Tunable nonlinear optical absorption in amorphous and crystalline Sb2Se3 thin films

Abstract

The nonlinear optical absorption properties of as-deposited and crystalline Sb2Se3 films were systematically studied by using open-aperture Z-scan technique with femtosecond laser pulses at the wavelength of 800 nm. It is interesting to find that the crystallization leads nonlinear optical absorption to switch from reverse saturable absorption to saturable absorption. A tunable behavior is attributed to the competition between ground state excitation and excited state absorption, which depends critically on the facts of band gap energy and the density of localized defect states in the Sb2Se3 film. A three-level approximate model is proposed to explain the probable electronic transition and its rationality is further confirmed by second harmonic experiments under the same conditions. In particular, it is found that there are two different nonlinear optical absorption mechanisms coexisting in one kind of material with identical chemical composition, and their switching behavior is regulated merely by phase-change after thermal treatment. These special properties of Sb2Se3 thin film imply huge potential applications in the field of innovative nonlinear optical devices.