Nonresonant third-order materials

On the other hand, the nonlinear optical properties of nanometer-sized materials are also known to be different from the bulk, and such properties are strongly dependent on size and shape [11]. In 1992, Wang and Herron reported that the third-order nonlinear susceptibility, of silicon nanocrystals increased with decreasing size [12]. In contrast to silicon nanocrystals, of CdS nanocrystals decreased with decreasing size [ 13 ]. These results stimulated the investigation of the nonlinear optical properties of other semiconductor QDs. For the CdTe QDs that we are concentrating on, there have been few studies of nonresonant third-order nonlinear parameters. 

The components of the third-order nonlinear susceptibility relevant to the CARS process are conveniently subdivided into two terms vibrationally resonant (X, ) and vibrationally nonresonant (Xnr) components. The total response of the material depends on the sum of these two terms ... 

Table 1. Representative Nonresonant Enhanced Values for Prominent Third-Order TT-Conjugated Polymeric Materials...

As previously introduced, we are focusing on the nonresonant OKE where all the laser pulses, excitation, and prohe are characterized by the same frequency not resonant with any material electronic state. In this case the Born-Oppenheimer (B-0) approximation is valid and a simplified expression for the third-order response can be introduced [41] ... 

All the material information measurable in a OKE experiment are contained in the third-order response, introduced in the previous Sect. 2.2.2. When a nonresonant experiment is performed the Bom-Oppenheimer approximation applies and the relevant function becomes tbe material response, TZijki, see (2.14) and (2.17). In the B-0 model, the response function can always be directly connected with the time-dependent correlation function of the quantum linear susceptibility, Xij [41] ... 

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