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We present a scheme to enhance the atom number in magneto-optical traps of
strontium atoms operating on the 461 nm transition. This scheme consists of
resonantly driving the $^1$S$_0\to^3$P$_1$ intercombination line at 689 nm,
which continuously populates a short-lived reservoir state and, as expected
from a theoretical model, partially shields the atomic cloud from losses
arising in the 461 nm cooling cycle. We show a factor of two enhancement in the
atom number for the bosonic isotopes $^{88}$Sr and $^{84}$Sr, and the fermionic
isotope $^{87}$Sr, in good agreement with our model. Our scheme can be applied
in the majority of strontium experiments without increasing the experimental
complexity of the apparatus, since the employed 689 nm transition is commonly
used for further cooling. Our method should thus be beneficial to a broad range
of quantum science and technology applications exploiting cold strontium atoms,
and could be extended to other atomic species.
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