  We investigate photo assisted electronic transport in a
normal-metal/BCS-superconductor junction with a microscopic Hamiltonian
approach, for several types of periodic voltage drives applied on the
normal-metal side. The time-dependent current and the photo-assisted noise are
computed to all orders of the tunneling Hamiltonian using a
Keldysh-Nambu-Floquet approach. An excess noise analysis allows one to
determine to what extent pure electronic excitations with a small number of
electrons per period can be generated by the different drives. When the
superconducting gap is small compared to the drive frequency, the junction
behaves like a normal-metal junction and minimal excess noise is reached for
Lorentzian voltage drives carrying an integer charge (levitons). In the
opposite regime of a large-gap, the excess noise vanishes for half-quantized
levitons, giving rise to the perfect transmission of a Cooper pair on the
superconducting side. This microscopic approach also allows us to address the
intermediate regime, when the drive frequency is comparable to the gap,
allowing us to study the non-trivial interplay between Andreev reflection and
quasiparticle-transfer processes. Our analysis also shows the appearance of
Tien-Gordon-type relations connecting the current and noise in the AC-driven
junction to their DC counterpart, which we investigate in details. Finally, the
possibility to build a reliable on-demand source of Cooper pairs with this
setup is examined using realistic experimental parameters.
