Exceptionally large third-order optical susceptibility in Ag:SrBi2Nb2O9 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 nm, 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 SrBi₂Nb₂O₉ 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 × 10^− 7 esu, and Imχ⁽³⁾ = − 1.717 × 10^− 7 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.