Nonlinear Ground State Fluctuations (Zero Point Motion) as the Source of χ(3) in Polyacetylene

Abstract

For a deeper understanding of the nonlinear optical response of conjugated polymers, the connection between the nonresonant response to pumping well below the absorption edge and the resonant response to pumping into the absorption band must be developed. For trans -(CH)X, resonant pumping causes photogeneration of charged solitons; the resulting shifts in oscillator strength lead to relatively large changes in the optical constants. We generalize to the nonresonant regime where the nonlinear response arises from virtual soliton-antisoliton (SS) pairs and is enabled by nonlinear ground state fluctuations, or "instantons".