Exceptionally large third-order optical susceptibility in Ag:SrBi_2Nb_2O_9 composite films

摘要

Thin films of SrBi_2Nb_2O_9 with and without the inclusion of Ag nanocrystals were prepared on MgO (001) substrates by alternative pulsed laser ablation of SrBi_2Nb_2O_9 ceramic and Ag metal in a nitrogen atmosphere. The size of the Ag nanocrystals can be brought down to ca. 5.0 run, as revealed by transmission electron microscopy and X-ray diffraction. We measured the third-order susceptibility χ~((3)) of the deposits by single beam z-scan technique at a wavelength of 532 nm. It is found that SrBi_2Nb_2O_9 is an effectively nonlinear optical medium, exhibiting a very large χ~((3)). With the inclusion of Ag nanocrystals the χ~((3)) was nearly doubled (Reχ~((3))=8.052 x 10~(-7) esu, and Imχ~((3))=-1.717 x 10~(-7) esu), which comes very close to the maximum value available in the current time. This indicates that the Ag:SrBi_2Nb_2O_9 composite structure can be an excellent candidate for nonlinear optical applications. A general approach for further enhanced third-order susceptibility by tailoring the dielectric constant of the metal inclusion is briefly discussed.