Solution 4 Four Wave Mixing Experiments

Trimethylsilyl-end-substituted oligothiophenes up to the octamer were studied in THF solution by Cheng et al. with THG experiments [285]. They found a considerably smaller change in y with a power of 2.8 without any evidence for saturation which they attributed to differences between THG and four-wave mixing with EFISH experiments (see above). 

The main advantage of the phase-modulated pulse is its capability of having very broad spectrum in a controlled manner. A preliminary experiment of four-wave mixing in dye solutions has been tried in our group using a broad-band chirped pulse produced in an optical fiber, and confirmed the achievement of subpicosecond resolution time much shorter than the pulse width, though T2 is too short to be observed. 

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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