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Chalcogenide glasses (ChG) consist of group six elements except oxygen as major constituent, are an important class of amorphous semiconductors distinguished itself from other inorganic amorphous semiconductors by their unique photosensitivity depicted in terms of chemical, physical and structural changes upon bandgap/sub-bandgap illumination. Light induced shift in optical absorption of ChG is a well studied phenomenon over many decades. Examples of such effects are photodarkening (PD) and photobleaching (PB) in As and Ge based chalcogenides respectively. In our recent work, we have demonstrated for the first time an unusual coexistence of PD and PB in Ge-As-Se thin film. Moreover, these effects are found to be compositionally tunable and exhibits a composition dependent crossover from PD to PB. Interestingly, it has been shown that for short illumination with a continuous wave light, transient part is more apparent than the slow and cumulative metastable part. In this context, we report the first observation of nanosecond light induced thermally tunable transient dual absorption bands, one in the bandgap (TA1) and the other in the sub-bandgap (TA2) regions of a-Ge-As-Se thin films. Further, rigidity dependent transient absorption study provides the first direct evident of network rigdity theory for pulsed illumination. |