  We generate 555.8nm light with sub-MHz linewidth through the use of laser
injection-locking of a semiconductor diode at 1111.6nm, followed by frequency
doubling in a resonant cavity. The integrity of the injection lock is
investigated by studying an offset-beat signal between slave and master lasers,
by performing spectroscopy on the $(6s)^{2}$ $^{1}S_{0}-\,(6s6p)$ $^{3}P_{1}$
transition in magneto-optically trapped ytterbium, and by demonstrating
additional laser cooling of $^{171}$Yb with the 555.8nm light. For the
$^{1}S_{0}-$ $^{3}P_{1}$ spectroscopy, we confirm the linear dependence between
ground state linewidth and the intensity of an off-resonant laser, namely, that
used to cool Yb atoms in a $^{1}S_{0}-$ $^{1}P_{1}$ magneto-optical trap. Our
results demonstrate the suitability of injection locked 1100-1130nm laser
diodes as a source for sub-MHz linewidth radiation in the yellow-green
spectrum.
