Thermal evaporated Te-Bi2Te3 alloy thin film and its nonlinear optical properties

Te-Bi 2 Te 3 alloy thin film has grown on silicon dioxide substrate by thermal evaporation technique. The Bi 2 Te 3 rhombohedral structure enriched Te in the prepared thin film was identified by high solution transmission electron microscopy (HRTEM), X-Ray diffraction (XRD), Raman spectrum and X-ray photoelectron spectroscopy (XPS). Interestingly, the Te-Bi 2 Te 3 alloy thin film presents a changeover from saturable absorption (SA) to reverse saturable absorption (RSA) as continuously increasing the input intensity, which has been investigated using the open-aperture (OA) z-scan measurement under a femtosecond-pulsed laser at 800 nm. A high modulation depth of 48.3% and large saturation intensity of 24.1GW/cm 2 of the thin film were obtained. Moreover, a large nonlinear absorption coefficient β of ∼10 3  cm/GW is increased with the input intensity elevated. The research results demonstrate that the Te-Bi 2 Te 3 alloy thin film could be an emerging optical material for saturable absorber in Q-switched or mode-locking fiber lasers at low incident intensity while serve as optical limiter at high incident intensity.