Photosensitive chalcogenide glasses are very promising materials for pulsed holography, pulsed photolithography and pulsed optical information recording due to their exceptional sensitivity to pulsed light excitation. We present a comprehensive study of the dynamics of the pulse photoresponse of 0.3-1.0 mm thick chalcogenide glassy As 50 Se 50 thin films using a transient-grating method. Both the decrease of transparency and a change of the dissolution rate were recorded after single Nd : YAG and ArF laser pulse and about (1-5) ร 1000 times larger energy was necessary to obtain the same changes using CW radiation. We show that when excited by a short laser pulse, two different time scales behavior and different intensity dependence of short-and long-time scale signals are present: the short-time signal behaves linearly with the input power but the long-time signal behaves quadratically with the input power. Such behavior reflects a fast electronic process followed by a slow structural rearrangement (the after-pulse effect). The obtained data indicate that the strong increase of photosensitivity following a short intense pulsed light excitation is due to a two-photon effect that aids the process of structural rearrangement as when two photons weaken or break the neighboring bonds, the probability of structural transformation increases significantly.