Dc-Pockels effect

P(-gd Pockels effect dc-P Electro-optical Pockels Effect (EOPE)... 

Table 5.25 NR contribution to the dc-Pockels effect (P" (-oo m,0)(o- oo) of LiOCeo in the infinite optical frequency approximation...

In addition to the static vibrational properties, the NR contributions to the dc-Pockels effect of Li C6o in the infinite optical frequency approximation were also reported in Ref [61] (Table 5.25). Compared with their electronic counterparts the values were small, but not negligible. 

The argument Rp implies structure relaxation in the field, and P" means the nuclear relaxation part of P, while the subscript oc oo invokes the so-called infinite optical frequency (lOF) approximation. In principle, this procedure allows one to obtain most of the major dynamic vibrational NR contributions in addition to the purely static ones of Eqs.4.5. 7. The linear term in the electric field expansion of Eq. (4) gives the dc-Pockels effect the quadratic term gives the optical Kerr Effect and the linear term in the expansion of beta yields dc-second harmonic generation (all in the lOF approximation). For laser frequencies in the optical region it has been demonstrated that the latter approximation is normally quite accurate [29-31]. In fact, this approximation is equivalent to neglecting terms of the order with respect to unity (coy is a vibrational frequency). In terms of Bishop and Kirt-man perturbation theory [32-34] all vibrational contributions through first-order in mechanical and/or electrical anharmonicity, and some of second-order, are included in the NR treatment [35]. 

The remaining (higher-order) vibrational contributions can, in principle be computed as well using a related formulation [36]. However, that treatment requires computation of the field-dependent zero-point vibrationally averaged properties, which was not feasible for the systems studied here because of their large size and complicated potential energy surface (PES). Indeed, of the dynamic properties mentioned above, we were only able to obtain the dc-Pockels Effect due to instabilities for high fields that wiU be described later. 

At time t = 0, a dc field is applied it produces an electric field-induced Pockels effect (EFIPE), which is solely due to a third-order effect Eq) in the case of the copolymer because the molecules are not oriented by the dc field alone at room temperature, but which also contains a part due to the rotation, in a polar manner, of free chromophores in the guest-host system (induced The value of x is measured from the modulations of ATR... 

In the same way as in the two previous sections, the first hyperpolarizabilities associated to three different nonlinear effects were calculated the static response and two dynamic effects, the dc-Pockels response characterized by P(-(b o),0) and the second harmonic generation response, p(-2 to, ). Again, in the dynamic case ffl=1.16 eV. The results are listed in Tables XIV, XV, and XVI for the ID clusters, and in Tables XVII, XVIII, and XIX for the 2D and 3D clusters. Similarly to the dipole moment case, only the major tensor component, Paaa> is considered. 

P( P(-o> w,0) P(0 -fa>,w) Y( - Y(-2(i) (i>,tD,0) Y(-o) (i>,0,0) Second harmonic generation (SHG) Electrooptic Pockels effect Optical rectification Third harmonic generation DC electric-field-induced SHG Intensity-dependent refractive index Optical Kerr effect Coherent anti-Stokes Raman pSHG pEOPE pOR. yTHG. EFISH oj DC-SHG. JlDRI or. yOKE. yCARS... 

Combination with Static Fieids. A common technique, useful for optoelectronic devices, is to combine a monochromatic optical field with a DC or quasistatic field. This combination can lead to refractive index and absorption changes (linear or quadratic electrooptic effects and electroabsorption), or to electric-field induced second-harmonic generation (EFISH or DC-SHG, 2 > = > - - third-order process. In EFISH, the DC field orients the molecular dipole moments to enable or enhance the second-harmonic response of the material to the applied laser frequency. The combination of a DC field component with a single optical field is referred to as the linear electrooptic (Pockels) effect co = co + 0), or the quadratic electrooptic (Kerr) effect ( > = > - - 0 -I- 0). These electrooptic effects are discussed extensively in the article Electrooptical Applications (qv). EFISH is... 

Each expansion contains only a single second-order dispersion coefficient A- Since these coefficients for different optical processes of a given order are equivalent (Bishop 1995), they express the dispersion of frequency-dependent properties in a way that is transferable between different optical processes, for instance A describes both the second-harmonic generation and the (dc-)electro-optic Pockels effect. 

Noncentrosymmetric crystals show other properties in addition to frequency conversion, for instance the linear electro-optic or Pockels effect the linear change of the refractive index induced by an applied DC electric field. Furthermore, the point groups and allow for the existence of a permanent electric dipole moment. Indeed, crystals... 

In a motor-driven self-nuUing ellipsometer, the dc feedback currents are used to drive servomotors instead of being passed through the Faraday cell. As an alternative to the polarizer modulation described above, crystals with electro-optic effect (e.g., Pockels effect) can be used to modulate the relative phase retardation by an electric ac field. Independent modulations of polarizer... 

Linear electro-optic effect (Pockels effect) refers to the modification of the refractive indices of certain NLO materials by a low-frequency or (DC) electric field. The amplitude of modulation field is assumed to be much larger than the light field Ex Ej. The resulting small refractive index change is linearly proportional to the electric field ... 

Because of the extensive overlap with electro-optics and nonlinear optics, the reader is referred to separate articles on these topics in this encyclopedia. See ElectroopticAL Applications for a discussion of the changes in the optical response of polymers dne to an applied AC or DC electric field from the so-called Pockels or Kerr effects. Also see, for an overview. Nonlinear Optical Properties. 

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