  We present a novel time- and phase-resolved, background-free scheme to study
the extreme ultraviolet dipole emission of a bound electronic wavepacket,
without the use of any extreme ultraviolet exciting pulse. Using multiphoton
transitions, we populate a superposition of quantum states which coherently
emit extreme ultraviolet radiation through free induction decay. This emission
is probed and controlled, both in amplitude and phase, by a time-delayed
infrared femtosecond pulse. We directly measure the laser-induced dephasing of
the emission by using a simple heterodyne detection scheme based on two-source
interferometry. This technique provides rich information about the interplay
between the laser field and the Coulombic potential on the excited electron
dynamics. Its background-free nature enables us to use a large range of gas
pressures and to reveal the influence of collisions in the relaxation process.
