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 \pm 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 \pm 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 .