Abstract

The predominant class of molecular systems considered so-far towards applications in the realm of quadratic nonlinear optics has been derived from the all-pervading "molecular diode" template as exemplified by paranitroaniline-like molecules. The underlying basic paradigm consists in the dipolar anchoring of an interacting couple of electron donor and acceptor groups to a conjugated π electron linkage⁽¹⁾. The virtue of such a configuration is to provide a significant electronic charge displacement in the ground state which is further enhanced upon directional optical excitation towards the charge-transfer level. This basic mechanism has been confirmed by nearly two decades of experiments in solutions, crystals and polymer media with the two-level quantum model providing solid theoretical support⁽²⁾. Both the Electric Field Induced Second Harmonic (EFISH) experiment and the current poled polymer technology essentially depend on the existence and magnitude of a strong ground state dipole μ contributing to the μ.E coupling potential between individual molecules and the externally applied de poling field E.

© 1995 Optical Society of America