ine spacing is going to be one of the fundamental parameters that we need in our calculation. Now, what we actually need is the distance. Between two slits, but what, again, you usually get when you buy a diffraction, grading are the number of lines. And in this case lines and slits basically mean the same thing.

So you can also call this just the distance between lines. You again, would have something like lines per millimeter. So one example of diffraction grating that we just have sitting around has 600 lines per mm.

all we have to do is take our line number density and take the inverse.

And you see that that’s going to give you when you flip these units upside down the right thing and this actually works out to be one in two thirds, micron between the lines.

Notice here that the spacing we’re talking about is much, much smaller than the spacings we were talking about for double slit interference.

Typically diffraction gradings are going to be when we have really, really small length skew interestingly, you can see this phenomena in the world, around you on some like skew that are.

So for reflection gradings, we’re not actually going to do a full mathematical analysis is much easier to do the mathematical analysis for the for the transmission gradings , in the end really works the same way, but instead of thinking about spaces that you can or can’t pass through that it would actually be these little mirrors that are at an angle.

So reflection gradings are actually easier to see in the world around us. One example. Are iridescent structures that in this case, this is a peacock feather butterfly wings we’ll have this as well.

And this really is not nature intending to form a diffraction grading, but once you have cellular structures that are reflective in any way, And you have them lined up. You see that there are these very regular repeating grooves, and that is enough to get a diffraction grading. Now we’re not about to do spectroscopy off a peacock feather.

And if you zoom. The surface of a CD and DVD is made up of a bunch of little pits that were reflect light in different ways. And so once you have those pits that are actually organized in a repeating structure, that is enough to get these pattern. Effectively the DVD or CD is serving as a diffraction grating