Second-harmonic light generation in pyroelectric liquid-crystal polymers

Pyroelectric liquid-crystal polymers were prepared by photopolymerization of binary mixtures of two monomers that exhibit a smectic C* phase: A2c, 49-$(R)-(2)-2-[(10-acryloyloxy)decyl]oxy%-3-nitrophenyl 4-{48[(11-acryloyloxy)undecyloxy]phenyl%benzoate and A1b, 49-((R)-(1)-2-octyloxy)-39-nitro phenyl 4-(48-@(11acryloyloxy)undecyloxy]phenyl) benzoate. Both liquid-crystal monomers have a NO2 substituent to enhance the nonlinear optical properties, and one of the monomers, A2c, permits polymerization to a cross-linked polymer. During the polymerization an electric field of approximately 25–50 V/mm was applied over the ferroelectric liquid-crystal cells. All cases of polymers formed from the chiral smectic C* phase showed a secondharmonic-generated signal with no external field present, indicating that polar order became fixed. The orientation dependence of the second-harmonic-generated intensity was similar to that of the ferroelectric liquid-crystal monomer; however, some changes were observed that might be due to changes in the dielectric axes of the system. The highest d16 and d23 coefficients were found to be in the range 0.65–0.8 pm/V and differed depending on the detailed preparation of the sample. Experimental results of several polarization combinations of the pump and frequency-doubled light are presented and discussed. © 1998 Optical Society of America [S0740-3224(98)01202-8] OCIS codes: 190.4160, 160.3710, 160.2100, 160.5470.