Atomic stabilization in superintense high-frequency fields has been studied theoretically for decades and has led to a wealth of profound and intrigue concepts in strong-field physics. It is usually discussed in the Kramers-Henneberger (KH) frame, i.e., the moving coordinate frame of a free electron responding to the laser field. In the KH frame, the ground state wave function of the atom splits into two non-overlapping peaks and the atom becomes stabilized against ionization when the laser frequency is much higher than the bound state frequency of the atom. On the other hand, in an intense low-frequency (e.g., in the infrared regime) laser field the tunneling limit of multiphoton ionization is more appropriately described by the Keldysh theory. In contrast to the high-frequency multiphoton ionization, the low-frequency atomic stabilization in the tunneling regime is a more subtle and unsettled question that needs further experimental and theoretical investigation.

Recently, researchers at Peking University measured the photoelectron angular distributions from single ionization of atoms produced by a linearly polarized infrared laser and observed that the yield of near-zero-momentum electrons is much suppressed in the deep tunneling ionization regime that was called the local ionization suppression phenomenon. They observed that, as the intensity of the field increases, the relative contribution of low energy photoelectrons to the total ionization yield decreases. With a three-dimensional semi-classical electron ensemble model, they have reproduced this pronounced local ionization suppression effect and uncovered the underlying physics as partial atomic stabilization. It was found that, when the electrons tunnel in a certain time window at the rising front of a laser cycle, a fraction of atoms an be finally excited into the Rydberg states with high-lying elliptical orbits. Those stabilized atoms can make up the suppressed yield of the low-energy ionized electrons. This work was published on [Hong Liu, Yunquan Liu, Libin Fu, Guoguo Xin, Difa Ye, Jie Liu, X.T.He, Yudong Yang, Xianrong Liu, Yongkai Deng, Chengyin Wu, Qihuang Gong, Phys. Rev. Lett. 109,093001(2012)].