The Diffraction Order subnode is available from the context menu (right-click the 
Grating parent node) or from the 
Physics toolbar, 
Attributes menu. Each 
Diffraction Order subnode can either release transmitted rays, reflected rays, or both transmitted and reflected rays of a specified diffraction order, depending on the option selected from the 
Rays to release list in the parent 
Grating node.
 
    If the Use relative order numbers is not selected in the settings for the parent 
Grating node, then enter a 
Diffraction order m (dimensionless). The default is 
m = 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.
 
    If Use relative order numbers is selected in the settings for the parent 
Grating node, then enter a 
Relative diffraction order Δm (dimensionless). As above, the default is 
Δm = 0 if no other 
Diffraction Order subnode exists; otherwise the default is 1 greater than the highest relative order that is currently present.
 
    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.