Dispersion relation in the third-order electric susceptibility for polysilane film

The Kramers-Kronig (KK) dispersion relation has been proved to hold between independently measured spectra of the phase shift {φ}({ω}) and the modulus {}{χ}̃ \~⁽³⁾/({ω}){} of third-order electric susceptibility {χ}̃ \~⁽³⁾ (={}{χ}̃ \~⁽³⁾{}e^iφ) for the third-order harmonic generation in silicon-based polymer, poly(dihexylsilane) (PDHS) films, providing a direct experimental substantiation of the reciprocal KK relations in the nonlinear optical solids. The reciprocal dispersion relations have been also found to hold for the real and imaginary parts of {χ}̃ \~⁽³⁾ in PDHS films.