The timehyphen;resolved nonlinear transmission of bulk egr;hyphen;GaSe has been studied in the femtosecond regime when resonantly exciting the material in the vicinity of the exciton at room temperature. Two regimes are evidenced. At early time delay, a blue shift of the exciton with no linewidth broadening can be related to optical Stark effect, while at longer time delay the usual exciton screening and bandhyphen;gap renormalization due to real electronic transitions is observed. At resonance, a dependence of the Stark shift with the amplitude of the exciting field is obtained, as predicted by a simple lsquo;lsquo;dressedhyphen;atomrsquo;rsquo; model.
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