Theory of a resonant interaction of a gas of atoms with standing-wave pulses separated in time

A solution is obtained to the problem of a resonant interaction of a gas of atoms with the field of three strong standing-wave pulses separated in time. A calculation is reported of a correction to the power absorbed by the gas, which oscillates near the center of an atomic line as a function of the field frequency with a characteristic scale of the order of the reciprocal of the time delay between the pulses. It is shown that a signal then appears for all rational values of the ratio of the delays between the pulses and it is related to the transfer–along the time axis–of higher spatial harmonics of the polarization of a medium and of the level populations.