Structure-changed third-order optical nonlinearity in CaCu3Ti4O12 thin films grown on MgO(111) substrates

CaCu3Ti4O12 (CCTO) thin films of preference (220) orientation are deposited on MgO(111) substrates using pulsed laser deposition method. The third-order optical nonlinearity of CCTO films was investigated using Z-scan technique at a wavelength of 532 nm with 25 ps duration pulses. The self-focusing behavior in CCTO films was observed, which is different from the traditional CCTO films grown on LaAlO3 (0001), MgO(100), and fused silica substrates of self-defocusing behavior. The third-order nonlinear refraction coefficient is determined of a value 0.76 cm2/GW, along with the fifth-order nonlinear refractive index -0.2 cm4/GW2, the nonlinear absorption coefficient -1.87 × 10−7 m/W and saturable absorption intensity 1.72 GW/cm2. The structure-changed nonlinear refraction and fast response at picosecond time-domain extend the potential applications of CaCu3Ti4O12 thin films for nonlinear photonics devices.