Creation of population gratings in a gas of hydrogen atoms using ultraviolet attosecond pulses

We study the possibility of creating gratings of populations in a gas of hydrogen atoms using a pair of UV attosecond pulses that do not overlap in the medium. In this case, the central frequency of the pulses can either coincide with the frequency of the 1–2 resonant transition from the ground state to the first excited state (the main line of the Lyman series), or be detuned from it. The values of numerically calculated quantities agree with those obtained analytically from the solution of an approximate Schrödinger equation in perturbation theory. We show that, upon resonant excitation, the greatest creation efficiency of gratings is achieved with increasing pulse duration. In the case of nonresonant excitation, on the contrary, the system is excited more efficiently by short quasi-unipolar subcycle pulses than by bipolar multicycle once. The obtained results can be applied to coherent excitation of a single atom (thin layer) using a pair of UV pulses. We show that the modulation depth of gratings can be controlled by changing the carrier envelope phase (CEP) of UV attosecond pulses.