Asymmetric two-beam coupling with high optical gain and high beam diffraction in external-electric-field-free polymer composites

This paper presents high-performance asymmetric two-beam coupling, beam diffraction and holographic recording in polymeric composites without poling and applying an external electric field. The polymer composites are based on poly(2-(9carbazoyl)ethyl methacrylate) (PCzEMA) and poly(N-vinyl carbazole) (PVCz) as host matrices with 2,4,7-trinitro-9fluorenone (TNF) as a sensitizer, four kinds of plasticizer; tricresyl phosphate (TCP), n-butyl benzyl phthalate (BBP), diphenyl phthalate (DPP), and dicyclohexyl phthalate (DCP); and (s)-(-)-1-(4-nitrophenyl)-2-pyrrolidine-methanol (NPP) as a nonlinear optical dye. The gain coefficient and diffraction efficiency increased markedly with increasing TNF and NPP concentrations. The highest net gain coefficient of 101.9cm(-1) with optical gain of 224cm-1 and absorption coefficient of 122.1 cm(-1) was obtained for PVCz/NPP/DDP/TNF (35/20/40/5), and the highest diffraction efficiency of 88% was achieved for PCzEMA/NPP/TCP/,rNF (35/30/30/5) and PVCz/NPP/DDP/TNF (35/20/39/6) composites. The BBP plasticizer significantly enhanced the speed of two-beam coupling and diffraction grating formation for both PVCz and PCzEMA composites. Holographic images stored in the polymer composites were clearly read out using a probe beam. The key point for achieving the external -electric-field-free high performance of asymmetric energy transfer and diffraction efficiency is to have a high concentration of TNF (5 or 7 wt%).