Strong two-photon absorption in ErFeO3 thin films studied using femtosecond near-infrared Z-scan technique

Abstract

Ultrafast nonlinear optical (NLO) characterization of ErFeO3 thin films deposited by the solgel assisted spin coating technique is reported herein. In the present investigation, we have used femtosecond (fs) pulses for studying the nonlinear absorption and refraction properties of ErFeO3 thin films. Intensity dependent open and closed aperture Z-scan experiments were performed on ErFO3 films in the visible and near-infrared wavelengths of 600 nm, 800 nm, and 1200 nm. To explain the observed NLO results, phenomenological models of simultaneous multi-photon and excited sate absorption are developed for three-level model systems suitable for excitation wavelengths with (600 and 800 nm) and without (1200 nm) linear absorption, respectively. Optical limiting (OL) characteristic is shown to exist through the phenomenon of two-photon absorption in a certain intensity range at the three wavelengths and under the simultaneous saturation of linear absorption at 600 nm and 800 nm. The upper limit of the intensity for OL applications is demonstrated by the saturation effect. The non-linear absorption results are correlated with the linear absorption at these wavelengths, which involves electronic transitions between Fe d- and O p-orbitals.