The emergent angle of light of a particular wavelength through a diffractive surface.
$$
\theta = \arcsin\left( bm\lambda + \sin\left(\theta_i\right) \right)
$$
Where:
- $\theta$ [°]: Angle of diffracted ray with respect to the optical axis.
- $m$: Diffraction order.
- $\lambda$ [m]: Wavelength.
- $b$ [1/m]: Fringe frequency.
- $\theta_i$ [°]: Incident angle.
Diffraction Gratings Tutorial