Third-order optical nonlinearity of the CuCo_0.5Ti_0.5O₂ nanostructure under 120  fs laser irradiation

Recently, titanium-based nanostructures with high nonlinear optical properties have found use in ultrafast photonic system applications. Here, we report a study of the third-order nonlinear optical property of the ${{\rm CuCo}_{0.5}}{{\rm Ti}_{0.5}}{{\rm O}_2}$CuCo_0.5Ti_0.5O₂ (CCoTO) nanostructure synthesized via a simple chemical route. The 40-70 nm CCoTO nanoparticles with centrosymmetric crystalline structure show strong absorption in the 325-850 nm wavelength range due to the presence of different crystalline phases and surface vacancies. A Z-scan technique is used to study the electronic third-order nonlinearity of the synthesized nanoparticles, where a low-repetition-rate 120 fs laser source is employed to minimize thermal agitation-related nonlinearity. The CCoTO nanoparticles possess high surface defects due to oxygen- and copper-related vacancies, which are able to enhance the exciton oscillator strength resulting from the high value of third-order optical nonlinearity. The estimated values of nonlinear refractive index (${n_2}$n₂) and nonlinear absorption coefficient ($\beta $β) of the CCoTO are $ - {1.24}\; \times \;{{10}^{ - 15}}$-1.24×10^-15 and ${3.79} \times {{10}^{ - 11}}$3.79×10^-11, respectively, under ${188}\,\,{{\rm GW/cm}^2}$188GW/cm² incident intensity. The intensity-dependent nonlinear optical property of the synthesized nanoparticles is also studied under different incident laser irradiation (62.7, 93, and ${188}\,\,{{\rm GW/cm}^2}$188GW/cm²). In the two-photon absorption (TPA)-dominated third-order nonlinear optical process, the values of ${n_2}$n₂ and $\beta $β of CCoTO are increased with intensifying the incident laser irradiation. The obtained high value of third-order optical nonlinearity of the synthesized nanostructure can be exploited in optical power limiters, pulse power reshaping, and optical switching applications.