Untitled Document

Physics Demo Number: 158

Approximate

Run Time: 5 min

Brewster's Angle By Laser Reflection From a Plastic Block

Demo Description

Linear polarization of a reflected beam of light is achieved by bouncing a 5 mW laser beam off of a plastic block.

Scientific Principles

Light reflected off a dielectric surface is partially polarized by the reflection.
At a particular angle of reflection one finds the polarization to be 100%.

Equipment

Plastic block and a plate of polarizing material
5 mW Demonstration Laser

Equipment Location

Kit (158) {Shared with Kit(108)} on [C-4-4]
Laser on [C-2-4]

Instructions

The 5mw HeNe laser is seen shining straight ahead onto the door in the first photo. Use of the round Polaroid filter seen resting on top of the plastic block shows the laser light to be unpolarized.

One now slides the block over to intercept the laser beam on the front face of the block. This results in a reflected beam angling over to the wall behind the table on the right in the photo. The second photo shows this state of affairs, for the laser beam striking the block,

while the third photo shows the beam on the right hand wall.

If the filter is placed in the beam, either before reflection or after reflection, it can be noted that the reflected beam is partially polarized. Adjustment of the reflection angle by rotating the block will lead to nearly total polarization of the reflected beam. The angle for which total polarization occurs is known as Brewster's Angle.