conclusion
a.Place the CD, label-side down, near the center of the workspace.
b.Put a piece of cardboard to the right of the CD, and another piece of cardboard behind the CD. Both pieces should be about the same thickness as the CD. You will be placing the box on top of all this. The cardboard prevents the box from wobbling.
c.If you want, put a piece of paper or tissue over the back half of the CD, to prevent scratching.
d.For measuring the angles, you will attach the protractor to the index card, flush at the bottom. Use a stack of two cardboard spacers at the points indicated, so that the laser pointer can shine down between the index card and the protractor.
e.Tape the index card to the side of the box (we used a wooden box for holding magazines). The index card and protractor should be flush with the bottom of the box.
f.Carefully place the box over the CD and cardboard pieces. You want the index card lined up along the diameter of the CD, parallel to the front of the table. The center of the protractor should be lined up midway between the center and the rim of the CD.
g.A stack of books makes a convenient elbow rest for the person holding the laser pointer. Rest your fingers against the box as shown to help hold the laser pointer steady.
h.Before you turn on the laser pointer, make sure that no one is in the path of the diffracted beams (the plane of the index card, extended out on both sides and above).
i.Direct the laser pointer beam down the face of the index card, and align the beam with the center of the protractor. You may have to fiddle slightly before you see a diffraction pattern like the one in the photo. Make your adjustments carefully, keeping the beam as close to parallel with the card as possible.