Nonlinear optical properties of arsenic telluride and its use in ultrafast fiber lasers.

We report the first investigation results of the nonlinear optical properties of As ₂ Te ₃ . More specifically, the nonlinear optical absorption properties of the prepared α-As ₂ Te ₃ were investigated at wavelengths of 1.56 and 1.9 μm using the open-aperture (OA) Z-scan technique. Using the OA Z-scan technique, the nonlinear absorption coefficients (β) of α-As ₂ Te ₃ were estimated in a range from (- 54.8 ± 3.4) × 10 ⁴  cm/GW to (- 4.9 ± 0.4) × 10 ⁴  cm/GW depending on the irradiance of the input beam at 1.56 μm, whereas the values did from (- 19.8 ± 0.8) × 10 ⁴  cm/GW to (- 3.2 ± 0.1) × 10 ⁴  cm/GW at 1.9 μm. In particular, the β value at 1.56 μm is an order of magnitude larger than the previously reported values of other group-15 sesquichalcogenides such as Bi ₂ Se _3, Bi ₂ Te _3, and Bi ₂ TeSe ₂ . Furthermore, this is the first time report on β value of a group-15 sesquichalcogenide at a 1.9-μm wavelength. The density functional theory (DFT) calculations of the electronic band structures of α-As ₂ Te ₃ were also conducted to obtain a better understanding of their energy band structure. The DFT calculations indicated that α-As ₂ Te ₃ possess sufficient optical absorption in a wide wavelength region, including 1.5 μm, 1.9 μm, and beyond (up to 3.7 μm). Using both the measured nonlinear absorption coefficients and the theoretically obtained refractive indices from the DFT calculations, the imaginary parts of the third-order optical susceptibilities (Im χ ⁽³⁾ ) of As ₂ Te ₃ were estimated and they were found to vary from (- 39 ± 2.4) × 10 ^-19 m ² /V ² to (- 3.5 ± 0.3) × 10 ^-19 m ² /V ² at 1.56 μm and (- 16.5 ± 0.7) × 10 ^-19 m ² /V ² to (- 2.7 ± 0.1) × 10 ^-19 m ² /V ² at 1.9 μm, respectively, depending on the irradiance of the input beam. Finally, the feasibility of using α-As ₂ Te ₃ for SAs was investigated, and the prepared SAs were thus tested by incorporating them into an erbium (Er)-doped fiber cavity and a thulium-holmium (Tm-Ho) co-doped fiber cavity for both 1.5 and 1.9 μm operation.