Abstract
Nanosecond near resonant excitation in As50S50 thin films leads to strong nonlinear optical response, i.e. nonlinear absorption coefficient up to 4 × 106 cm GW−1 and nonlinear refractive index of 8.5 cm2 GW−1, both of which are the strongest ever reported in amorphous semiconductors. We propose a three-level energy band model to explain this effect, which indicates that the nonlinear process is reverse saturable absorption in nature, mediated by excited-state absorption from slow interband transition between the conduction and valence band. On the other hand, observation of negative nonlinear refractive index reveals the occurrence of self-defocusing effect. Finally, benefitting from the strong nonlinear response, we demonstrate a promising application of As50S50 thin films as an optical limiter for optoelectronic sensors.
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