Optics ** 6H20.10 ** Polarization

Polarization by reflection

Brewster's angle

WARNING: Please be careful with the laser. Always close the shutter when not in use.


Theory: When a beam of unpolarized light reflects from a surface at the Brewster angle, the reflected beam will be polarized along a direction parallel to the surface. The Brewster angle is the angle of incidence that results in a 90 angle between the reflected and refracted beams.

Description: First prepare the water tank by mixing in a small amount of milk powder. This scatters the laser beam, making the refracted beam visible. Next, arrange the laser beam so it strikes the water surface at the Brewster angle. For an air-water interface, the Brewster angle is about 53. You should see a 90 angle between the reflected and refracted beams - turn out the lights and use chalk dust to make the incident and reflected beams visible.

If a polarizer is placed in the path of the reflected beam the beam is completely blocked when the polarizer is aligned with it's transmission axis perpendicular to the water surface. When the incident angle is not the Brewster angle the beam is not completely linearly polarized, so some light will always get through the polarizer.

Setup time: 30 minutes

References: (available in the demo room)