Polaroid

Most waves aren’t exactly very big, so we can’t just cut a slot into a piece of cardboard or something and expect it to work as a polariser. Instead, we use a special material called polaroid.

It’s made up of long-chain molecules that are all aligned in the same direction. When an unpolarised wave passes through the polaroid, only the component of the wave that is oscillating in the same direction as the molecules is allowed to pass through - the rest is absorbed by the material.

For example, if the polaroid is aligned vertically, only the vertical component of the wave will pass through, while the horizontal component will be absorbed.

This essentially creates a ‘slot’ for the wave to pass through, just on a much smaller scale.