χ⁽³⁾ of M-X chains

The third-order nonlinear optical susceptibility has been investigated for oriented thin films of halogen bridged platinum complexes. The | χ (3)(−3ω;ω,ω,ω) | of a σ-conjugated polysilane, poly(di-n-hexylsilane) (PDHS), by means of third-harmonic generation (THG) measurement, in the fundamental photon energy region from 0.56 eV to 2.15 eV. The obtained | χ ⁽³⁾(−3ω;ω,ω,ω) | spectrum associated with the third harmonic generation (THG) was measured by the Maker fringe method in the region of fundamental wavelength 0.6µm~lµm and 1.6µm~2.2µm. In the | χ⁽³⁾ | spectra, we found a peak structure at ω ~ 1.8eV that is attributable to a two-photon resonance to the optically forbidden charge transfer exciton. The | χ⁽³⁾ | value was in the order of 10⁻¹¹esu that is comparable to the π-conjugated polymers. Common features of NLO processes for the one-dimensional semiconductors are discussed.