diffractiongrating

A diffraction grating is an optical component consisting of many closely spaced parallel grooves or slits. When light is incident on the grating, each groove acts as a source of diffracted waves, and the waves from different grooves interfere to produce constructive maxima at specific angles that depend on wavelength.

Gratings are typically made as transmission gratings (light passes through a transparent substrate) or reflection gratings (light reflects from a grooved surface). They can be ruled, where grooves are mechanically engraved; or holographic, where interference patterns are recorded electro-optically. Blazed gratings have a sawtooth groove profile to favor a chosen diffraction order.

The grating equation is d sin(theta_m) = m lambda, with d the groove spacing, m the diffraction order, lambda the wavelength, and theta_m the angle of the m-th order maximum relative to the normal. Increasing m or decreasing d increases angular dispersion; higher groove density provides greater spectral separation.

Performance is commonly described by the resolving power R = lambda/delta_lambda = mN, where N is the number of illuminated grooves. Efficiency depends on groove shape, blaze angle, polarization, and wavelength. There is a trade-off between resolution, efficiency, and spectral range.

Applications include optical spectroscopy and spectrographs, where gratings separate light into spectra, laser line selection, and various consumer technologies (compact discs, DVDs).

Manufacture involves ruled techniques or holographic methods; grating properties are chosen to optimize resolution and efficiency for a target wavelength range. Gratings have been central to spectroscopy since the 19th century and remain widely used in research and industry.