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Thread: Help. Parallel / collimated laser beam

  1. #1
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    Default Help. Parallel / collimated laser beam

    Hello
    I need a laser diode that emits parallel / collimated laser beam.
    Reason : I need to aim the laser dot at a target about 500 meters away.
    What should I consider FAC lens or collimating lens or something else ?
    Thank you.

  2. #2
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    What size "dot" do you need at the destination?

    Do you need any particular power or wavelength / colour?
    - There is no such word as "can't" -
    - 60% of the time it works every time -

  3. #3
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    Quote Originally Posted by danielbriggs View Post
    What size "dot" do you need at the destination?

    Do you need any particular power or wavelength / colour?
    Hello Daniel and thank you for your reply,

    About my question : the dot should be round 2 to 3 mm in diameter (approx) OR square 2 mm (approx) each side.
    Power :3W (I try to burn a match)
    Wavelength : 980nm (I need invisible light)

    I bought a 808nm diode (this number is stated by the seller) but I can see the dot - It's a weak red dot. Then I bought a 980nm diode with FAC lens. This time, I can't see the dot. I need a camera to "see" the dot but the farther I move the laser diode away from the screen the less focused the dot is
    Last edited by Kwan; 07-13-2019 at 09:02.

  4. #4
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    swamidog is online now Jr. Woodchuckington Janitor III, Esq.
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    getting a 3mm spot at 500 meters away is going to be pretty much impossible.

    Quote Originally Posted by Kwan View Post
    Hello Daniel and thank you for your reply,

    About my question : the dot should be round 2 to 3 mm in diameter (approx) OR square 2 mm (approx) each side.
    Power :3W (I try to burn a match)
    Wavelength : 980nm (I need invisible light)

    I bought a 808nm diode (this number is stated by the seller) but I can see the dot - It's a weak red dot. Then I bought a 980nm diode with FAC lens. This time, I can't see the dot. I need a camera to "see" the dot but the farther I move the laser diode away from the screen the less focused the dot is
    suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.

  5. #5
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    Quote Originally Posted by swamidog View Post
    getting a 3mm spot at 500 meters away is going to be pretty much impossible.
    Hello Swamidog,

    I have a laser pointer like the below. It emits a small laser dot inside my palm, the same small red dot on a wall far away.
    I need a laser diode can make the same dot
    Why it is impossible ?
    Thank you
    Attached Thumbnails Attached Thumbnails Apollo_MP_600Q_MP_600Q_Quartet_Mini_Keychain_850180.jpg  


  6. #6
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    Sorry, "Physics" says no

    Diffraction will limit the minimum spot size you can focus to at a given distance. This is also wavelength dependant, so the minimum spot size is greater for an IR laser than a visible or UV for example.

    Further reading:
    Beam quality / Beam parameter product / M^2 of a laser
    Diffraction limited beams


    A very good laser might have a divergence of 1mRad for example. Most are much higher, especially multi mode diodes.
    So, at a distance of 500m this would be about 0.5m in diameter
    And 3W at that power density isn't going to burn anything.
    - There is no such word as "can't" -
    - 60% of the time it works every time -

  7. #7
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    Quote Originally Posted by swamidog View Post
    getting a 3mm spot at 500 meters away is going to be pretty much impossible.
    As well as with 980nm stupid dangerous, not fun dangerous

  8. #8
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    Use a squib to do it electrically.

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