#11 CD Diffraction

Objective: 

The purpose of this experiment is to measure the length of the gap between the grooves on the CD and DVD.

Procedures:

1.      Arrange the equipment as guided, shoot the laser to the CD/DVD.

2.      Record distance between two diffracted points on the white board behind the laser, make sure the laser is in the middle.

3.      Record wavelength of the laser and the distance from the board to CD/DVD.

Results:

       The wavelength of the laser is from 630 to 680 nm. Formula is given as:

       d*sin(theta)=d*y/L=n*lambda

       For CD:

        The distance from CD to screen is 47.5cm, distance between two point on the board is 49cm.Thus the angle is 26.32 degree.

    L = 47.5cm, theta = 26.32, y = 24.5cm, lambda from 630 to 680 nm.

    Derived value for d is from 1432 to 1545 nm, the proper distance from internet is 1500, which is in the range.

    For DVD:

    L = 20cm

    y = 19 cm
    Angle theta = 43.5
    Lambda unchanged
    d is from 915 to 988 nm. Proper distance is 740, which is not in the range.

       

Discussion:

    The measurement conducts well for CD. The range is mainly due to the uncertainty of the laser wavelength, but the theoretical value falls in the range. The experiment conducts not so well for the DVD, which does not fall in the range. Maybe DVD has different groove structure or different arrangements, which may cause error in this method of measurement.