A grating is an arrangement consisting of a large number of parallel slits of same width and separated by equal opaque spaces. (a+b) is called grating element or grating constant. It can be seen that distance between two consecutive slits is grating element.

James Gregory (1638–1675) observed the diffraction patterns caused by a bird feather, which was effectively the first diffraction grating to be discovered. Thomas Young performed a celebrated experiment in 1803 demonstrating interference from two closely spaced slits.

The farther away from the screen (larger L), the wider the pattern of light becomes. The narrower the opening (smaller a), the wider the pattern of light becomes!

β=ϕ2=πasinθλ we obtain. E=NΔE0sinββ Equation 4.3.10 relates the amplitude of the resultant field at any point in the diffraction pattern to the amplitude NΔE0 at the central maximum. The intensity is proportional to the square of the amplitude, so.

We say that an order of diffraction is missing if it disappears as a consequence of the overlapping of the interference and the diffraction patterns. The sinc has several zeros (when sin(x)=0 except from x=0), and if one of these zeros overlaps a maximum of interference, we see nothing. So, there is missing order.

The minima are given by Equation 4.1, a sin θ = m λ a sin θ = m λ . The first two minima are for m = 1 and. m = 2 . Equation 4.4 and Equation 4.2 can be used to determine the intensity once the angle has been worked out.

When the widths of the slits are narrow, light undergoes diffraction and the light waves overlap on the screen. Hence, the intensity of the light is more as the width of the slit increases.

The amount of diffraction depends on the wavelength of light, with shorter wavelengths being diffracted at a greater angle than longer ones (in effect, blue and violet light are diffracted at a higher angle than is red light).