  In this article, we employed nanosecond Z-scan technique to demonstrate the
nonlinear optical response in Ge30Se55Bi15 thin films after thermal and photo
annealing. The intensity dependent open aperture Z-scan traces reveal that for
all the samples, i.e. as-prepared, thermal and photo annealed thin films
exhibit reverse saturable absorption (RSA). The experimental results indicate
that both thermal and photo annealing can be efficiently used to enhance the
nonlinear absorption coefficient compared to as-prepared sample. We further
demonstrate that beta value of thermally annealed and as-prepared samples
increase significantly at higher intensities. On the contrary, beta for photo
annealed sample does not exhibit appreciable changes against the intensity
variation.
