WHAT IS THE FORMULA FOR PHASE DIFFERENCE?

Optical path difference is the phase shift which happens between two previously coherent sources when passed through different mediums. For example a wave passed through glass will appear to travel a greater distance than an identical wave in air. This is because the source in the glass will have experienced a greater number of wavelengths due to the higher refractive index of the glass.

The OPD can be calculated from the following equation:d=n*d

where d₁ and d₂ are the distances of the ray passing through medium 1 or 2, n₁ is greater refractive index (e.g., glass) and n₂ is the smaller refractive index (e.g., air).

formula for path difference is 2pi bi lambda*path difference