Experiment 12: CD diffraction

When you look the DVD into a micro structure level, you can see there are little curb on the surface of the DVD. By using the diffraction method, we can simply measure the distance between the grooves on the DVD.
The one we have was a DVD, and the method we use is to point the laser at a angle to the DVD. A beam of laser will diffraction on the other side of the DVD where we put the white board to measure the distance between the first order maxima

Even thought its hard to see whats happening in the picture, we can see the light been goes into the DVD and another light beam comes out from the DVD.

Since we know the wavelength of the laser beam, which is around 670nm. Also, the distance between the DVD to the white board is around 0.07m. The distance between the center and the first order maxima is around 2.8cm. By using the diffraction formula, we can calculate the estimate groove distance by using y=m λx/a  where y is the distance between the maxims, x is the distance between the source to the screen, λ is the wave length. In this case, m is 1 since we measured the first maxim. The value we try to find is a which is around 1.675*10^-6 m.  As we compare to the manufacturer's standar value 1600nm, our result is very close to the manufacture's number. The difference between the numbers is due to our measurement. Since we just use a regular ruler to measure the distance between the first maxim, there are a larger uncertainties in it. Also, the distance between the board and the source is also measured with the same method, which gave us a larger uncertainties. With all the uncertainties we have, we can conclude that our measurement is very reliable, and it proved that the DVD has grooves about 1.6*10^-6 m  in length