Ellipsometric and third-order nonlinear optical studies of pulsed laser deposited aluminium doped zinc oxide thin films

Abstract

In the present work, an attempt is made to study the optical properties of aluminium doped zinc oxide (AZO) thin films fabricated by pulsed laser deposition (PLD) technique at different laser fluences. The non-polar ‘a-plane’ orientation of the AZO nanostructure is confirmed by x-ray diffraction technique. The linear optical parameters such as refractive index (n), extinction coefficient ( k ), and dielectric constants ( ε ) are studied by spectroscopic nulling ellipsometer. An increase in extinction coefficient with increase in wavelength is observed. This rare phenomenon is observed for the film prepared at highest laser fluence. The nonlinear optical properties of prepared AZO thin films are evaluated by employing an open aperture (OA) and a closed aperture (CA) Z-scan measurements at a continuous 532 nm wavelength laser source. The presence of reverse saturable absorption (RSA) is observed in all the films; which is attributed to the two-photon absorption mechanism. CA measurements revealed, a switching behaviour from self-de-focusing to a self-focusing mechanism. Third-order nonlinear optical susceptibility, χ ( 3 ) values of AZO films are found be in the order of 10 −6 e.s.u . Further, a-plane oriented AZO films showed optical limiting behaviour with promising optical threshold value (2.964 kJ/cm 2 ) .