The third-order optical nonlinearity of Bi_3.25La _0.75Ti₃O₁₂ ferroelectric thin film on quartz

Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin film was prepared on quartz substrates using chemical solution deposition. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility χ⁽³⁾ of the BLT thin film have been determined by the Z-scan technique performed at 800 nm with a femtosecond laser. The nonlinear refractive index coefficient γ and the nonlinear absorption coefficient β of the BLT thin film are - 1.915 × 10^{- 12} cm² / W and - 6.764 × 10^{- 8} m/W, respectively, the real part and imaginary part of the third-order nonlinear susceptibility χ⁽³⁾ of the BLT thin film are - 5.81 × 10^{- 18} m² / V ² and - 1.31 × 10^{- 18} m² / V², respectively. Both the real and the imaginary parts of the third-order nonlinear susceptibility χ⁽³⁾ contribute to the nonlinearity of the film. These experimental results show that BLT thin film is a promising material for applications in nonlinear optical devices.