Researchers at Shanghai Institute of Optics and Fines Mechanics (SIOM/China) observed the intensity-dependent nonlinear absorption reversal of c-GST and obtained the effective nonlinear absorption coefficient with an order of10-2m/W. [JOURNAL OF APPLIED PHYSICS 110, 033503 (2011)]

The intensity-dependent nonlinear absorption characteristics of c-GST thin films are measured by z-scan method. The results show that the nonlinear absorption coefficient is at the order of 10-2 m/W. At the laser intensity of lower than 0.17 GW/m2, the c-GST thin films suggest nonlinear saturable absorption, and the nonlinear absorption response exhibits reverse-saturable absorption when the laser intensity is higher than 0.17 GW/m2. In combination of the absorption spectra, variable-temperature ellipsometric spectroscopy and picosecond z-scan measurement with density functional theory and numerical calculations, the mechanism responsible for the nonlinear absorption is discussed. The analysis indicates that at the low laser intensity, the nonlinear saturable absorption mainly stems from band-filling effect,although thermal effect also plays an important role. At the high laser intensity, the nonlinear reverse-saturable absorption is attributed to thermal-induced absorption increment.