Enhanced Ultrafast Nonlinear Optical Response in Ferrite Core/Shell Nanostructures with Excellent Optical Limiting...

Nonlinear optical nanostructured materials are gaining increased interest as optical limiters for various applications, although many of them suffer from reduced efficiencies at high-light fluences due to photoinduced deterioration. The nonlinear optical properties of ferrite core/shell nanoparticles showing their robustness for ultrafast optical limiting applications are reported. At 100 fs ultrashort laser pulses the effective two-photon absorption (2PA) coefficient shows a nonmonotonic dependence on the shell thickness, with a maximum value obtained for thin shells. In view of the local electric field confinement, this indicates that core/shell is an advantageous morphology to improve the nonlinear optical parameters, exhibiting excellent optical limiting performance with effective 2PA coefficients in the range of 10^-12 cm W^-1 (100 fs excitation), and optical limiting threshold fluences in the range of 1.7 J cm^-2 . These values are comparable to or better than most of the recently reported optical limiting materials. The quality of the open aperture Z-scan data recorded from repeat measurements at intensities as high as 35 TW cm^-2 , indicates their considerably high optical damage thresholds in a toluene dispersion, ensuring their robustness in practical applications. Thus, the high photostability combined with the remarkable nonlinear optical properties makes these nanoparticles excellent candidates for ultrafast optical limiting applications.