High refractive nonlinearity of PdO films under femtosecond 800 nm laser pulses

Abstract

Nonlinear optical properties of thin polycrystalline PdO films are investigated using the Z-scan technique and a 800 nm 180 fs laser, whose wavelength is significantly longer than the absorption edge at 500 nm. Cubic nonlinear susceptibility Re χ(3) = +1.1 × 10−6 esu (n2 = 5.6 × 10−9 cm2/W) and nonlinear absorption coefficient β ≈ 5 × 10−5 cm/W are determined. The positive sign of Re χ(3) implies intraband carrier (predominantly holes) relaxation dynamics and the optical Kerr effect as underlying mechanisms. Relaxation time of refractive nonlinearity is estimated in the picosecond range. Linear absorption spectra in the interval of 1.5–6 eV, compared with the literature data, suggest that microcrystals in our films are predominantly oriented with the С axis orthogonal to the film.