Blazed Grating

Using a repetivive structure, it can separate a beam into different wavelengths ${\lambda }_m$:

$a(\sin ({\theta }_i)+\sin ({\theta }_r))=m{\lambda }_m$

Where ${\theta }_i$and ${\theta }_r$are the incidence and reflective angle respectively.

The actual reflection is done in the grating facet, incident light makes an angle ${\theta }_i-\beta$ with the facet normal and gets reflected at the same angle, If we change to the surface normal, we get the relation: ${\theta }_i-{\theta }_r=2\beta$