Polarized light are those that are vibrating in one direction- in a single plane such as up and down. Those that are vibrating in more than one direction — in more than one plane such as both up/down and left/right — are called unpolarized light. Generally, unpolarized light can be considered to be vibrating in a vertical and a horizontal plane. To polarize light, one can transmit the light through a polariod filter which will only allow light of single polarity to pass. The resulting light will be polarized light of half intensity.
If two polaroid filters are used and placed so that one is rotated 90 degrees to the other, no light will be able to pass. Some polarization will also occur during reflection, refraction, and scattering of light. When reflecting off non-metallic surfaces, the resulting light will be polarized parallel to the reflected surface. During refraction, a beam of light will be split up into two polarized beams, one polarized parallel and one perpendicular to the boundary. Scattering also causes partial polarization. Characteristics of Polarization
Polarization is a phenomenon peculiar to transverse waves, i. e. , waves that vibrate in a direction perpendicular to their direction of propagation. Light is a transverse electromagnetic wave (seeelectromagnetic radiation ). Thus a light wave traveling forward can vibrate up and down (in the vertical plane), from side to side (in the horizontal plane), or in an intermediate direction. Ordinarily a ray of light consists of a mixture of waves vibrating in all the directions perpendicular to its line of propagation.
If for some reason the vibration remains constant in direction, the light is said to be polarized. It is found, for example, that reflected light is always polarized to some extent. Light can also be polarized by double refraction . Any transparent substance has the property of refracting or bending a ray of light that enters it from outside. Certain crystals, however, such as calcite (Iceland spar), have the property of refracting unpolarized incident light in two different directions, thus splitting an incident ray into two rays.
It is found that the two refracted rays (the ordinary ray and the extraordinary ray) are both polarized and that their directions of polarization are perpendicular to each other. This occurs because the speed of the light in the crystal—hence the angle at which the light is refracted—varies with the direction of polarization. Unpolarized incident light can be regarded as a mixture of two different polarization states separated into two components by the crystal. (In most substances the speed of light is the same for all directions of polarization, and no separation occurs. In actual situations where we want to polarize light, we often want some of the normal light to get through too, so we can see the object we’re looking at. This is achieved by making slits, which are actually long narrow scratches, on a piece of glass. The scratches must be very narrow and close together, because individual light waves are tiny. A bit of normal light can still get through the glass between the scratches, but most of the light is forced to try to vibrate through them … and only the light vibrating along the length of a ‘scratch’ can get through. | In the picture of the polarizing sunglasses at the left, you can see an expanded view of one of the lenses. Although not drawn to scale (you need a microscope to see the scratches), this will give you an idea of how they work. Only light vibrating up and down can easily get through the scratches. Light vibrating in other directions has a hard time getting through. In particular, horizontally vibrating waves will be stopped completely. Since they are the cause of glare, polarizing sunglasses will stop the glare waves, and the truck will look like this:|