Nonlinear phenomena generation

Second-harmonic generation of light is a nonlinear phenomenon in which chaotic behavior was discovered in 1983 [83] (for details, see Secction ). In the Kerr effect with an external time-dependent pump, a chaotic output may also occur, which was proved for the first time in 1990 by Milbum [84] (see also Section III). 

Materials are also classified according to a particular phenomenon being considered. AppHcations exploiting off-resonance optical nonlinearities include electrooptic modulation, frequency generation, optical parametric oscillation, and optical self-focusing. AppHcations exploiting resonant optical nonlinearities include sensor protection and optical limiting, optical memory appHcations, etc. Because different appHcations have different transparency requirements, distinction between resonant and off-resonance phenomena are thus appHcation specific and somewhat arbitrary. 

An analysis of the recent observation data [30,31] shows that baroclinic Rossby waves that are generated off the eastern coasts in the northern parts of the Pacific and Atlantic oceans in a period of about a year represent their dominant non-stationary dynamical response to the annual cycle of the atmospheric forcing in the latitudinal range from 10-15° to 45-50°N. In so doing, their mean phase velocities (0.02-0.03 ms 1 at 40-45°N) are higher than the theoretical values (about 0.01 ms-1). A similar situation is observed in the Black Sea as well [27]. In [32], several reasons of this phenomenon were listed such as the interaction with more large-scale non-stationary processes, topographic and nonlinear effects, and insufficient duration and spatiotemporal resolution of the observation data. 

Extended nonequilibrium thermodynamics is concerned with the nonlinear region and deriving the evolution equations with the dissipative flows as independent variables, besides the usual conserved variables. Typical nonequilib-rium variables such as flows and gradients of intensive properties may contribute to the rate of entropy generation. When the relaxation time of these variables differs from the observation time they act as constant parameters. The phenomenon becomes complex when the observation time and the relaxation time are of the same order, and the description of system requires additional variables. 

Together with PAP, photo-induced depoling (PID) is another interesting phenomenon at the interface of photochemistry and organic nonlinear optics. Indeed, PID of poled polymers occurs when NLO chromophores, which are oriented in a polar manner, undergo photoisomerization without applied dc field. The chromophores lose their initial polar orientation after photoisomerization and reorientation in azimuthal directions around the initial polar axis, thereby erasing FID has been observed both by photo-induced destruction of EO Pockels and by second harmonic generation. The first published PID experiments have been reported for DRl in PMMA, and the theory of PID is discussed in detail in reference 25. 

In general, a vast number of optical transduction techniques can be used for biosensor development. These may employ linear optical phenomenon (e.g. adsorption, fluorescence, phosphorescence, and polarization) or nonlinear phenomena (e.g. second harmonic generation). The choice of a particular optical method depends on the analyte and the sensitivity needed. Total internal reflection fluorescence (TIRF) has been used with planar and fibre-optic wave-guides as signal transducers in a number of biosensors. 

Most of the studies devoted to the nonlinear optical properties of metal nanoparticles use the notation x (<>>) to refer to the susceptibility for the optical Kerr effect. Unless otherwise specified, we will also adopt this simplified designation in the following. Let us just recall that it corresponds, in fact, to an experimental situation where a unique plane wave, linearly polarized (or three plane waves with same polarization and frequency), generates the third-order nonlinear optical phenomenon in an isotropic medium at the same frequency, and that the susceptibility is a priori a complex quantity. 

The phase distribution function (143) allows for calculations of the phase variances for the individual modes as well as the phase correlations between the two modes by performing simple integrations over the phase variables Qa and 0/,. Detailed discussion of the phase properties of the fields can be found in Ref. 16, and we will not repeat it here. The material presented in this section has been chosen as to illustrate how quantum noise, which is an indispensable ingredient of quantum description of optical fields, can be incorporated into the theory of nonlinear optical phenomena, in particular the phenomenon of second-harmonic generation. 

Nonlinear optical properties have recently been observed for the polysilane (PhMeSi) 132, suggesting that polysilanes may eventually find use in optical technology. Irradiation of a thin film of the polysilane at 1064 nm gave rise to efficient third-harmonic generation, while irradiation at 1907 cm-1 produced no nonlinear signal. The third-harmonic resonance is believed to be due to a three-photon process, but its origin is uncertain. Farther research will undoubtedly be carried out on this new phenomenon. 

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