Preparing for Lower Sixth Physics #17: Diffraction Grating

I have previously posted about the way that laser light spreads out when it goes through the narrow gap between two laser blades. It is also possible to do that by painting glass black and using the razor blade to scratch a narrow line on instead. A diffraction grating is glass painted black that has had an awful lots of narrow lines carved into it. In the picture above, the 2 clear rectangles are bits of black painted glass with so many parallel lines carved into them that it now looks clear. The one on the right has 600 lines carved into 1 mm. Think about it!

Now look at the pattern you get when you shine a laser beam through the grating. The dots are symmetrically placed about the centre but become increasingly dim as you move away from the centre. The formula to describe this will be part of the course.