Two-photon absorption and ultrafast optical computing

The two-photon absorption spectrum of oriented trans-polyacetylene was measured from 0.55 eV to 0.96 eV using photothermal deflection. The lowest lying Ag state is at 1.1 eV, below the 1.4 eV Bu state. The two-photon absorption susceptibility rules out waveguiding devices in trans-polyacetylene; by extension the two-photon absorption coefficient in other materials containing conjugated backbones should be measured before attempting fabrication of waveguide devices. An alternative approach to ultrafast optical computing is presented that uses spatially modulated four wave mixing to get around the problem of large two-photon absorption.