CD Diffraction

Introduction:

Diffraction occurs in a multiple-slit experiment.  This experiment will explore the multiple grooves indented into a common compact disk.  The grooves on the disk will act as the multiple-slits in our diffraction experiment.  The spacing between the grooves will be obtained through the diffraction equation:

 and

where lambda is the wavelength of the laser used, m =1, y is the distance between first order maxima, and L is the distance between the screen of the laser diffraction pattern and the CD.


Steps:

First, we measure the wavelength of our laser.  To do this, we used a diffraction grating with 500 slits per millimeter and the equation mentioned above in a our calculations

Calculations for our laser wavelength are given below:

Since red light ranges around 700nm, we accept our calculations within our uncertainties provided.

After obtaining the wavelength parameter, we proceed to our CD diffraction apparatus seen below.

A parallel setup is accomplished by aligning the edges of our disk and cd placeholders along the edge of our table.  Clamps are aligned accordingly.  Diffraction patterns are marked on our paper screen and measured afterwards.

Calculating the distance between adjacent grooves is done in the calculations below

Questions/Conclusions:

The actual distance between the adjacent grooves on our compact disk is given by the manufacturer's standard value of 1.600 microns.  This gives us

The error is fairly large and falls well out of our uncertainty of .137 microns.
The nature of the experiment itself has multiple parameters and precision setups required.  Our results show  the same order of magnitude after uncertainty is taken into account.  So we are satisfied with this.  Another source of error might be the impurities of the compact disks we used.  This might account for a deviation from the manufacturer's standard value.