a nematic liquid crystal induced by the field of a light wave is considered. An oblique (with respect to the director) extraordinary wave of low intensity yields the predicted and previously observed giant optical nonlinearity in a nematic liquid crystal. For normal incidence of the light wave on the cuvette with a homeotropic orientation of the nematic liquid crystal, the reorientation appears only at light intensities above a certain threshold, and the process itself is similar to the Fredericks transition. The spatial distribution of the director direction is calculated for intensities above and below threshold. Hysteresis of the Fredericks transition in a light field, which has no analog in the case of static fields, is predicted. 

Photostimulated change of phase transition temperature and giant optical nonlinearity of liquid crystals... 

Optical field-induced director reorientation is responsible for the largest nonlinear optical susceptibility observed in liquid crystals, the largest in any known material. Although the process is slow, the nonlinearity is about 10 times greater than that of CS2. Because of its magnitude, the orientational nonlinearity of liquid crystals has been termed giant optical nonlinearity (GON). 

An interesting and important point is that, at low optical power, the orientational effect actually is the dominating one, even in such highly absorptive material. In other recent studies " of dye-doped nematic liquid crystals, observed nonlinearities have approached the so-called supranonlinear scale characterized by refractive index coefficients n2 1 cm /W. The observed nonlinearity is orders of magnitude larger than the so-called giant optical nonlinearity of pure liquid crystals. In particular, methyl-red dye-doped nematic liquid crystals were first observed to have a nonlinear index... 

H. Schmidt, and A. Imamoglu. Giant Kerr nonlinearities obtained by electromagnetically induced transparency. Optics Letters 1996 Dec 1 21(23) 1936-1938. 

In [133], devoted to the orientational optical nonlinearity of liquid crystals, some additional effects observed in cholesterics are considered the giant optical bistabilty, grating orientational nonlinearity, pitch change due to the direct action of light and to the thermal effects, hysteresis, and optical bistability and nonlinearities connected with absorption. Here we cite some... 

Shalaev, V.M. (2001). Fractal nano-composites giant local-field enhancement of optical responses, In Nanoscale linear and nonlinear optics, Bertolotti, M. and Sibilia, C. (Ed.) AIP. 

Collective optical excitations, like surface plasmon-polaritons in partially-ordered metal nanoparticle arrays, tend to be spatially localized. The localization facilitates a giant increase of linear and nonlinear optical responses such as Raman scattering, enhancement of spontaneous emission rate, nonlinear absorption and refraction. In this paper the spectral manifestation of light localization into metal-dielectric nanocomposites i s s tudied i n t he visible. T he e ffect o f t he 1 ateral e lectrodynamic coupling on transmission/reflection optical spectra is investigated for planar silver nanoparticle arrays (random close-packed and polycrystalline quasiregular structures). Combined action of electron and photon confinements is demonstrated experimentally and considered theoretically for ID-photonic crystals consisted of a metal nanoparticle stratified array. 

Composite materials formed by nanometer-sized metal particles embedded in dielectrics have a growing interest o wing to the large values of fast optical Ken-susceptibility, whose real part is related to the intensity-dependent refractive index 2 [ ] Ion implantation has been shown to produce a high density of metal nanoparticles (MN) in glasses [2], The high-precipitate volume fraction and small size of MN leads to giant value of the [3]. This stimulates an interest in the use of ion implantation to fabricate nonlinear optical materials. 

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