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Green lasers: how much power is too much?

  1. Jun 28, 2009 #1
    I saw some green lasers on dealextreme recently, they have units that go up to 200 mW:
    http://www.dealextreme.com/details.dx/sku.1997

    This thing looks a bit unsafe to me! My intention is to show the daughters some stars here in our polluted skies, not much else. How much power is needed for that? How much is dangerous? I will be the only one handling the device, so I am not concerned with someone pointing the laser at their friends' eyes (I treat the tool like a firearm).

    Thanks for any advice.


    Moderator note -- Laser pointers are dangerous; please use with extreme care. See warning.
     
    Last edited by a moderator: Apr 24, 2017
  2. jcsd
  3. Jun 28, 2009 #2

    Hurkyl

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    Wouldn't it be easier, and more accurate, to take a field trip?
     
  4. Jun 28, 2009 #3
    The laser would be even more important then! There will be enough stars that they won't know to which one's I'm pointing!

    The neighbours also like to bug me with "Where is *** now" and "which star is that bright one" so I think that a laser would be great for these instances.

    Are the 5 mW lasers adequate? Would I be much happier with a 20 mW or even 50 mW model? Are they really that dangerous when used for their intended purpose?
     
  5. Jun 28, 2009 #4

    turbo

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    There is currently a nice special running at OPT, offering some decent binoculars, a green laser, and a red flashlight for $29.95 plus S&H. If you live in a light-polluted area, this would be a good kit to show people around. Some astronomy clubs are snapping up multiples of these kits as "outreach resources". I just ordered a kit for myself, despite the fact that I already have a nice pair of Nikon binos and some red flashlight/chart-lights. My neighbor's grand-daughters are very interested in nature, and the laser-pointer will be handy to show them around the sky.

    http://www.optcorp.com/product.aspx?pid=10245 [Broken]
     
    Last edited by a moderator: May 4, 2017
  6. Jun 28, 2009 #5
    My 5 mW green laserpointer works fine, the beam is extremely bright. On cloudy days you can even shine on a cloud and with binos see a green spot on the cloud!

    A few weeks ago I used it to point out the M51 galaxy to a friend who is too lazy to study a detailed finder's chart. I look through my binos and point with my laserpointer exactly at the spot where M51 is and then wait until the friend has the beam in his view. Then I point out a pattern of four stars that surround M51 which are visible in direct vision in the bino.

    Then I tell in words where M51 is relative to these stars and I point with my laserpointer again at M51. Then I ask him to use his averted vision in order to see something that looks like an extremely faint cloud where M51 is supposed to be.
     
  7. Jun 28, 2009 #6

    Pengwuino

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    Isn't 200mW approaching industrial cutting power?
     
  8. Jun 28, 2009 #7

    Integral

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    If so it is at the very lower end. I have worked with 30W green Coherent lasers for ablating Si. I believe that the same family of lasers go up to 50W. This is in a 3mm beam, we focused the beam to 30Micrometer diameter to cut through Si Wafers.
     
  9. Jun 28, 2009 #8

    Pengwuino

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    Yah it definitely wouldn't actually cut anything or engrave, but I imagine it's overkill for just a pointer. Actually looking at the rest of the site, it does seem quite powerful for a pointer.
     
  10. Jun 28, 2009 #9
    Warning, don't buy one of those newwish lasers. They may be rated at 200mW, but only 5-15mW is 532nm green, the rest is infrared caused by the lack of a inrared filter that can harm your eyes bigtime. I would just type in green laser pointer on ebay and get a 5mW one that will look the same only about 8$ shipped. Anything over 5mW is illegal in the USA now which is quite sad. But when you get it you can dissasemble it and turn the potentiometer in it to squeeze out some more juice. But beware as you can burn the diode out easily. Any more questions let me know.
     
  11. Jun 29, 2009 #10
    Thanks, guys. As I understand it green is not a good cutting wavelength. Red might be, though.

    Bass, can you tell me more about the infrared filters? I see the infrared warnings, but I do not really understand them. Can I purchase a laser with an IR filter? I don't see them anywhere.

    Thanks!
     
  12. Jun 29, 2009 #11
    I see that some of the lasers warn that they have no IR filters. But at a fixed 532nm wavelength, what IR is there?
     
  13. Jun 29, 2009 #12
    The laser work with dpss technology. Double the wavelength is shot into a crystal that is halved to create the green. A lot of IR gets through and a lens with a special coating is used to filter it out. If you really want a good laser that is very very quality then try wickedlasers. You will see the price difference for a quality laser with pure green power is a big difference.
     
  14. Jun 29, 2009 #13
    I did look at their site: there is an order of magnitude difference in price.
     
  15. Jun 29, 2009 #14
    One thing you don't have to worry about is the recoil when you switch the laser on. :smile:
     
  16. Jun 29, 2009 #15
  17. Jun 29, 2009 #16
    How is a powerfull green laser going to help you show your daughters stars? you plan on pointing out the star with the laser? Dosen't quite work that way.
     
  18. Jun 29, 2009 #17

    turbo

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    Have you ever used a laser pointer at night? The laser's beam is visible, especially from the rear, and when you give the name of a star and point to it with the laser, It allows the kid to get a point of reference, and reinforce it with a look at a star-chart. They are very handy tools for getting people familiar with the night sky.
     
  19. Jun 29, 2009 #18
    I stand corrected
     
  20. Jun 29, 2009 #19
    Actually the pointer and observer see the laser beam off till a certain height. If you do point it at a star, the observer will actually see what star you are pointing too. That is if the observer is near the pointer.
     
  21. Jun 29, 2009 #20

    turbo

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    Yes, that is trivial. It is a whole lot more effective than pointing your finger, though, and if you have the observer stand in back of you, the accuracy of the pointing is remarkable.
     
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