  OSIRIS is a near-infrared integral field spectrograph operating behind the
adaptive optics system at W. M. Keck Observatory. While OSIRIS has been a
scientifically productive instrument to date, its sensitivity has been limited
by a grating efficiency that is less than half of what was expected. The
spatially averaged efficiency of the old grating, weighted by error, is
measured to be 39.5 +/- 0.8 % at {\lambda} = 1.310 {\mu}m, with large field
dependent variation of 11.7 % due to efficiency variation across the grating
surface. Working with a new vendor, we developed a more efficient and uniform
grating with a weighted average efficiency at {\lambda} = 1.310 {\mu}m of 78.0
+/- 1.6 %, with field variation of only 2.2 %. This is close to double the
average efficiency and five times less variation across the field. The new
grating was installed in December 2012, and on- sky OSIRIS throughput shows an
average factor of 1.83 improvement in sensitivity between 1 and 2.4 microns. We
present the development history, testing, and implementation of this new
near-infrared grating for OSIRIS and report the comparison with the
predecessors. The higher sensitivities are already having a large impact on
scientific studies with OSIRIS.
