Investigation Of Optical Non-Linearity Of Lead-Free Ferroelectric Potassium Sodium Niobate (K0.35na0.65nbo3) Thin Films Via Two-Wave Mixing Phenomenon

In the present work, structural, morphological and optical properties of lead- free ferroelectric Potassium Sodium Niobate (K0.35Na0.65NbO3 or KNN) films (similar to 1 mu m thin), grown using pulsed laser deposition (PLD) technique at distinct substrate temperature, have been studied. The bandgap and the refractive index value of KNN thin films at different substrate temperatures (700-800 degrees C) are found to be in the range of 3.6-4.0 eV and 2.14-2.37 respectively. The refractive index dispersion of KNN films has been fitted using Wemple- DiDomenico's single oscillator model. Two-wave mixing phenomenon has been exploited via pump-probe technique to investigate the non-linear optical property of KNN thin films having gold microdisks at the surface. The periodic transmission pattern of probe intensity evidently signifies the non-linear optical behaviour of the KNN thin films. The enhancement in the probe beam intensity when the pump beam is kept unblocked indicates the exchange of energy between the pump and probe beams. The non-linear optical response in KNN film is also attributed to the orientation of ferroelectric domains in the direction of the net electric field, along with the occurrence of surface plasmon (SP) modes resulting in the stronger coupling of the pump and probe beams.