Nonlinear optical properties of thin films of polysilane

Optical third harmonic generation measurements by transmission have been performed on thin films of polysilane deposited by a spinning technique with a thickness varying between 0.15 and 0.45 μm. The films have a good optical quality and support large laser power (∼200 MW/cm2 at 1.064 μm). They are transparent in visible and near infrared. The measured average value of cubic susceptibility 〈χ(3)xxxx (−3ω; ω,ω,ω)〉 is equal to (1.5±0.1)×10−12 esu at 1.064 μm. The technique used for the third harmonic generation measurements allows determination of both modulus and phase of χ(3). It is argued that the large value of χ(3) is due to a three-photon resonance at 1.064 μm.