Interference Fringes Types

The different types of fringes discussed in systems employing division of amplitude. In these systems, interference takes place between the beams reflected from the boundary surfaces of a medium. The general relation used in these cases is given by

2 t cos θ = nλ

This relation refers to either a bright or dark fringe depending on the phase changes, that occur at the various surfaces. In any fringe system, a fringe is a locus of points corresponding to a constant phase difference or a constant path difference. The type of fringes depends on the variation in the values of λ, , t and θ.

1. When θ varies λ, and t are constant.

When a monochromatic beam of light (λ and constant) is incident on a film of constant thickness (t constant), the path difference depends on the value of θ. In this case the fringes obtained are of equal inclination such as the circular fringes obtained in a Michelson interferometer, Fabry Perot interferometer and Lummer Gehrcke plate.

Also, with large value of t, even for a slightly different wavelength there is an appreciable difference in the value of θ. Such fringes are useful in high resolution spectroscopic work.

2. When λ, vary and t, θ constant

If a polychromatic beam of light is incident on a film of constant thickness, the phase of difference depends on λ. On this basis the interference filters are constructed for large values of t. The maxima occur for very nearby wavelengths. For small values of t the maxima occur for widely separated wavelengths.

3. When t varies, λ, and θ are constant

When a monochromatic beam of light (λ, constant) is incident in a film whose thickness varies from point to point, the path difference depends on the thickness of the film at that point. In this case, fringes of equal thickness are obtained. The fringes obtained, with a wedge shaped film as in the case of Michelson’s interferometer with inclined plates, the Newton’s rings formed with a convex surface on a plane glass plate are of this type.

4. When t, λ, vary and θ constant

When polychromatic (say white) beam of light is incident on a film whose thickness varies from point to point, for any particular fringe, the order n is constant. Therefore t/λ is constant. This refers to fringes of the same chromatic order and coloured fringes are obtained. These fringes are useful in the standardization of metre with a Michelson interferometer. Here, white light fringes are used for the determination of zero path difference.

Services: - Interference Fringes Types Homework | Interference Fringes Types Homework Help | Interference Fringes Types Homework Help Services | Live Interference Fringes Types Homework Help | Interference Fringes Types Homework Tutors | Online Interference Fringes Types Homework Help | Interference Fringes Types Tutors | Online Interference Fringes Types Tutors | Interference Fringes Types Homework Services | Interference Fringes Types