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Thread: Burning ants w/magnifying glass and the like...

  1. #1
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    Default Burning ants w/magnifying glass and the like...

    This might be a silly question, but how narrow a beam can be focussed from a 250W hallogen light source? Why is it that laser light is so easily focussed into a beam that is so highly concentrated?

    Sorry if these are dumb questions

  2. #2
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    Lasers are completely different from more "conventional" sources of light, whether those are halogen, standard filament bulb, etc.

    Here's a decent article on the subject:

    http://www.howstuffworks.com/laser.htm
    RR

    Metrologic HeNe 3.3mw Modulated laser, 2 Radio Shack motors, and a broken mirror.
    1979.
    Sweet.....

  3. #3
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    Thanks for that, it make sense now

  4. #4
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    You can focus light from any source into a beam. It is primarily the emitter size and divergence that determines how narrow a beam you can obtain, but it can also depend on the spectral properties of the light. Lasers typically and inherently have low divergence (for example gas lasers) or a small emitter size (laser diodes).

    If the light source is divergent you need to focus it using a lens and/or a reflector. The monochromatic light from a laser is easily collimated into a beam by a lens, but polychromatic light from for example a halogen bulb cannot be collimated as easily, because different wavelengths have different refractive indexes.

    Since laser light is monochromatic, it can in fact be focused to a very small size. The limit is about half the wavelength of the light.

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    For another newbie this leads onto another question... Am I right in saying that you get issues with beam quality by trying to combine too different sources of laser at the same wavelength into a single beam if its not polarised correctly? If this is the case why is this? Is it not a case of light being emitted as single photons,
    or do you need to consider it as you would do with radio waves where two sources of say at 1ghz on the same frequency would cause all kinds of issues if you didnt say polarise them in opposite planes?

    ?!

  6. #6
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    Quote Originally Posted by madgadget View Post
    For another newbie this leads onto another question... Am I right in saying that you get issues with beam quality by trying to combine too different sources of laser at the same wavelength into a single beam if its not polarised correctly? If this is the case why is this? Is it not a case of light being emitted as single photons,
    or do you need to consider it as you would do with radio waves where two sources of say at 1ghz on the same frequency would cause all kinds of issues if you didnt say polarise them in opposite planes?

    ?!
    correct polarization orientation is necessary for optimum throughput of combined beams and has nothing to do with beat frequencies, or interference phenomena, it more so has to do with how polarized light is reflected off of angled surfaces.
    Pat B

    laserman532 on ebay

    Been there, done that, got the t-shirt & selling it in a garage sale.

  7. #7
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    Right ok, still a bit beyond me Ill catch up in time I hope Are Lasers polarised naturally or do the combining cubes for example do this for you? I really don't know how this all fits together yet.

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    Pat B

    laserman532 on ebay

    Been there, done that, got the t-shirt & selling it in a garage sale.

  9. #9
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    Quote Originally Posted by madgadget View Post
    Right ok, still a bit beyond me Ill catch up in time I hope Are Lasers polarised naturally or do the combining cubes for example do this for you? I really don't know how this all fits together yet.
    Some lasers are polarized "naturally" and some are made to be polarized by man. The PBS cube works properly and most effectively when the two polarized lasers are at 90 degree polarization with respect to each other.
    Pat B

    laserman532 on ebay

    Been there, done that, got the t-shirt & selling it in a garage sale.

  10. #10
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    Right ok thats what I would expect. Would polarising a Laser not reject anything that is out of plane and thus loose valuable brightness?

    Examples I have seen of people using PBS cubes show two red Lasers for example sitting on a plate, so I imagine there is a way to polarise the Lasers on the module? Or do people typically not bother?

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