Coherent Light Waves: Interference & Diffraction Explained

[GrizzlyBat]

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?

 

[negitron]

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.

 

[GrizzlyBat]

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.

 

[Andy Resnick]

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?