Path difference and phase difference.

In summary: But in general, a ray's position and direction can be unambiguously described by its phase and its wavenumber.
  • #1
Fuego
43
0
Pardon the pun, but what's the difference between path difference and phase difference (when talking about interfering light waves)?
 
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  • #2
Path difference is the distance one wave (from a coherent source) has to travel from its source to the observer. ie one observers ear may receive the crest and the other ear receive the trough. this would give a path difference of 1/2 wavelength.
Phase difference is best understood by considering a cosine wave and a sine wave. they are 90degrees out of 'synch' with each other and would produce destructive interference.
i hope someone with more brains than me can clarify your quandary. I think i am corect but i am sure someone here can be more specific.
 
  • #3
bootsam said:
Path difference is the distance one wave (from a coherent source) has to travel from its source to the observer. ie one observers ear may receive the crest and the other ear receive the trough. this would give a path difference of 1/2 wavelength.
Phase difference is best understood by considering a cosine wave and a sine wave. they are 90degrees out of 'synch' with each other and would produce destructive interference.
i hope someone with more brains than me can clarify your quandary. I think i am corect but i am sure someone here can be more specific.

I believe the equation would be phase difference = 2pi/lambda*path difference
 
  • #4
As a beam traverses space, the phase of a ray goes as [tex]\phi (z) = k n z [/tex], where k is the wavevector, n the refractive index, and z the distance. The quantity nz (or nd, where d is the thickness of an object) is referred to as the optical thickness. It's easy to make the sitation more complicated- make the refractive index vary with location, for example. Or make it vary with wavelength. Then the phase delay *relative to another ray*, which is the important thing, is given by more complex versions of the above formula.

Even so, there is no difference between path and phase difference, when you are able to sensibly speak of rays. This is not always the case- strongly focused light, for example. Simply considering polarization can create difficulties, forcing you to keep track of the propogation axes by hand.
 

What is path difference?

Path difference refers to the difference in distance traveled by two waves from their sources to a particular point. It is measured in terms of wavelength and can result in constructive or destructive interference.

How does path difference affect interference?

Path difference plays a crucial role in determining the type of interference that occurs between two waves. When the path difference is equal to a whole number of wavelengths, it results in constructive interference, while a path difference of half a wavelength causes destructive interference.

What is phase difference?

Phase difference refers to the difference in the starting point of two waves with the same frequency. It is measured in degrees or radians and can also result in constructive or destructive interference.

How is phase difference related to path difference?

Phase difference and path difference are closely related. Path difference is the physical distance traveled by two waves, while phase difference is the difference in the starting point of the waves. They both determine the type of interference that occurs between the waves.

What are some real-life applications of path difference and phase difference?

Path difference and phase difference have various applications in fields such as optics, acoustics, and telecommunications. They are used to study interference patterns, design sound systems, and improve signal transmission in communication devices.

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