  We demonstrate backward-directed continuous-wave (cw) emission at 2.21 {\mu}m
generated on the 4P3/2-4S1/2 population-inverted transition in Na vapors
two-photon excited with resonant laser light at 589 and 569 nm. Our study of
power and atom-number-density threshold characteristics shows that lasing
occurs at sub-10 mW total power of the applied laser light. The observed 6 mrad
divergence is defined mainly by the aspect ratio of the gain region. We find
that mirrorless lasing at 2.21 {\mu}m is magnetic field and polarization
dependent that may be useful for remote magnetometry. The presented results
could help determine the requirements for obtaining directional return from
sodium atoms in the mesosphere
