Electronic polarizability and third-order susceptibility of spray-deposited α-Fe ₂ O ₃ :Ca thin films

Thin films of undoped and calcium-doped iron oxide ([Formula: see text]: 0, 2, and 5 at.%) were prepared via spray pyrolysis on glass substrates heated to [Formula: see text]C. The influence of Ca as a doping agent on the structural, morphological, and nonlinear optical (NLO) properties was investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), optical transmission measurements, and third harmonic generation (THG). XRD confirmed the formation of the rhombohedral hematite phase ([Formula: see text]-[Formula: see text]) with a preferential (104) orientation, AFM revealed that 5 at.% [Formula: see text]-doped films exhibited the lowest surface roughness ([Formula: see text][Formula: see text]nm, [Formula: see text][Formula: see text]nm). A strong correlation between reduced surface roughness and enhanced electronic polarizability was observed, with the [Formula: see text] at.% Ca-doped [Formula: see text]-[Formula: see text] thin films showing the highest polarizability and a pronounced NLO response. The third-order NLO susceptibility [Formula: see text] was measured at a wavelength of 1,064[Formula: see text]nm and found to be [Formula: see text][Formula: see text]esu. These findings indicate that the prepared thin films are promising candidates for NLO applications.