Experiment 12: CD Diffraction

Introduction: The purpose of this procedure is to measure the distance between the burned in grooves of a CD using a laser by analyzing its diffraction pattern.

Procedure: We first found the wavelength (lambda) for the laser. We did this by shining a laser through a diffraction grating at a wall. We measured the distance from the grating to the wall (L) and found the distance between the slits on the grating (d) by dividing .001 meters by 600, because that was the number of lines per millimeter. We also determined theta by measuring the distance between the primary laser spot and the brightest maxima (y) and using some trig identities.

We then cut a hole in a piece of paper and held it upright over the table parallel to a CD.

We measured the distance between the CD and the paper and directed the laser through the hole onto the CD. We then measured the distance between the middle and one of the outer laser dots.

Data and Analysis: 

This is the calculation for theta from the first picture with uncertainty.

This is the calculation for the wavelength of the laser with uncertainty. The value printed on the laser was 650 nm so our result is confirmed.

This is the calculation for the distance between the groves in  the CD (d).

This is the percentage error of the industry standard of the distance between the groves (1600 nm) and the experimental value.

We found uncertainty for all values by finding the maximum and minimum values of the required variable which were as a result of uncertainty in measurement. We then average the max and min and subtracted the average from the max, and the min from the average. For d, the value was found to be 1573.5 nm ± 189.5 nm. The industry standard is within this uncertainty value so our results are confirmed.