Nonlinear phenomena second-harmonic 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). 

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. 

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. 

The interfaces in general, and particularly with solid substrates break the head-to-tail symmetry of a liquid crystal phase and induce polar orientational order. The symmetry is reduced to the conical group Coov The latter allows a finite value of the second-order nonlinear susceptibility X2 responsible for the second optical harmonic generation [11]. This phenomenon has been observed in experiments on generation of the second harmonic in a ultrathin nematic layers on a solid substrate as shown in Fig. 10.9. 

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