Probing wave packet motion of D₂⁺ with sub femtosecond resolution

In order to achieve better time resolution in pump-probe experiments, it is generally assumed that one must reduce the time duration of two laser pulses. This assumption is not correct. We show that sub-femtosecond time resolution can be achieved even using 50 fsec laser pulses. The key idea is the correlated formation of electron and vibrational wave packet by strong laser field. Here the electron probes the motion of vibrational wave packet. We demonstrate this technique by measuring the vibrational wave packet motion of D₂⁺, on the time scale of 1.5-4.5 fs.