Cu-engineered TiO₂ thin films: defect-driven nonlinear optical responses for ultrafast frequency conversion and...

Area of Science:

• Materials Science
• Optics
• Nanotechnology

Background:

• Titanium dioxide (TiO2) is a versatile material with applications in optics.
• Investigating dopant effects on TiO2's nonlinear optical (NLO) properties is crucial for advanced photonic devices.

Purpose of the Study:

• To explore the impact of copper (Cu) doping on the NLO characteristics of TiO2 thin films.
• To determine the optimal Cu concentration for enhanced NLO responses.

Main Methods:

• Fabrication of Cu-doped TiO2 thin films using spray pyrolysis.
• Characterization using X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS).
• Nonlinear optical measurements including Z-scan, second-harmonic generation (SHG), third-harmonic generation (THG), and Maker fringe technique.

Main Results:

• XRD and XPS confirmed successful Cu incorporation into the anatase TiO2 lattice.
• An intensity-dependent transition from saturable to reverse saturable absorption was observed.
• The 2 wt% Cu-TiO2 film showed the highest nonlinear absorption and third-order nonlinear susceptibility (χ(3) = 3.85 × 10⁻²¹ m² V⁻²).
• Enhanced THG performance was noted for Cu-doped films under picosecond excitation.

Conclusions:

• Cu doping significantly enhances the NLO properties of TiO2 thin films.
• The observed improvements are linked to Cu-induced defect states and lattice distortions.
• Cu-TiO2 thin films are promising materials for optical limiting and ultrafast frequency conversion applications.