  The nonlinear polaronic response of electrons solvated in liquid 2-propanol
is studied by two-dimensional terahertz spectroscopy. Solvated electrons with a
concentration of c$_e \approx$ 800 $\mu$M are generated by femtosecond
photoionization of alcohol molecules. Electron relaxation to a localized ground
state impulsively excites coherent polaron oscillations with a frequency of 3.9
THz. Off-resonant perturbation of the THz coherence by a pulse centered at 1.5
THz modifies the polaron oscillation phase. This nonlinear change of electron
polarizability is reproduced by theoretical calculations.
