Origin of the giant optical nonlinearity of Sb_2Te_3 phase change materials

摘要

We report the giant optical nonlinear absorption and refraction of Sb_2Te_3 phase change materials at low laser irradiation intensities. The nonlinear absorption and refraction coefficients reach up to -6.63 × 10~(-2) m/W and 2.606 × 10~(-9) m~2/W, respectively. The first principles calculation indicates that the giant nonlinear absorption stems from the band filling effect of the photon induced free carriers under laser irradiation. The band-gap shrinking results in a positive thermo-optic coefficient, thus the giant nonlinear refraction. The numerical results are generally correlated with the experimental findings from z-scan and temperature-variable ellipsometric measurements.