# Can someone explain optical path difference?

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#1
Ok so the definition seems to be is the distance a wave would travel in air in the same time as it travelled in another medium.

But I don't understand why the formula is then opd=refractive index*geometrical path difference ??
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3 years ago
#2
(Original post by Mystery.)
Ok so the definition seems to be is the distance a wave would travel in air in the same time as it travelled in another medium.

But I don't understand why the formula is then opd=refractive index*geometrical path difference ??
Refractive index

Where c is the speed of light in a vacuum and v is the velocity through the medium.

Optical path length is defined as the product of the refractive index and the geometrical distance the light travels.

Optical path difference is a way of describing the phase shift between two paths emanating from the same coherent light source arriving at the same point after propagating different lengths and/or different mediums.

If the same medium is propagated in both cases then the refractive index is common and can be taken outside brackets:

then

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#3
(Original post by uberteknik)
Refractive index

Where c is the speed of light in a vacuum and v is the velocity through the medium.

Optical path length is defined as the product of the refractive index and the geometrical distance the light travels.

Optical path difference is a way of describing the phase shift between two paths emanating from the same coherent light source arriving at the same point after propagating different lengths and/or different mediums.

If the same medium is propagated in both cases then the refractive index is common and can be taken outside brackets:

then

Ok that clears it up a bit, thank you.
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