Debunk me, please #2 (lasers/masers)

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Discussion Overview

The discussion revolves around the behavior of laser and maser beams over long distances, specifically addressing the question of beam spreading and the feasibility of using such beams to etch patterns on Earth from light-years away. Participants explore theoretical implications and calculations related to beam width and diffraction.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether shorter wavelengths lead to greater spreading of laser beams, suggesting that shorter wavelengths may actually diffract less.
  • Another participant provides calculations indicating that to maintain a beam diameter of 15 meters over 10 light years, significant improvements in telescope size or reductions in wavelength would be necessary.
  • A participant references a paper suggesting that a narrow beam could theoretically be focused over hundreds of light years, challenging the idea that a beam would spread too much to etch detailed patterns.
  • Concerns are raised about the practicality of achieving a sufficiently narrow beam width, even with large lenses, citing a proposal involving a Jupiter-sized lens as still insufficient for maintaining a 15-meter beam width at 10 light years.
  • Participants mention specific patterns, such as the Nazca lines and crop circles, in relation to the original question about etching patterns on Earth.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of laser beams over long distances, particularly regarding diffraction and the feasibility of maintaining a narrow beam. The discussion remains unresolved with multiple competing perspectives on the topic.

Contextual Notes

Participants acknowledge limitations in their understanding of the mathematics and physics involved, and some assumptions about beam behavior and practical applications remain unaddressed.

RunDMC
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Hi to all, another debunking request, if I may.

I've heard it said that the shorter the wave used to create a maser/laser the more it spreads out (from high school: 'blue is bent, and brief'). Is that true?

What I'm trying to work out is: could you make a really, really straight laser that would get no bigger in diameter than, say 15 metres over a distance of 10-25 light years? I don't have the maths/physics to work out if a laser/maser would be the size of a house or a planet by the time it traveled such long distances.

[I'm trying to settle a bet about whether those scorched patterns which appear on the side of our planet from time to time could be 'etched' on using a laser/maser from a VERY long way away. Extra brownie points if you can name the scorched patterns I'm thinking of.]

Thanks! :smile:
 
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Hi RunDMC. This and your previous question are appropriate for the regular engineering or physics forums. The Skepticism and Debunking is for fringe subjects - evidence and observations. :smile:
 
Patterns etched on the side of the planet? Hydro electric systems with no dam? Seems fairly fringe to me -- feel free to send me back to skepticism as this thread progresses!

Although I suppose I am asking for real physics knowledge and advice on maser/lasers and (in the other question) angular momentum. Thanks! :smile:
 
RunDMC said:
Hi to all, another debunking request, if I may.
I've heard it said that the shorter the wave used to create a maser/laser the more it spreads out (from high school: 'blue is bent, and brief'). Is that true?
What I'm trying to work out is: could you make a really, really straight laser that would get no bigger in diameter than, say 15 metres over a distance of 10-25 light years? I don't have the maths/physics to work out if a laser/maser would be the size of a house or a planet by the time it traveled such long distances.
[I'm trying to settle a bet about whether those scorched patterns which appear on the side of our planet from time to time could be 'etched' on using a laser/maser from a VERY long way away. Extra brownie points if you can name the scorched patterns I'm thinking of.]
Thanks! :smile:

You have it backwards - shorter wavelengths will diffract less.

For detailed calculations, you might want to look at

http://www.coseti.org/radobs14.htm

For a fully-illuminated 10 meter diameter telescope system, operating at a
wavelength of 656 nm at a range of 10 light years (632,420 A.U.), for which
THETA3 = 0.0138":

D = 0.0381 A.U.

To get to 15 meters, you'd have to increase the telescope size proportionately, or decresae the wavelength.

.0381 Astronomical Units = 5 699 683 800 meters

So you need a *lot* of improvement to get 15 meters at 10 light years

This is using the "FWHM" (full width half maximum) beamwidth, other definitions of beamwidth may give slightly different figures.
 
Thanks for the link

Thanks for the link. The paper seems to suggest you could focus a narrow beam for (theoretically) 100s of L.Y. and maintain or 'focus' a narrow beam.

Darn, my bet had been that a beam would spread far too wide to etch a pattern with features less than 15m in detail from 10-25 LY (based on some pop science I recalled of how big a laser pointer beam would be on the moon). :smile:
 
RunDMC said:
Thanks for the link. The paper seems to suggest you could focus a narrow beam for (theoretically) 100s of L.Y. and maintain or 'focus' a narrow beam.

Darn, my bet had been that a beam would spread far too wide to etch a pattern with features less than 15m in detail from 10-25 LY (based on some pop science I recalled of how big a laser pointer beam would be on the moon). :smile:

And so it will be, unless you have a VERY large lens. Even Robert Forward's proposal of using a Jupiter sized (200,000 km) fresnel focusing lens will give you a beam width that's much larger than 15 m at 10 lightyears at optical frequencies.
 
RunDMC said:
Extra brownie points if you can name the scorched patterns I'm thinking of.]
Thanks! :smile:
The Nazca lines in Peru!
 
Last edited:
Or the Crop circles..lol!
 
As for that part, that's not fringe, that's nuts! :biggrin:

This was a essentially a physics question but I did cringe bit when I moved it.
 

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