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The optical path difference between the paths taken by two identical waves can then be used to find the phase change. Finally, using the phase change, the interference between the two waves can be calculated. Fermat's principle states that the path light takes between two points is the path that has the minimum optical path length.
This formula was first obtained by B.A. Vvedenskij. [3] Note that the power decreases with as the inverse fourth power of the distance in the far field, which is explained by the destructive combination of the direct and reflected paths, which are roughly of the same in magnitude and are 180 degrees different in phase.
The path integral formulation is a description in quantum mechanics that generalizes the stationary action principle of classical mechanics.It replaces the classical notion of a single, unique classical trajectory for a system with a sum, or functional integral, over an infinity of quantum-mechanically possible trajectories to compute a quantum amplitude.
This equation is invalid, however, if the light source's path in space does not follow that of the light signals, for example in the standard rotating platform case (FOG) but with a non-circular light path. In this case the phase difference formula necessarily involves the area enclosed by the light path due to Stokes' theorem. [34]
This path difference is (+) (′). The two separate waves will arrive at a point (infinitely far from these lattice planes) with the same phase , and hence undergo constructive interference , if and only if this path difference is equal to any integer value of the wavelength , i.e. n λ = ( A B + B C ) − ( A C ′ ) {\displaystyle n\lambda ...
If the source has a Gaussian spectrum with FWHM spectral width , then a path offset of will reduce the fringe visibility to 50%. It is important to note that this is a roundtrip coherence length — this definition is applied in applications like OCT where the light traverses the measured displacement twice (as in a Michelson interferometer ).
In this case, the Berry phase corresponding to any given path on the unit sphere in magnetic-field space is just half the solid angle subtended by the path. The integral of the Berry curvature over the whole sphere is therefore exactly 2 π {\displaystyle 2\pi } , so that the Chern number is unity, consistent with the Chern theorem.
For any complex number written in polar form (such as r e iθ), the phase factor is the complex exponential (e iθ), where the variable θ is the phase of a wave or other periodic function. The phase factor is a unit complex number, i.e. a complex number of absolute value 1. It is commonly used in quantum mechanics and optics.