Interference by reflection on a CD

  • #1
MaxLinus
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TL;DR Summary
Interference by reflection on a CD implies coherence?
A fairly focused beam of light incident on a CD projects a clearly visible interference pattern onto a screen.
May I infer that it has good (or at least enough) spatial coherence?
This property is evident, for example, in a lens-focused beam of light produced by a LED or by a ray of sunlight that filters directly through a half-closed window.
Nonetheless, less intense colour separation can be seen even when diffused light reflects on the CD (or soap bubbles, or oil stains on a rainy day). Would a completely non-coherent light produce such patterns?
 
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  • #2
Addendum. Found a partial answer in this paper: Coherence properties of different light sources and their effect on the image sharpness and speckle of holographic displays
 
  • #3
One must be very careful to define what one means by coherence. In this case one is interested in the phase uniformity for a particular color of light traveling the multiple paths from source to detector required for interference. The CD is a figured mirror. The path of light onto the CD then into your pupil is limited both by the size of your pupil and the characteristics of the source. Your eye will see colors from a diffuse source. A point source will produce colors that project onto a wall. But a diffuse source will not project colors onto the wall.
 

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