How the Detector Operates
Refractive index
When a beam of light passes from one medium into another, the wave velocity and direction changes. The change in direction is called refraction. The relationship between the angle of incidence and the angle of refraction is expressed in Snell's Law of refraction.
Where:
n = Refractive index of medium 1 relative to medium 2
n₂ = Refractive index of medium 2
n1 = Refractive index of medium 1
α 1 = angle of incident light in medium 1
α ₂ = angle of refraction in medium 2
According to the formula below small angles of external deflection are proportional to the difference between the refractive indices of medium 1 and medium 2.
Where:
γ = angle of external deflection
n₂ = Refractive index of medium 2
n1 = Refractive index of medium 1
Factors that Affect Refractive Index
The refractive index of a medium is affected by a number of factors;
Wavelength
The refractive index varies with changes in the wavelength of the incident light beam.
Density
As the density of the medium changes the refractive index changes. At a fixed wavelength of incident light the changes in refractive index are generally linear in relation to the changes in medium density.
The density of a medium will be affected by the following factors:
Composition (if not a pure substance)
Temperature
Pressure
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