Add the Diffraction Order subnode to the 
Grating feature. Each 
Diffraction Order subnode can either release transmitted rays, reflected rays, or both transmitted and reflected rays of the specified order, depending on the option selected from the 
Rays to release list in the parent 
Grating node.
 
    Enter a Diffraction order m (dimensionless). The default is 
0 for the first 
Diffraction Order added. When more diffraction orders are added to the model, the new default is the highest diffraction order currently present, plus 
1.
 
    When the ray intensity or power is solved for, enter the Reflectance R and the 
Transmittance T (both dimensionless). If the reflectance or transmittance of a certain diffraction order is exactly zero, that diffraction order will not be released.