Sawtooth profile concentrating energy into chosen diffraction order
A blazed (sawtooth) grating redirects light into a preferred diffraction order by tilting
each groove facet by the blaze angle θ_b. Blaze condition: λ_b = 2d·sin(θ_b) for Littrow
(θ_i=θ_d). Diffraction orders: sin θ_m = sin θ_i + m·λ/d. Efficiency in order m uses
scalar diffraction: η_m ∝ sinc²((φ_b−φ_m)/π) where φ_b is the phase shift from the
facet tilt. The blazed order can concentrate >70% of light, vs ~40% for a ruled grating.