Ultrafast and large third-order optical nonlinearity of porous nanosized poly-crystal LiNbO3 film

The porous nanosized poly-crystal LiNbO3 film on the fused SiO2 substrate was prepared by using r.f. sputtering method. The microstructure and the third-order optical nonlinearity of the film were investigated. The size of the micro-crystal grains was in the range of 110–160 nm, and the average pore size was 80 nm. The magnitude of ultrafast response χ (3) of the sputtered thin LiNbO3 film at 830 nm wavelength was estimated to be as large as 1.9 × 10 −8 esu, which is 4 orders of magnitude larger than that of LiNbO3 single crystal.