The possibility of modulation of an Autler-Townes doublet structure in an atomic continuum by changing the phase difference between two incident femtosecond laser pulses is investigated theoretically. Numerical simulations are carried out by solving the three-dimensional time-dependent Schrödinger equation for a Na atom interacting with a two-color field, a fundamental, and its second harmonic. It is found that a sinusoidal modulation of the individual members of the doublet, as a function of the phase difference, can be achieved at low intensities of the order of ${10}^{10}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2.$ Such modulations of the sharply defined electron currents (where the width is of the order of the fine structure of the Autler-Townes levels) may be detected by high-resolution photoelectron spectroscopy. It is also shown that at a higher intensity of the order of ${10}^{12}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2$ the amplitude of modulation diminishes, indicating that lower intensities are to be preferred for the present purpose.

• Received 18 September 1997

DOI:https://doi.org/10.1103/PhysRevA.57.R3176