Ks. Lee et al., 2ND-ORDER NONLINEAR-OPTICAL PROPERTIES AND RELAXATION DYNAMICS OF ALIGNED CROSS-LINKED POLYURETHANES WITH HEMICYANINE-TYPE CHROMOPHORES, Journal of the Optical Society of America. B, Optical physics, 15(1), 1998, pp. 393-400
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.