2ND-ORDER NONLINEAR-OPTICAL PROPERTIES AND RELAXATION DYNAMICS OF ALIGNED CROSS-LINKED POLYURETHANES WITH HEMICYANINE-TYPE CHROMOPHORES

Three types of different cross-linked polyurethane were prepared by th e reaction of poly[(phenylisocyanate)-co-formaldehyde] with three diff erent hydroxy-functionalized nonlinear optical chromophores. For poled and cured polymers the chi((2)) values were between 16.8 and 37.4 pm/ V, measured at a wavelength of 1.064 mu m. Thermal stability studies p erformed on a sample having bonding sites of vertical-parallel structu re between the chromophore and the liquid polymer matrix indicated, by second-harmonic-generation activity, a minimum decay of the chi((2)) value owing to lattice hardening of the polyurethane matrix with three bonding sites. The relaxation times of aligned dipoles in vertical-pa rallel polyurethane were measured by variation of poling and cross-lin king conditions. Three decay modes were found to exist: the mode that corresponds to partially bonded or free unbonded chromophores, the mod e of thermal relaxation of bonded chromophores, and the mode that is d ue to the relaxation of an elastically stressed main chain induced by the poling elastic field. (C) 1998 Optical Society of America.