Interference by reflection on a CD

In summary, a focused beam of light projected onto a CD creates a visible interference pattern on a screen, indicating good spatial coherence. This property is evident in lens-focused beams from LED or sunlight, but even less intense color separation can be seen with diffused light reflecting on the CD. A non-coherent light source would not produce such patterns. The concept of coherence must be carefully defined in this context, as it pertains to the phase uniformity of a particular color of light traveling from source to detector. The CD acts as a figured mirror, limiting the path of light and producing different colors depending on the source and observer.
  • #1
MaxLinus
5
0
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.
 

1. What is interference by reflection on a CD?

Interference by reflection on a CD is a phenomenon that occurs when light waves reflect off the surface of a CD and interfere with each other, creating a pattern of light and dark spots. This is due to the difference in path length between the reflected waves, causing them to either amplify or cancel each other out.

2. How does interference by reflection affect the playback of a CD?

The interference pattern created by reflection on a CD can cause errors in the playback of the data stored on the disc. This can result in skips, pops, or distortion in the audio or video being played.

3. What causes interference by reflection on a CD?

Interference by reflection on a CD is caused by the physical structure of the disc, which consists of a layer of polycarbonate plastic with a reflective coating and a protective layer. When light waves hit the surface of the disc, they are reflected and interfere with each other due to differences in the thickness of the layers.

4. Can interference by reflection be prevented?

Interference by reflection on a CD can be minimized by using high-quality materials and manufacturing techniques to create a smoother and more uniform surface on the disc. Additionally, using error correction techniques during playback can help mitigate the effects of interference.

5. Is interference by reflection only a problem with CDs?

No, interference by reflection can occur with other types of optical media, such as DVDs and Blu-ray discs. It is also a common issue in other areas of science, such as in the study of light and optics.

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