Search for the collective tunneling effect under ionization of high multiplicity Li-like ions by two laser beams of extreme intensity.

The estimates of the probability of simultaneous tunneling of two electrons from multiply charged Li-like ions in high-intensity laser field are given. It is shown that for the atoms with the nuclear charge Z_m ≫ 1 the probability per unit time of collective tunneling of a pair of electrons 2s – 1s can exceed the probability of detachment of the 1s electron by more than an order of magnitude. It creates favorable conditions for searching for the collective tunneling effect under the ionization of heavy, multiply charged ions. The relative contributions of the sequential and collective ionization channels can be separated with the use of a two-beam experimental setup. Taking into account that in order to observe the effect the intensities exceeding 10²¹ W/cm² in one of the beams are required, the proposed experimental scheme needs the use of laser pulses of extreme power, that is planned to be obtained, in particular, at the XCELS facility.