Diffraction in a diffraction grating occurs when a beam of light passes through many closely spaced slits or grooves, causing the light waves to spread out and interfere with each other. Each slit in the grating acts as a secondary source of wavelets, and these wavelets overlap and interfere constructively or destructively depending on their path difference.
Constructive interference (bright fringes) occurs when the path difference between waves from adjacent slits is an integer multiple of the wavelength. This leads to the formation of distinct, sharp maxima at specific angles, called diffraction orders.
The condition for constructive interference is:
d sin θ = nλ
Where:
- d is the distance between adjacent slits (grating spacing),
- θ is the angle of the diffraction maximum,
- n is the order of the maximum (1, 2, 3, …),
- λ is the wavelength of the light.
Different wavelengths diffract at different angles, so a diffraction grating separates white light into its spectral components. This property makes gratings essential in spectrometers and optical instruments for analyzing the spectral composition of light.