Observation of short-lived laser-dressed quantum states in the frequency plane

We present a method for measuring a complete frequency map of laser-dressed states with femtosecond lifetimes. It is based on collecting decay products as a function of the frequency of the excitation pulse and its delay with respect to the linearly chirped laser pulse, centered at the resonant transition frequency. The method has been tested on the case of laser-coupled 2s2p (1) P-0 and 2p(2) S-1(e) autoionizing resonances in He and is applicable to other quantum systems with short-lived states. When the laser coupling effects are known, the excitation pulse properties can be extracted from the map.