Nanosecond pulse triggered absorption modulation in a-As50Se50 chalcogenide thin films

We present strong absorption modulation (ΔA ≈ 3.5%) in As50Se50 chalcogenide thin film, using nanosecond pulses, as a new tool to tune the optical absorption spectrum in bandgap and sub-bandgap region. Interestingly, observed change in absorption persists only for few microseconds and thus allows modulating the absorption in a very short time scale. In our experiments, As50Se50 thin films were irradiated by 532 nm laser having a pulse width of 5 ns (control beam) with very low energy fluency of 3 mJ/cm2 to modulate the absorption spectrum of as prepared As50Se50 thin film. Modulation of the sample absorption was monitored in the time window of 1 ns–200 μs using a probe beam in the wavelength range of 500 to 800 nm, which covers the bandgap and sub-bandgap region of the sample. Absorption changes were observed to be largest (ΔA ≈ 3.5%) in the wavelength range 550–700 nm which decays very fast. a-As50Se50 thin films were found to exhibit full reversibility in transmission post-pulse-excitation, an observation that is unusual in chalcogenide systems.