Electric degenerate four-wave mixing

Table 1 Coefficients for 7[ (a ) for third harmonic generation (THG), degenerate four wave mixing (DFWM), electric field induced second harmonic generation (ESHG), and Kerr effect in methane at the experimental geometry rcH = 2.052 a.u. A CCSD wavefunction and the t-aug-cc-pVDZ basis were used. (Results given in atomic units, the number in parentheses indicate powers of ten.)...

Absorption spectroscopy, quartz crystal microbalance and electrical measurements and femtosecond degenerate four-wave mixing studies of third-order optical non-linearity... 

Third-Order NLO Techniques. There is a wider range of third-order techniques commonly used to characterize materials, including electric field induced second harmonic generation (EFISH) (15, 16), third harmonic generation (THG) (17) and degenerate four wave mixing (DFWM) (18). EFISH and DFWM will be discussed briefly then... 

Poly(3-alkyl-a-thiophene) systems show significant third-order nonlinear susceptibilities ( ) Though, oligothiophenes have been studied for their third-order susceptibilities, accurate third-order optical nonlinearity data obtained by degenerate four-wave mixing or electric-field-induced second harmonic generation (EFISH) are difficult to attain reliably on samples with poor solubility characteristics (92MM1901). 

Under the influence of an optical pump, the molecular angular distribution described by Equation 12.4 can be considerably modified. In turn, this results in modification of the X/ kl tensor components. Further, we discuss the influence of a polarized pump beam on third-order nonlinear phenomena such as third harmonic generation (TFIG) [(described by XyfCL (-3a ,o ,w, u) coefficient], electric field induced second harmonic generation (EFISH) i 2co, (o, (o, 0)] and degenerate four-wave mixing (DFWM) X/yx/ -... 

Perpete, Quinet and Champagne have shown that vibrational contributions to the y-hyperpolarizability of various symbioticaUy substituted quadrupolar JT-conjugated molecules are large. Using ab initio calculations at the HF level they calculate the response functions for the dc-Kerr effect, degenerate four wave mixing, hyper-Raman effect and electric field induced SHG. 

FuIIerenes. - Perpete, Champagne and Kirtman have computed the vibrational contributions to the main non-linear optical response functions for the fiillerene Ceo- They use normal co-ordinates obtained in a DFT approximation combined with Hartree-Fock ab initio calculations of the electrical properties. Vibrational contributions to the electro-optic Kerr effect and degenerate four wave mixing are found to be comparable with the electronic effects. 

The static and dynamic linear responses, a(0 0) and a( co co), correspond to the so-called static and dynamic polarizabilities, respectively. At second order in the fields, the responses are named first hyperpolarizabilities whereas second hyperpolarizabilities correspond to the third-order responses. Different phenomena can be distinguished as a function of the combination of optical frequencies. So, p(0 0,0), p(—co co,0), p(0 o), — ea), and p(— 2co co,co) are associated with the static, dc-Pockels (dc-P), optical rectification (OR), and second harmonic generation (SHG) processes whereas y(0 0,0,0), y(- ( ( ,0,0), y( 2co co,( ,0), y( co co, — ca, ), and y(— 3 , , ) describe the static, dc-Kerr, electric-field-induced second harmonic generation (EFISHG), degenerate four-wave mixing (DFWM),... 

Kirtman and Luis" have presented a simple extension of their Finite Field-Nuclear Relaxation procedure for calculating the vibrational nonlinear optical contributions to the Degenerate Four-Wave Mixing or Intensity-Dependent Refractive Index process and have illustrated it by application to the water molecule at both HF and MP2 levels of approximation. This approach, which is based on the idea of substracting the unwanted electric dipole terms, enables to go beyond the simple double harmonic approximation, used so far for DFWM." ... 

Several of the third-order nonlinear effects described in section 4.1.3 can be used to characterize bulk materials. Degenerate four-wave mixing (DFWM) is used for measuring third-order properties of films and solutions [43-45], and though this experiment is complex to set up and interpret, it can give valuable information on the magnitude, sign and speed of the nlo process, as well as an indication of the nature of the excitation process. Results from DFWM can be found in section 4.3. Optical Kerr effect (OKE) [46] and electrical Kerr effect (EKE) [47] measurements have also been used to characterize third-order properties of nlo polymers. It is important to note that THG, DFWM, OKE and EKE all measure different parts of the third-order susceptibility, and... 

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