  We demonstrate theoretically and numerically that laser-driven many-electron
dynamics, as described by bivariational time-dependent coupled-cluster theory,
may be analyzed in terms of stationary-state populations. Projectors
heuristically defined from linear response theory and equation-of-motion
coupled-cluster theory are proposed for the calculation of stationary-state
populations during interaction with laser pulses or other external forces, and
conservation laws of the populations are discussed. Numerical tests of the
proposed projectors, involving both linear and nonlinear optical processes for
the He and Be atoms, and for the LiH, CH$^+$, and LiF molecules, show that the
laser-driven evolution of the stationary-state populations at the
coupled-cluster singles-and-doubles (CCSD) level is very close to that obtained
by full configuration-interaction theory provided all stationary states
actively participating in the dynamics are sufficiently well approximated. When
double-excited states are important for the dynamics, the quality of the CCSD
results deteriorate. Observing that populations computed from the
linear-response projector may show spurious small-amplitude, high-frequency
oscillations, the equation-of-motion projector emerges as the most promising
approach to stationary-state populations.
