et’s start by recapping Young’s double slit experiment in that experiment.

Light is passed through two slits it defract from the slits and is projected onto a screen where we see a pattern of light and dark fringes form. These forms due to interference of the light from the two different sources. The reason Young’s double slit experiment is important for the day is it’s very, very similar to the diffraction grating.

In the diffraction grating, instead of two slits, we have a series of many, many slits, generally hundreds, or even thousands of slits per millimeter. When we observed the light that passes through the diffraction grating, we observe at a fraction pattern. This diffraction pattern consists of many bright points of light.

We call these bright points of light, the orders of the diffraction pattern. For example, in the center, we have the zero order, the defraction pattern going up through, we have the first order, second order, third order. And so on. The reason for these bright spots is the light coming from the slits is meeting in phase at these points.

And therefore we get constructive interference in the first order. For example, each leg and its neighbor has a path length difference equivalent to lambda. Meaning that the light will meet in phase. One important difference between a diffraction grating and a double slit. Is that a diffraction grating we’ll split the light up into its components spectrum.

For example, white light, as we know is made up of all of the colors of the spectrum, therefore passing white light through the diffraction grating allows us to see all of these different colors. However, there is an exception that in the zeroth order, the light will remain the same as it is when it’s passed through the defraction grating.