EM wave interacting with refelcting surface

In summary, the conversation discusses the concept of reflection in electromagnetic waves and how the electric and magnetic fields of the incoming light can penetrate into the reflecting medium. The diagrams shown demonstrate the reflection point and the behavior of the fields at the surface. The conversation also mentions the concept of ordinary and extraordinary waves and how they behave differently at the surface. The idea of frustrated total internal reflection and TIRF microscopy is also mentioned as a way to study the evanescent fields that penetrate the second medium. Overall, the conversation highlights the complexity of analyzing reflection as an electromagnetic phenomenon.
  • #1
modulus
127
3
When trying to explain reflection through the EM treatment of light waves, how do we account for the fact that the electric/magnetic field of the incoming light would penetrate into the medium from which it is reflecting off of?

Diagrams like these:

Fig13.gif


show the 'reflection point' on the axis of propagation. But, the fields which propagate about that axis would penetrate into the other medium.

From what I understand, EM waves are essentially coupled electric and magnetic fields that 'go on creating each other'...if one of the two gets distorted (the one in the plane of the normal and incoming light wave), wouldn't it destroy the light wave?
 
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  • #2
What do you mean by "get distorted"? Do you mean the decrease of the number of lines or dots in the reflected and transmitted wave in that picture? That's just for telling us that the amplitudes of the TE and TM components are reduced by virtue of the energy conservation. And as long as the fields in both region satisfy the wave equation, we will still have a wave.
 
  • #3
blue_leaf77 said:
What do you mean by "get distorted"? Do you mean the decrease of the number of lines or dots in the reflected and transmitted wave in that picture? That's just for telling us that the amplitudes of the TE and TM components are reduced by virtue of the energy conservation. And as long as the fields in both region satisfy the wave equation, we will still have a wave.
I find the diagram confusing. The incoming energy is a mix of ordinary and extraordinary waves, not TM and TE waves. The ratio of Magnetic to Electric is always constant for the material in which it is travelling, so that will alter in the glass.
modulus said:
When trying to explain reflection through the EM treatment of light waves, how do we account for the fact that the electric/magnetic field of the incoming light would penetrate into the medium from which it is reflecting off of?

Diagrams like these:

Fig13.gif


show the 'reflection point' on the axis of propagation. But, the fields which propagate about that axis would penetrate into the other medium.

From what I understand, EM waves are essentially coupled electric and magnetic fields that 'go on creating each other'...if one of the two gets distorted (the one in the plane of the normal and incoming light wave), wouldn't it destroy the light wave?
I find the diagram slightly confusing. The incoming ray can be regarded as a mixture of two light waves - in the plane of the paper and at right angles to it. The two behave differently at the surface, so we can study them separately. Each wave has magnetic and electric fields in a fixed ratio. For the wave in glass, the ratio is different to that in air.
 
  • #4
tech99 said:
I find the diagram confusing. The incoming energy is a mix of ordinary and extraordinary waves, not TM and TE waves.
Why do you think that it's a mix of ordinary and extraordinary waves? That terms only arise in the propagation inside an anisotropic material.
 
  • #5
I am not talking about the specific diagram. I am speaking in general about how to analyse reflection as an electromagnetic phenomenon. The thing is that the propagating electric field should penetrate beyond the reflecting surface (for the TM wave), and this should cause a polarisation to occur. With this added polarisation, won't the time varying electric field 'as seen by the light wave' be different from when it normally propagates? Wouldn't this cause the wave to reflect unevenly back?
 
  • #6
modulus said:
When trying to explain reflection through the EM treatment of light waves, how do we account for the fact that the electric/magnetic field of the incoming light would penetrate into the medium from which it is reflecting off of?

<snip>

Google 'frustrated total internal reflection" or "TIRF microscopy". The incident field does indeed penetrate the second medium (it's an evanescent field).
 

1. How does an EM wave interact with a reflecting surface?

When an EM wave encounters a reflecting surface, it can either be absorbed, transmitted, or reflected. The interaction between the EM wave and the reflecting surface depends on the properties of the surface, such as its composition and texture, as well as the wavelength and angle of incidence of the EM wave.

2. What happens to the EM wave when it is reflected off a surface?

When an EM wave is reflected off a surface, it changes direction and bounces off the surface. The angle of reflection is equal to the angle of incidence, and the amplitude and frequency of the EM wave remain unchanged. The reflected wave can then interact with other surfaces, causing multiple reflections.

3. Can an EM wave be completely absorbed by a reflecting surface?

No, an EM wave cannot be completely absorbed by a reflecting surface. Some of the energy of the EM wave will always be reflected or transmitted, depending on the properties of the surface. However, the amount of reflection can be minimized by using materials with special properties, such as anti-reflective coatings.

4. How does the texture of a reflecting surface affect the interaction with EM waves?

The texture of a reflecting surface can greatly affect the interaction with EM waves. A smooth surface will cause specular reflection, where the reflected wave is parallel to the incident wave. A rough or uneven surface will cause diffuse reflection, where the reflected wave is scattered in many directions. The texture can also affect the amount of reflection, with rougher surfaces typically causing more scattering and less reflection.

5. What role do the wavelength and angle of incidence play in the interaction between an EM wave and a reflecting surface?

The wavelength and angle of incidence of an EM wave are important factors in the interaction with a reflecting surface. The wavelength determines the size of the wave and can affect how it interacts with the surface's texture. The angle of incidence affects the direction of the reflected wave, with a steeper angle resulting in a greater change in direction. The wavelength and angle of incidence can also determine whether the wave is reflected, transmitted, or absorbed by the surface.

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