Gratix

Meet Gratix, a diffraction grating who splits light into sharp beams of colour.

A grating has many equally spaced slits or lines. Light through neighbouring slits travels different distances, and where the extra distance is a whole number of wavelengths the waves add up brightly. This happens at angles where d sin θ = mλ.

A grating with 600 lines per millimetre has spacing d = 1 / 600 mm ≈ 1.67 µm. For green laser light of 532 nm, the first-order beam (m = 1) is at sin θ = 0.532 / 1.67 ≈ 0.32, so θ ≈ 18.6°. Red light, with a longer wavelength, bends further.

With thousands of slits, the bright beams become very narrow, much sharper than with two slits. That is why gratings can separate wavelengths that are very close together, which a prism cannot do as well.

Gratings are at the heart of spectrometers, which reveal the elements in stars and the chemicals in a lab sample. The rainbow sheen on a CD comes from its closely spaced tracks, which act as a reflection grating.