Diffracted Angle and Littrow Angle of Reflective Gratings
If m is negative, it means that the diffracted light and diffracted light are on the same side of the normal. If m is positive, it means that the diffracted light and diffracted light are on the opposite side of the normal.
$\frac{[ sin(\theta_m) + sin(\theta_i)]}{N}$= $m \lambda$
$\theta$=arcsin$\frac{N m \lambda}{2}$
Raster Line Density $N$; Incidence Angle $\theta_i$; Order $m$; Wavelength $\lambda$
Diffracted Angle $\theta_m$; Littrow Angle $\theta$;