Modelled 2nd-order absolute grating efficiency for the COSIE blazed reflection grating. We calculated efficiencies assuming two coating configurations: 78 Å of Zr with a 10 Å oxidation layer (black), and 88 Å of Zr capped by 201 Å of Al and a 40 Å oxidation layer (red). We also considered two polarization states of the incident beam: transverse electric (TE, solid) and transverse magnetic (TM, dot-dash).