Cubic Susceptibility of Polythiophene Solutions and Films

Cubic susceptibility of poly(butyl)thiophene has been studied by optical third harmonic generation (THG) in solution and in solution cast thin film as a function of fundamental wavelength. The thin film data have been obtained in the polymer absorption range for harmonic wave and show existence of a large three photon resonance. For polymer solutions the THG measurements have been done at 1.064 and 1.907 μm fundamental wavelength. At 1.907 μm the cubic susceptibility is complex with negative real part whereas at 1.064 μm it is real and positive. The observed large three photon resonance is interpreted as a consequence of inhomogenous one photon absorption broadening.