CD Diffraction

Purpose: We are going to distance between the grooves on the CD.

We point a laser beam on a CD, and we put white boards as screen between laser beam and CD without blocking the beam. We have the diffraction pattern on the white boards.



We measure the distance between center to first order maxima distance.

The left first order maxima distance x(left) = 13.1 ± 0.05 cm.
The right first order maxima distance x(right) = 13.3 ± 0.05 cm.

We also measure the distance between the CD and white boards L = 17.2 ± 0.05 cm.

We have the wavelength of laser λ is 670 ± 20 nm = 670 x 10^-9 ± 20 x 10^-9 m.

We use the equation d = mλ/sinθ. For the first maximum order at x, m = 1, d = λ/sinθ.

The distance between the groove in CD due according to the left first order maxima = 1.106 x 10^-6 + 4.7294 x 10^-9 - 3.7551 x 10^-8 m.
The distance between the groove in CD due according to the right first order maxima = 1.096 x 10^-6 + 3.7425 x 10^-8 - 3.7106 x 10^-8 m.

We have the minimum and maximum range of distance d = 1.059 x 10^-6 and 1.111 x 10^-6.

The expected value of distance between of grooves in CD = 1600 nm = 1.6 x 10^-6 m.

We find the expected value of distance between of grooves in CD is out of the range of the calculated distance.

We successfully find distance between the grooves on the CD. However, we find the expected value of distance between of grooves in CD is out of the range of the calculated distance. There are some errors for the data we collected in the experiment. 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. We also do not hold the screen stably by hand so sometimes we shock, which changes the measured distance between the CD and screen L while moving the position of screen and makes the calculated distance x not accurate.