Z-scan measurements of nonlinear absorption and nonlinear refractive index for PVD-grown CoTe₂ thin film

This study investigated the nonlinear optical properties of cobalt ditelluride (CoTe₂) thin films synthesized via physical vapor deposition (PVD). The fabricated CoTe₂ films, with a thickness of approximately 80 nm, exhibited high compositional uniformity. Based on these characteristics, open-aperture (OA) and closed-aperture (CA) Z-scan measurements were performed at 1560 nm and 1910 nm to determine the nonlinear absorption coefficient (β) and nonlinear refractive index (n₂), respectively. The experimental results revealed pronounced intensity-dependent saturable absorption and self-defocusing behavior, with a clear third-order nonlinear response observed at both wavelengths. Specifically, β = ∼-1.16 × 10⁴ cm/GW and n₂ = ∼-1.28 cm²/GW were obtained at 1560 nm, while β = ∼-13.9 × 10⁴ cm/GW and n₂ = ∼-0.87 cm²/GW were extracted at 1910 nm.