CD Diffraction

Diffraction phenomena is the occurance of waves transcending through a obstruction such that it's wavefronts radiate outwardly and in phase.  In these cases, the obstruction allows waves to pass after splitting the wave.  In the case of lightwaves, the gratings in a material obstruction can split the light into its component wavelengths.

In this lab, a monochromatic light will pass through a screen and be incident to the surface of a compact disc.  The compact disc, with 'pits' carved radially throughout, will act as a diffraction grating.  The material is also reflective, so the  reflected light will be both diffracted and reflected back onto the same screen that the incident wave initially passed through.

Since the lightwave to be used is monochromatic, the diffracted light waves that interfere constructively will produce clear maximum points of intensity on the screen.  The degree to which these maximum points are spread from the source point (the screen hole where the light initially passes through) will help us indicate the width of the pits in the compact disc.

*Laboratory Data has been collected from Olaf Vazquez*

[Photos to be added shortly]

L, distance from screen to compact disc: 42.5 cm
d, width of pits, to be calculated below
x, distance from incident light point source (screen hole), 21cm

Relationship: d sin(theta) = m*lambda, where m =1 for the first maximum intensity subsequent to  the zero angle maximum, and lambda, the wavelength of the monochromatic light = 633nm

Using geometry, we can determine the value for sin(theta) as sqrt(x^2+L^2)

Substituting the geometrical expression into the relationship equation we can solve for d:

d = lambda/x * sqrt(x^2+L^2) = 1.5 micrometers