Coherent Light Waves: Interference & Diffraction Explained

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Discussion Overview

The discussion revolves around the concepts of coherent and non-coherent light waves, particularly focusing on their implications for interference and diffraction. Participants explore the definitions of coherence, the conditions under which interference effects can be observed, and the differences between coherent light sources like lasers and non-coherent sources.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question the nature of non-coherent light sources, suggesting it may relate to the organization of light waves and their interference effects.
  • One participant explains that coherence involves photons being in phase and that interference effects are more pronounced with coherent sources, such as lasers, but can also be observed with ordinary light sources.
  • Another participant speculates on the use of non-coherent light in experiments like Young's slit, suggesting that while diffraction may occur, a laser would likely produce clearer results due to more waves being in phase.
  • A participant introduces the idea of two types of coherence: spatial and temporal, linking them to different types of interferometers and emphasizing the statistical nature of coherence.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and interpretation of coherence and its effects on interference and diffraction. There is no consensus on the implications of using non-coherent light sources in specific experiments, indicating ongoing debate.

Contextual Notes

Participants mention different types of coherence and their relevance to various experimental setups, but do not fully resolve the implications of these concepts or the conditions under which interference is observable.

Who May Find This Useful

This discussion may be useful for individuals interested in the principles of optics, particularly those exploring the differences between coherent and non-coherent light sources and their effects on interference and diffraction phenomena.

GrizzlyBat
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So is this the ability for light waves to add up and subtract interms of interference? But I am confused as to what a non-coherent light sorce would be. I mean is it when the light waves are not organised enough? So there is no effect of interference through diffraction? or is it that there is interference, but we see the averaged effect and it is not that great?
 
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Coherence simply means that photons with the same wavelength are in phase, as it were. And yes, interference effects are easier to see with a coherent light source, such as a laser. Nevertheless, interference effects can be seen with ordinary light sources--the colors one sees on the surface of a soap bubble or an oil slick, for example, are caused by destructive interference.
 
Yeah, that makes sense. So if I was to use a non-coherent light source, and did youngs-slit experiment, I should see diffraction? or do I have to use something like a lazer? I would think that I could use either but the laser would be more effective. Because more waves would be in phase to start with.
 
There are two main 'flavors' of coherence: spatial and temporal. Temporal coherence relates to the spectral bandwidth, while spatial relates to the size of the source.

Mach-Zender type interferometers work via temporal coherence, while Young-type interferometers work via spatial coherence.

Coherence, as a concept, is a statistical statement- if you know what the value of the field is here and now, how well can your predict the value over there at some future time?
 

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