Huygens' principle and interference

Grating $d=1.67\times10^{-6}\,\text{m}$ (600 lines/mm), $\lambda=500\,\text{nm}$: $\sin\theta = (1\times500\times10^{-9})/(1.67\times10^{-6}) = 0.299$, $\theta \approx 17.4^\circ$ for $m=1$.

Spectrometers, monochromators, wavelength measurement

Far-field (Fraunhofer) diffraction