Experimental results (IMAGE)
Caption
Fig. 2. Experimental results. The femtosecond excitation pulses A and B ionize isopropanol molecules, the released electrons are transferred to a localized ground state (cf. Fig. 1(a)) within a few hundreds of femtoseconds. The resulting changes of electric properties are mapped by a pulse in the terahertz frequency range, which probes the excited liquid at different delay times after excitation. (a) Measurement with a single excitation pulse A. The nonlinear signal corresponds to an absorption increase and displays a step-like behavior as a function of delay time, superimposed by coherent oscillations. The step is due to transversal excitations, while the oscillations are caused by longitudinal polarons. (b) Measurement with two excitation pulses A and B. The signal exhibits two steps, which are superimposed by oscillations of identical frequency (red line). The polaron frequency remains unchanged after the second excitation, whereas the step-like response is additive. Black line: Sum of signals from measurements with individual excitation pulses A or B.
Credit
MBI: T. Elsaesser / M. Woerner
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