Exceptionally large third-order optical susceptibility in Ag:SrBi2Nb209 composite films

Thin films of SrBi2Nb2O9 with and without the inclusion of Ag nanocrystals were prepared on MgO (001) substrates by alternative pulsed laser ablation of SrBi2Nb2O9 ceramic and Ag metal in a nitrogen atmosphere. The size of the Ag nanocrystals can be brought down to ca. 5.0 inn, as revealed by transmission electron microscopy and X-ray diffraction. We measured the third-order susceptibility x(3) of the deposits by single beam z-scan technique at a wavelength of 532 nm. It is found that SrBi2Nb2O9 is an effectively nonlinear optical medium, exhibiting a very large x(3). With the inclusion of Ag nanocrystals the X(3) was nearly doubled (Rex(3)=8.052 x10-7 esu, and /mx(3)=-1.717 x 107 esu), which comes very close to the maximum value available in the current time. This indicates that the Ag:SrBi2Nb2O9 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.