# Multipath Data Storage by Third-Order Nonlinear Optical Properties in Zinc Oxide Nanostructures
## 3 Results
### Multipath Load Balancing Assisted by Nonlinear Optical Properties  
In order to explain the drastic increase in the nonlinear optical response derived by the laser annealing process in the sample, we identified that the modification in optical losses automatically changes the nonlinear response. The distribution of the nanostructures in the film is random but the collective third-order optical nonlinearities are dependent on radiative and non-radiative processes. In this regard, we clearly noticed changes in UV-vis spectra by laser annealing. Changes in morphology or structure in the film measured by TEM and XRD techniques were not observed. However, it can be expected that the removal of defects can be obtained by laser annealing regarding the observed modification in the multiphotonic transitions of the film. The third-order nonlinear optical response exhibited by a nonlinear system is dependent on atomic dipole moment. Formation and elimination of localized electronic states induced by thermodynamic passivation of ZnO surfaces has been reported [26]. Then magnetic techniques seem to be suitable for revealing with high sensitivity changes in electronic bonds by the incorporation of removal of defects. We describe \(\chi^{(3)}\), considering a nanosecond radiation with optical frequency \(\omega\), and a detuning of frequency represented by \(\Delta=\omega-\omega_{21}\), then [27]  
\[\chi^{(3)}=\frac{4 Nm^{4}\Big{[}T_{1}T_{2}^{2}(\Delta T_{2}-i)\Big{]}}{3\hbar^{ 3}\Big{[}1+\Delta T_{2}^{2}\Big{]}^{2}}. \tag{6}\]  
In Equation (6), \(N\) describes two-level atoms per unit volume, \(\hbar\) describes the Planck constant, \(m\) is associated with the atomic dipole moment, \(1/T_{1}\) describes the population loss through radiative and non-radiative processes of the upper quantum level of excitation, and \(1/T_{2}\) describe the dynamics of a two-level system with a characteristic rate of polarization loss. In our studied case, the laser annealing seems to derive in a modification in the multiphotonic transitions of the film. In the limit of large detunings, i.e., \(\Delta T_{2}\gg 1\), it can be considered that [27]  
\[\text{Re}\chi^{(3)}\approx\frac{4}{3}Nm^{4}\bigg{[}\frac{1}{\hbar\Delta}\bigg{]} ^{3}\frac{T_{1}}{T_{2}}. \tag{7}\]  
In addition, the same consideration can be obtained [28],  
\[\text{Im}\chi^{(3)}\approx-\frac{4}{3}Nm^{4}\bigg{[}\frac{1}{\hbar\Delta}\bigg{]} ^{3}\frac{T_{1}}{\Delta T_{2}^{2}}. \tag{8}\]  
Regarding that no modification in nanostructured morphology of the samples was obtained after the optical irradiation, the changes in both refractive and absorptive nonlinearities are not suitable to be described by \(N\) or \(m\) in this model. On the other hand, small modifications related to changes in \(\Delta\) or in population losses can generate a strong enhancement in the third-order optical nonlinear properties. In a non-resonant regime, as is our case, the radiative spontaneous emission and the decay due to phonons could be promoted by inhibition of defects in the nanostructures, and these conditions must be more important in respect to the non-radiative spontaneous emission of the atoms. This consideration as a function on the modification of the loss factor \(T_{1}/T_{2}\) is shown in Figure 6.  
We consider an XOR operation in order to identify binary data recorded in the sample. An exclusive-OR logic gate generates a logical zero if the operands are assumed to be identical; otherwise, a logical value equal to one is obtained. In this work, the operation principle underlying this function was proposed to be by two different paths; these channels correspond to the separated evaluation of the real and imaginary part of \(\chi^{(3)}\), measured by a standard two-wave mixing. The encrypted signals correspond to the nonlinear optical parameters related to the fingerprints of the sample studied. The encryption method is proposed to be made by a systematic modification in particular regions of the film sample.