  We demonstrate the enhancement and optimization of a cold strontium atomic
beam from a two-dimensional magneto-optical trap (2D-MOT) transversely loaded
from a collimated atomic beam by adding a sideband frequency to the cooling
laser. The parameters of the cooling and sideband beams were scanned to achieve
the maximum atomic beam flux and compared with Monte Carlo simulations. We
obtained a 2.3 times larger, and 4 times brighter, atomic flux than a
conventional, single-frequency 2D-MOT, for a given total power of 200 mW. We
show that the sideband-enhanced 2D-MOT can reach the loading rate performances
of space demanding Zeeman slower-based systems, while it can overcome
systematic effects due to thermal beam collisions and hot black-body radiation
shift, making it suitable for both transportable and accurate optical lattice
clocks. Finally we numerically studied the possible extensions of the
sideband-enhanced 2D-MOT to other alkaline-earth species.
