![]() I don't know the angular position of these bright dots, but here is a diagram of what that would look like: That is how they are listed on the laser. For this picture, the diffraction grating is mounted on the camera. Here is a picture looking through a diffraction grating at a dot made by each of these lasers. I now have 3 different wavelengths of lasers - blue, green and red. If you send several wavelengths through at the same time, they will make bright spots at different locations so that you can see what wavelengths are there. Really, the cool part is that this bright spot location depends on the wavelength. The next bright spot will be where the path length is twice the wavelength. Also, this is the angular location of the first bright spot to the side (there will also be a bright spot at θ = 0). So, there will be constructive interference if: And yes, this assumes that the point where the waves interfere is quite far away (so it is safe to assume these two paths are parallel). Using some simple geometry, I can find the path length difference between path 1 and path 2. In this case, I will not show the waves but just the path the light takes going through two slits. If the light from one slit travels one whole wavelength more than the light from the other slit, then they will be back in phase and constructively interfere (make a bright spot). When do you get a spot with constructive interference? It has to do with path length. It turns out that there is a relationship between the spacing of these bright spots, the wavelength of the light and the slit spacing. When these meet, they will cancel like this: If you shake the string to the side, you can try one pulse and the other an "inverse pulse". When waves add together to make a larger amplitude, it is called constructive interference. What if two people are on opposite ends of the rope and send down a pulse at the same time? What happens when these pulses meet? They add together like this: If you move one end up and down really quickly, you can get a pulse wave traveling down the rope. Take some type of rope and stretch it out on the ground. If you have two waves meeting together at the same place and the same time, they add together. Why? First, there is something you need to know about waves. If you pass a wave (like light) through a whole bunch of openings, you can a nice and clear diffraction pattern. ![]() If the size of the opening is comparable to the wavelength of the wave, the bending can be noticeable. What happens when a wave passes through some opening? It diffracts - or you like, you could say "bends".
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