Why Can't We See Diffraction from Metal Surfaces?

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Discussion Overview

The discussion revolves around the phenomenon of diffraction from metal surfaces, exploring why diffraction patterns are not typically observed in metals compared to other materials like dielectrics. The scope includes theoretical explanations, properties of electromagnetic waves, and the role of free electrons in metals.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the atomic arrangement in metals acts like a 3-D grating, yet smooth metal surfaces primarily reflect light, leading to questions about the visibility of diffraction.
  • Others argue that the presence of a sea of free electrons in metals affects the refractive index, which is complex, with the imaginary part contributing to absorption and reflection of electromagnetic waves, thereby preventing the wave from interacting with the atomic grating.
  • A participant questions why diffraction patterns are not seen in dielectrics, suggesting that the distance between atoms in crystals is too small compared to the wavelength of visible light, which may limit diffraction.
  • It is noted that X-rays and gamma rays can diffract through crystals and metals, as these high-energy waves can penetrate the surface and interact with the atomic structure.
  • One participant acknowledges a mistake regarding the role of the real part of the refractive index in reflection, indicating ongoing refinement of understanding.
  • Another participant seeks clarification on the relationship between the imaginary part of the refractive index and the absorption of electromagnetic waves in metals.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms behind diffraction in metals versus dielectrics, with no consensus reached on the primary reasons for the lack of observable diffraction patterns in metals.

Contextual Notes

Some limitations include the dependence on definitions of refractive index, the complexity of electromagnetic wave interactions with materials, and the unresolved nature of how these factors influence diffraction visibility.

brianeyes88677
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The atoms in a metal (ex. Cu) are arranged as a 3-D grating. But to our common sense ,smooth metal surfaces only reflect lights. Why can't we see diffraction from metal surfaces?
 
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The metals contain a see of free electrons. In EM we know refractive index for metals is complex. Imaginary part of n is responsible for absorption and reflection of EM waves. This sea is like a cover which is in surface of metals. Therefore the wave cannot see grating.

Why can't we see diffraction pattern from crystals without see of free electrons like dielectrics?

Since from formula of diffraction sin(Teta)=i*landa/d must d>landa( <=> sin(Teta)<1) and in crystal the d(distance between two atoms) is about angstrom therefore there is no diffraction pattern for ultraviolet up to radio waves. for example we don't see light diffraction from glasses.

X-ray and gamma have diffraction through crystals and X-ray is one of must important instrument in crystallographic.
Also in metals we have X-ray diffraction. Gamma and X-ray can pass from surface and see grating. This lead to have diffraction from metals.

I apologize for scribbling English. My language isn't English but i am trying to improve it.
 
I make mistake in above,difference of real part of n and the environment refractive index is responsible of reflection.
 
abbas_majidi said:
The metals contain a see of free electrons. In EM we know refractive index for metals is complex. Imaginary part of n is responsible for absorption and reflection of EM waves.

What do you mean for "imaginary part of n is responsible for absorption and reflection of EM waves" ?
My native language isn't English too.
 
In Electromagnetic theory refractive index of metals(n) obtain as complex number and imaginary part of n arises from absorption of EM waves by metals. In other word complex n is Representative of absorption in matter.
 

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