Focusing a Laser Diode

Discussion in 'The Projects Forum' started by odm4286, Aug 21, 2016.

  1. odm4286

    Thread Starter Active Member

    Sep 20, 2009
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    Hello everyone, I want to use a laser diode in a homemade barcode scanner. In order to concentrate the light on a small area(UPC segment .33mm I believe), would it be enough to place a material over the focusing lens that has a small hole drilled through it?
     
  2. #12

    Expert

    Nov 30, 2010
    16,261
    6,768
    It seems that way to me, but I don't remember seeing any bar code scanners with a beam 0.013 inches in diameter.
    I'm going to buy food today so I'll check while I'm there.
    This thing I googled seems to say you are right about using a very small beam.

    "Resolution is normally expressed as the width that a given scanner can resolve down to: medium resolution is usually viewed as around 0.15mm - 0.19mm."

    http://www.barcode.ro/tutorials/barcodes/laser-scanners.html
     
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  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    899
    Look up: diffraction

    Your pinhole could make the focus much worse:
    upload_2016-8-21_12-49-24.png

    Source:
    www.physics.montana.edu
    You would not only get reflection from the center, but from each ring.

    John
     
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  4. odm4286

    Thread Starter Active Member

    Sep 20, 2009
    155
    5
    Interesting, I'll have to keep experimenting. At this point, I think software compensates for the beam size in most scanners
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I think what you need is to collimate it to help account for different distances. But even that may not be necessary. Do you know what your beam divergence is?
    So long as the laser beam is not too big, you will get peaks and troughs as it transits the barcode. As you say, that can be handled in software. Just think of it as finding exo-planets by the transit method. ;)

    John
     
  6. RichardO

    Well-Known Member

    May 4, 2013
    1,231
    382
    A "raw" Laser diode does not have a round beam, it is oval. Some Laser modules have the optics to make the beam round and collimate it as well. I don't hve a feel for what the beam diameter from one of these modules is.
     
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