CD diffraction

In this lab we measured the width of the grooves in a CD by using the principles we know about laser diffraction

The distance between these groves is far too small for a the human eye to measure. With diffraction however, we can measure the distance between observed maxima on the diffraction pattern resulting from a laser (λ = 670 nm) reflected off of a CD. The grooves in a cd act as a reflection diffraction grating, so the distance from the center to the m'th maximum can be found as sin(θ) = mλ/d where d is the groove spacing.

Our data was as follows:

After plugging in all the numbers, we got an average d of 2.7*10^-5 meters
We had a very large error which probably due to the fact that our laser might not have been perfectly incident on the diffraction grating (ie, flat spot on the cd), and we are getting thin film interference from the plastic disk.