  We present an experimental and theoretical study of carrier-envelope phase
(CEP) effects on the population transfer between two bound atomic states
interacting with pulses consisting of many cycles. Using intense
radio-frequency pulse with Rabi frequency of the order of the atomic transition
frequency, we investigated the influence of CEP on the control of phase
dependent multi-photon transitions between the Zeeman sub-levels of the ground
state of $^{87}$Rb. Our scheme has no limitation on the duration of the pulses.
Extending the CEP control to longer pulses creates interesting possibilities to
generate pulses with accuracy that is better then the period of optical
oscillations.
