Influence of electric field on SHG properties of LN/PMMA nanocomposites

Lithium Niobate (LiNbO3; LN) nanoparticles were dispersed into a polymer matrix, poly(methyl methacrylate) (PMMA) to prepare an organic–inorganic hybrid LN/PMMA nanocomposites. When no electric field was applied during dispersion, the polar LN nanoparticles remain randomly oriented in the PMMA and unpoled nanocomposite is obtained. In this work, poled LN/PMMA nanocomposites were prepared by applying an electric field of varying strength and used to investigate its influence on the second harmonic generation (SHG) properties (λ = 532 nm) using the fundamental laser (λ = 1064 nm). Since the electric field orients the dipoles of the LN nanoparticles inside the PMMA matrix in the direction of the field, a maximum was observed in the SHG signal as a function of electric field strength. The SHG from the differently poled nanocomposite was investigated as a function of LN nanoparticle concentration, fundamental laser energy, and sample thickness. The trend in SHG is explained and the role of induced and spontaneous polarizations in the SHG generation has been specifically highlighted. It has been observed that the effect of electric field on the SHG properties of the nanocomposite was observed only when the factors contributing to the loss of SHG signal are insignificant.