Crazy thing happens when I play with my laser

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Discussion Overview

The discussion revolves around the observation of unexpected patterns produced when a strong green laser is aimed at a mirror and the resulting reflections are analyzed. Participants explore the underlying physics, including potential interference effects and scattering phenomena.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes observing a bright beam and a "crazy pattern" on the wall when the reflected beam is aimed to intersect with the original beam.
  • Another participant suggests that the observed pattern is due to light interfering with itself, proposing that the pattern is circular when a beam interferes with itself.
  • A different participant notes that the pattern appears even when the beam does not directly touch itself, indicating a more complex interaction.
  • One participant hypothesizes that the interference pattern may be generated from the two interfaces of the mirror and suggests testing with tin foil to see if the pattern persists.
  • Another participant proposes that the observed pattern could be an Airy pattern resulting from scattering off a small particle, rather than interference.

Areas of Agreement / Disagreement

Participants express differing views on the cause of the observed patterns, with some attributing it to interference and others suggesting scattering effects. No consensus is reached on the exact explanation.

Contextual Notes

Participants note challenges in capturing the phenomenon visually, which may limit the ability to analyze the patterns further. The discussion also highlights the dependence on the specific properties of the reflective surfaces used in the experiments.

Who May Find This Useful

Individuals interested in optics, laser physics, and experimental physics may find the exploration of interference and scattering phenomena relevant to their studies or experiments.

beholderseye
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I have a strong green laser, about 200 mw. I discovered this a long time ago and have wondered why it does this ever since...

I shine my laser at a mirror. It bounces back, with a brighter beam. That's not what confuses me. What confuses me is when I try to aim the bounceback beam to perfectly intersect with my current beam, I get this CRAZY pattern on the wall right behind my hands:

2459801-blue-water-abstract-background-with-circular-wave-ripple-pattern.jpg


Kind of like this, but the waves get closer and closer together the further from the center.

I am so confused and confounded by this. Can someone explain the physics behind this?
 
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I can't speak on the specifics of the situation without a picture of the 'ripples', but what is happening is that the light is interfering with itself which causes an interference pattern, I believe the pattern is circular when a beam is interfering with itself, which would explain this.
 
Its weird though, because the pattern, while strongest when the laser hits itself, appears even when the beam is not touching itself but still being reflected off of the mirror.
 
Very hard to get a picture of it too.
 
beholderseye said:
Very hard to get a picture of it too.

do it anyways, but the answer is interference.
 
beholderseye said:
Very hard to get a picture of it too.

I don't blame you!


I can imagine why that happens, and to me it definitely sounds like self-interference.
 
Managed to get a video of it.

https://www.youtube.com/watch?v=http://youtu.be/38U2Evzb8jw

 
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I would suspect that an interference pattern is being generated from the two interfaces of the mirror.

Try doing the same experiment with the shiny side of tin foil instead of a mirror. I would expect the pattern to be not present if the above hypothesis is true.
 
It looks like an Airy pattern, which is what you would get when scattering off a small particle.

If the laser is powerful enough, it can form a defect which it then scatters off in the manner that you recorded in your youtube video.

In short, it is likely scattering off a point-like source rather than interference per se.

Claude.
 

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