#12: CD Diffraction

The purpose of this lab was to determine the distance between data pits on a CD. This was done using the properties of diffraction, or more specifically, diffraction grating. A 630-nm laser source was placed 0.51±0.005m away from a CD so that its laser had a near-normal incidence on the CD. The reflected diffraction pattern appeared on a whiteboard that was placed next to the source. Since the laser had near-normal incidence, even the zero-order maxima appeared on the edge of the whiteboard.
 First set up the experiment with a lhelium neon laser perpendicularly to the surface of the disk. As the laser hit the surface of the CD, the laser beam diffract and split into multiple beams of light. Both the CD and the laser should be adjusted until the the zero order maximum would shown on the board. Then record the the perpendicular distance between the board and the disc and the distance between the maximums. 

Data and Analysis
tan(θ) = x/Ld=mλ/sin(θ)

Conclusion

This experiment let us have a better understanding of laser diffraction and how it can be used to measure defects in CD spacing. However, there are some errors for the data we collected in the experiment. Since we hold the screen between the laser and CD by hand, and we do not hold the screen to be perpendicular to the laser and CD, which makes the measured distance between the CD and screen L and calculated distance x not accurate. With more precise instrumentation would could significantly decrease our percent uncertainty and difference to more accurately the CD's spacing.