  Motivated by recent experimental findings for an organic superconductor,
charge oscillations that emerge after a strong pulse of an oscillating electric
field is applied are studied in electron systems in a superconducting phase on
a lattice with a dimerized structure. They are analyzed using Fourier spectra
of charge densities whose time profiles are obtained by numerically solving the
time-dependent Schr\"odinger equation within a mean-field approximation.
Depending on the strengths of attractive interactions, different
charge-oscillation modes appear. For weak attractions, the charge-oscillation
mode is an electronic breathing mode, which was previously found for repulsive
interactions. For strong attractions, it is a pair analog of the electronic
breathing mode (a `pair' breathing mode). For intermediate attractions, it is
another mode whose transient current distributions are considerably different
from those of the breathing modes. We investigate how their frequencies and
amplitudes depend on interactions and transfer integrals.
