Observing the attosecond dynamics of nuclear wavepackets in molecules by using high harmonic generation in mixed gases

We probe the attosecond dynamics of nuclear wavepackets in H 2 and D 2 molecules by measuring the relative phase of high harmonics generated in each molecule by using a novel method with a mixed gas of H 2 and D 2 . We find that not only the single molecule responses but also the propagation effects of harmonics differ between the two isotopes and we conclude that in order to discuss the dynamics of molecules in the single molecule responses, the propagation effects need to be excluded from the raw harmonic signals. The measured relative phase as well as the intensity ratio are found to be monotonic functions of the harmonic order and are successfully reproduced by applying Feynman's path integral method fully to the dynamics of the nuclei and electrons in the molecules.