Studies of resonant and preresonant femtosecond degenerate four-wave mixing in unoriented conducting polymers

Degenerate four-wave mixing with femtosecond time resolution is used to measure the magnitude and transient response of the third-order nonlinear optical susceptibility χ⁽³⁾ (ω;ω,-ω,ω) at 620 nm in nonoriented conducting polymers including polydiacetylene, <m1;38p>polyacetylene, polyaniline, polydiethynylsilane, polythiophene, and polythiophene derivatives. <m1;40p>Resonant and nonresonant excitations influence the magnitude and transient response of χ⁽³⁾. <m1;39p>The electronic response is instantaneous for preresonant excitation, but for resonant excitation it <m1;38p>has ultrafast and slow components which illustrate photoexcitation dynamics. The <m1;38p>magnitude of χ⁽³⁾ for all of the polymers is in the range from 10^-10 to 5×10^-8 esu depending on the energy difference between the laser excitation and the polymer absorption maximum.