The ratio between the speed of light in medium to speed in a vacuum is the refractive index. When light travels in a medium other than the vacuum, the atoms of that medium continually absorb and re-emit the particles of light, slowing down the speed light. In this article, let us discuss the refractive index of water and various mediums.

Where,

• n is the refractive index
• c is the velocity of light in a vacuum ( 3 × 10⁸ m/s)
• v is the velocity of light in a substance

The vacuum has a refractive index of 1. The refractive index of other materials can be calculated from the above equation. Higher the refractive index, the higher the optical density and slower is the speed of light. The table below lists the refractive index of different media.

Material

Refractive Index

Air1.0003

Water

1.333

Diamond2.417

Ice1.3

Ethyl Alcohol

1.36

The refractive index of glass ng is 1.52 and refractive index of water nw is 1.33. Since the refractive index of glass is higher than the water, the speed of light in water is faster than the speed of light through glass. If the refractive index of a medium is greater than that of another, then the first medium is said to be optically denser. Most of the substances we know have a positive refractive index having value more than zero. The material will have a negative refractive index when it has negative permittivity and permeability.

The refractive index provides a measure of the relative speed of light in different media. Knowing the refractive indices of different media helps the student to identify the direction in which way the light would bend while passing from one medium to another.

Why is high refractive index important for optical polymers?

Optical polymers with high refractive index allow light rays to bend more within the material, which helps in lowering the profile of the lens. Also, as the refractive index increases, the thickness of the lens decreases, resulting in less weight.

What is refractive index gradient?

• The refractive index gradient is defined as the rate of change of refractive index with respect to distance in the material. Distance refers to the slope of the refractive index profile at any point.
• The refractive index gradient is expressed in terms of reciprocal of a unit of distance.
• An example of a refractive index gradient is the rate of change of refractive index at any point with respect to distance.
• The refractive index gradient is a vector point function.