Can a Laser Light Be Magnified with a Magnifying Glass?

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Discussion Overview

The discussion revolves around whether a laser light can be magnified using a magnifying glass, with participants exploring the implications of brightness, intensity, and the optical properties of lasers and lenses. The conversation includes technical aspects of optics and personal experiments with lasers.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants question the meaning of "magnify" in the context of laser light.
  • One participant suggests that focusing a laser beam can increase its intensity but not its brightness, referencing the conservation of brightness.
  • Another participant proposes using high-quality optics, such as microscope objectives, to focus a laser beam effectively.
  • A participant expresses uncertainty about the efficiency of mirrors in a setup designed to bounce a laser beam and considers using a magnifying glass to enhance the beam's brightness.
  • Some participants discuss the theoretical implications of Archimedes' mirror trick and its relation to modern solar power technologies, with differing opinions on its feasibility.
  • Concerns are raised about the safety of using powerful lasers, particularly regarding accidental reflections.
  • There is a debate about whether adding more mirrors can increase brightness, with references to thermodynamic principles and the concept of radiometric brightness.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the effects of using a magnifying glass with a laser or the implications of brightness conservation. Multiple competing views remain regarding the effectiveness of mirrors and the theoretical aspects of Archimedes' mirror trick.

Contextual Notes

Participants express various assumptions about the definitions of brightness and intensity, as well as the practical limitations of optical components. The discussion includes unresolved questions about the relationship between mirror quality and light loss.

ehummel
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Hi all, can a laser light be magnified by means of a magnifying glass?
 
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What do you mean, exactly, by "magnify"?
 
Hi, i am referring to making the beam brighter by focusing the beam to a smaller beam like when one focuses sunlight thru a magnifying glass.
 
Yes you can - but a laser beam is generally already pretty small and you would need fairly good optics for the focussing down to win over optical errors scattering light out of the beam.
A microscope objective would work, a dollar store magnifying glass wouldn't.
 
ehummel said:
Hi, i am referring to making the beam brighter by focusing the beam to a smaller beam like when one focuses sunlight thru a magnifying glass.

"Brightness" is a conserved property of a source of light. Note that 'brightness' has a specific radiometric definition that is different than the common use of the term.

Focusing a beam with a lens increases the intensity (technically, the radiant incidance) but not the brightness.

Conservation of brightness is why Archimedes' mirror trick doesn't work.
 
English Please... I have a little handheld green laser that I want to mount on a board with mirrors that will bounce the beam back and forth. This laser is very bright to the eye. You can see the beam very well in a shadowed area or at night. This laser will actually light a match. but I was thinking that by the time it is reflected 4 or 5 times, there would be a lose due to the inefficiency of the mirrors. I don't know much about optics so I may be totally off base with this thought. I was thinking that if I introduce a magnifying glass at the point where the visual brightness of the beam drops off, i could get a few more bounces out of it. If this sounds totally stupid, forgive me.
 
BTW: what is Archimedes' mirror trick? Sounds interesting...
 
mgb_phys said:
Yes you can - but a laser beam is generally already pretty small and you would need fairly good optics for the focussing down to win over optical errors scattering light out of the beam.
A microscope objective would work, a dollar store magnifying glass wouldn't.

Sorry, i missed your response. OK, this pretty much answers my question. I have a couple of old microscopes laying around. I think I may try that. Thank you.
 
ehummel said:
I don't know much about optics so I may be totally off base with this thought. I was thinking that if I introduce a magnifying glass at the point where the visual brightness of the beam drops off, i could get a few more bounces out of it.
Nope, you can squeeze the beam down to make the point brighter but at the other side of the minimum point the beam spreads out - it doesn't restore any of the light lost by the mirror bounces.
The mirror's are losing light because of reflection losses and because they are not perfectly flat and so some light is being scattered out of the beam.

ps. Be careful a laser that can ignite matches can easily damage your eyesight with even an accidental reflection from a shiny bit of metal like a watch strap or a dropped part.
 
  • #10
mgb_phys said:
Nope, you can squeeze the beam down to make the point brighter but at the other side of the minimum point the beam spreads out - it doesn't restore any of the light lost by the mirror bounces.
The mirror's are losing light because of reflection losses and because they are not perfectly flat and so some light is being scattered out of the beam.

ps. Be careful a laser that can ignite matches can easily damage your eyesight with even an accidental reflection from a shiny bit of metal like a watch strap or a dropped part.

So the best thing i can do is have the highest quality mirrors possible and or have a more powerful laser.

BTW: Yes, I caught 1 of those accidental reflections 1 time. It is NOT a toy!
 
  • #11
ehummel said:
BTW: what is Archimedes' mirror trick? Sounds interesting...
Archimedes death ray: http://en.wikipedia.org/wiki/Archimedes#The_Archimedes_Heat_Ray_.E2.80.93_myth_or_reality.3F

In any case, I don't agree with that answer: the death ray idea works just fine in theory and in modern reality because the more mirrors you have, the more light you can gather. "Brightness" is not constant, it is directly proportional to the number of mirrors. It didn't work for Archimedes because it is impossible for a bunch of people to simultaneously manually aim mirrors (no one will know which bright spot is theirs).

The exact concept is used for concentrating sunlight for solar power:
http://www.google.com/imgres?imgurl...TI0OII&sa=X&oi=image_result&resnum=3&ct=image
 
  • #13
Andy Resnick said:
No. Radiometric brightness (sometimes also called the etendue) is a conserved quantity.

http://en.wikipedia.org/wiki/Etendue

http://en.wikipedia.org/wiki/Radiance

Archimedes' death ray is impossible in principle due to thermodynamic considerations, which I have discussed in previous threads.
Maybe we're just talking past each other here. Are you saying that you can't make a "bright" spot by reflecting some sunlight with a mirror, then make it brighter and hotter by adding more mirrors? [edit]...or a magnifying glass or large telescope, for that matter (except that the mirrors in the solar tower are flat).

How does this idea differ from a solar furnace or solar power tower, for example? I'll do a search and see if I can figure out what you mean from other threads...
 
Last edited:
  • #14
For a solar tower there is obviously a maximum temperature you can reach = the blackbody temperature of the source.
But I'm not clear there is a power limit based on the area of mirrors or the solid angle of the sun (other than practical limitations).
 

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