Abstract :
Summary form only given. The two-photon absorption spectrum of oriented trans-polyacetylene was measured from 0.55 eV to 0.96 eV using nonlinear photothermal deflection spectroscopy. The major two-photon resonance is at 0.55 eV, which places the lowest A/sub g/ state at 1.1 eV, below the B/sub u/ resonance at 1.4 eV; the A/sub g/ resonance is relatively broad, 0.2 eV FWHM. At the 0.55 eV two-photon absorption peak, Im/sub X//sup (3)/(-/spl omega/;/spl omega/,-/spl omega/,/spl omega/)=1.6 x 10 x 10/sup -7/ esu, where Im/sub X//sup (3)/(-/spl omega/;/spl omega/,-/spl omega/,/spl omega/) is the imaginary part of the third order nonlinear optical susceptibility. In the technologically important fiber transmission window at 1.3 /spl mu/m, the nonresonant Im/sub X//sup (3)/(-/spl omega/;/spl omega/,-/spl omega/,/spl omega/)=5.2 x 10/sup -9/ esu. There is an additional two photon absorption resonance at 0.8 eV; this feature is much narrower (0.03 eV FWHM) than the 0.55 eV resonance. The large parasitic two photon absorption susceptibility suggests that parallel (four wave mixing) optical architectures may be the most practical route to third order nonlinear optical devices made from conjugated polymers.
