  We investigate theoretically the transport properties of a mesoscopic system
driven by a sequence of rectangular pulses applied at the contact to the input
(left) lead. The characteristics of the current which would be measured in the
output (right) lead are discussed in relation with the spectral properties of
the sample. The time-dependent currents are calculated via a generalized
non-Markovian master equation scheme. We study the transient response of a
quantum dot and of a narrow quantum wire. We show that the output response
depends not only on the lead-sample coupling and on the length of the pulse but
also on the states that propagate the input signal. We find that by increasing
the bias window the new states available for transport induce additional
structure in the relaxation current due to different dynamical tunneling
processes. The delay of the output signal with respect to the input current in
the case of the narrow quantum wire is associated to the transient time through
the wire.
