Phase change on reflection

  • #1

Main Question or Discussion Point

We know that reflected light undergo a phase shift of π in EXTERNAL REFLECTION but there is no phase shift in INTERNAL REFLECTION . Does this violate Stokes Relation, which states that every reflected beam undergo of phase shift of π ?
 

Answers and Replies

  • #2
sophiecentaur
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Hi and welcome to PF.
I found this YouTube video which you may find satisfactory. What do you think?
 
  • #4
sophiecentaur
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This video is useful in understanding of Stokes Relations but not where they are used
Yes. It's not in depth but I can't see that Stokes actually contradicts the result of continuity of fields across the boundary.
 
  • #5
Yes. It's not in depth but I can't see that Stokes actually contradicts the result of continuity of fields across the boundary.
True. But it clashes with what I have studied in Interference in Dielectric Films :

(1.) Phase changes by π in external reflection (i.e. reflection in rarer medium when the reflected ray bounces off the boundary of a denser medium).

(2.) Phase changes by 0 (i.e. NO PHASE CHANGE) in internal reflection (i.e. reflection in denser medium when the reflected ray bounces off the boundary of a rarer medium).

(3.) No phase change in any of refraction.

According to Stokes Relation, point (2.) should be false but according to Interference in Dielectric Films, it should be correct.

[emoji54]
 
  • #6
sophiecentaur
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The phases involved are the result of the change in refractive index in the two directions.
True. But it clashes with what I have studied in Interference in Dielectric Films :

(1.) Phase changes by π in external reflection (i.e. reflection in rarer medium when the reflected ray bounces off the boundary of a denser medium).

(2.) Phase changes by 0 (i.e. NO PHASE CHANGE) in internal reflection (i.e. reflection in denser medium when the reflected ray bounces off the boundary of a rarer medium).

(3.) No phase change in any of refraction.

According to Stokes Relation, point (2.) should be false but according to Interference in Dielectric Films, it should be correct.

[emoji54]
We can't argue with what you've learned about dielectric films. (I assume you were getting the right story!) so I guess you need to look at what it actually implied by this time reversal notion with rays. Time reversing involves two incident beams, which need to be the same as the emerging beams. Could that be what you are ignoring when you reckon you've found a flaw? My problem is that it all seems OK to me - but that could just be because I haven't thought deeply enough about it. :wink:
 
  • #7
ZapperZ
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True. But it clashes with what I have studied in Interference in Dielectric Films :

(1.) Phase changes by π in external reflection (i.e. reflection in rarer medium when the reflected ray bounces off the boundary of a denser medium).

(2.) Phase changes by 0 (i.e. NO PHASE CHANGE) in internal reflection (i.e. reflection in denser medium when the reflected ray bounces off the boundary of a rarer medium).

(3.) No phase change in any of refraction.

According to Stokes Relation, point (2.) should be false but according to Interference in Dielectric Films, it should be correct.

[emoji54]
You might want to look at this lecture notes:

http://web.mit.edu/6.161/www/Basic_Electromagnetics-FT07.pdf

Zz.
 
  • #9
sophiecentaur
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sorry it is showing error opening in webpage
The first two pdf pages appear blank but I can see stuff further down the document.
 
  • #10
The first two pdf pages appear blank but I can see stuff further down the document.
sorry no downward or sideward scrolling is there. Upward scrolling causes the page to reload
 
  • #11
sophiecentaur
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sorry no downward or sideward scrolling is there. Upward scrolling causes the page to reload
I can read it all, afaics. Try a different browser, perhaps. I used Safari on the latest OS X.
Edit: You mentioned sideways scrolling so you are using a mobile, I guess.
 
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