Parity effects in Rydberg-state excitation in intense laser fields

Conservation of parity plays a fundamental role in our understanding of various quantum processes. However, it is difficult to observe in atomic and molecular processes induced by a strong laser field due to their multiphoton character and the large number of states involved. Here we report an effect of parity in strong-field Rydberg-state excitation (RSE) by comparing the RSE probabilities of the N 2 molecule and its companion atom Ar, which has a similar ionization potential but opposite parity of its ground state. Experimentally, we observe an oscillatory structure as a function of intensity with a period of about 50 TW / cm 2 in the ratio between the RSE yields of the two species, which can be reproduced by simulations using the time-dependent Schrödinger equation (TDSE). We analyze a quantum-mechanical model, which allows for interference of electrons captured in different spatial regions of the Rydberg-state wave function. In the intensity-dependent RSE yield, it results in peaks with alternating heights with a spacing of 25 TW / cm 2 and at the same intensity for both species. However, due to the opposite parities of their ground states, pronounced RSE peaks in Ar correspond to less pronounced peaks in N 2 and vice versa, which leads to the period of 50 TW / cm 2 in their ratio. Our work reveals a novel parity-related interference effect in the coherent-capture picture of the RSE process in intense laser fields.