  We use an optically dense, anisotropic magneto-optical trap to study
recoil-induced resonances (RIRs) in the transient, high-gain regime. We find
that two distinct mechanisms govern the atomic dynamics: the finite,
frequency-dependent atomic response time, and momentum-space population
redistribution. At low input probe intensities, the residual Doppler width of
the atoms, combined with the finite atomic response time, result in a linear,
transient hysteretic effect that modifies the locations, widths, and magnitudes
of the resulting gain spectra depending on the sign of the scan chirp. When
larger intensities (\textit{i.e.}, greater than a few $\mu$W/cm$^2$) are
incident on the atomic sample for several $\mu$s, hole-burning in the atomic
sample's momentum distribution leads to a coherent population redistribution
that persists for approximately 100 $\mu$s. We propose using RIRs to engineer
the atomic momentum distribution to enhance the nonlinear atom-photon coupling.
We present a numerical model, and compare the calculated and experimental
results to verify our interpretation.
