Why does a divergent lens create an interference pattern?

In summary, the conversation discussed the use of a green laser pointer with a divergent lens and the emergence of a clear interference pattern on the screen. The distance from the laser did not affect the pattern. The speaker suspects that the pattern is generated within the laser pointer and is surprised that this is also seen in published works. They also mention possible issues with the laser diode lens and consider using other laser diodes. It is noted that all finite lenses and mirrors generate interference patterns, with smaller lenses producing smaller patterns. This is a well-known phenomenon in amateur astronomy.
  • #1
qnt200
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I used a green laser pointer (λ = 532nm). I aimed it at a divergent lens that has a focus of -50cm. The distance from the laser does not play a big role. As a result, a very clear interference pattern with a series of concentric circles appeared on the screen.
I did not find a suitable interpretation for this simple experiment.
 

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  • #2
I suspect that the interference (or diffraction) pattern is generated within the laser pointer.
 
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  • #3
.Scott said:
I suspect that the interference (or diffraction) pattern is generated within the laser pointer.

Thanks for the reply. I think you are right. After looking at the laser point in more detail, it can be seen that on at least one side the pattern is in the form of concentric semicircles, while on the other side it is difficult to see. I also took off the chrome metal protection, but that didn’t help. Obviously the problem is either in the laser diode lens or in the laser diode? I am especially surprised that the same laser pointers are used in some published works. I have two, and both show the same symptoms. I don’t know if it’s possible to fix it somehow or better get some other laser diodes?
 
  • #4
All finite lenses and/or mirrors generate interference patterns. The larger the lens, the smaller the patterns. This is very well known in practice to amateur astronomers as stars will always be tiny sets of rings, not dots, in a small telescope using high magnification.

The lens on a laser diode is tiny. Interference fringes are to be expected.
 
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Related to Why does a divergent lens create an interference pattern?

1. Why does a divergent lens create an interference pattern?

A divergent lens creates an interference pattern because it causes the light waves passing through it to diffract and interfere with each other. This creates areas of constructive and destructive interference, resulting in a pattern of light and dark bands.

2. How does a divergent lens cause diffraction and interference?

A divergent lens is curved in such a way that it causes the light waves passing through it to spread out, or diffract. This diffraction leads to the waves interfering with each other, resulting in an interference pattern.

3. Can a divergent lens create both constructive and destructive interference?

Yes, a divergent lens can create both constructive and destructive interference. The areas of constructive interference appear as bright bands, while the areas of destructive interference appear as dark bands in the interference pattern.

4. What factors affect the interference pattern created by a divergent lens?

The interference pattern created by a divergent lens can be affected by several factors, including the wavelength of light, the distance between the lens and the light source, and the curvature and thickness of the lens.

5. How is the interference pattern of a divergent lens different from that of a convergent lens?

The interference pattern of a divergent lens is different from that of a convergent lens because the two types of lenses have opposite curvatures. A divergent lens causes the light waves to spread out and create an interference pattern, while a convergent lens causes the light waves to converge and create a focal point.

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