Nonlinear absorption of Sb-based phase change materials due to the weakening of the resonant bond

摘要

The current study proposes a model based on the weakening of the resonant bond to explore the giant optical nonlinear saturable absorption of Sb-based phase change materials. In order to analyze the weakening of resonant bond effectively, we take the Sb_2Te_3 as an example. First-principle calculations show that both the Born effective charge and optical dielectric constant of crystalline Sb_2Te_3 in the 300 K to 500 K temperature range monotonically decrease with the temperature, indicating a weakening of the resonant bond. This weakening induces a decline in the absorption coefficient at a rate of 10~3m~(-1) K~(-1), which results in a nonlinear saturable absorption coefficient in the order of 10~(-2) m/W. The nonlinear absorption characteristics of the crystalline Sb, Sb_7Te_3, and Sb_2Te_3 thin films at 405 nm laser wavelength are measured via z-scan technique using nanosecond laser pulses to validate the above-proposed model. The experimental results are in good agreement with theoretical prediction.