very high collimated lens.

Discussion in 'The Projects Forum' started by hiren.dave, Jul 3, 2012.

  1. hiren.dave

    Thread Starter New Member

    Jun 22, 2012
    20
    0
    Hi,

    I want to design a project named "high range laser distance finder". Here, my laser is not collimated and its spread. So i want highly collimated lens that can maintain laser beam to infinite range.

    is it possible? or it must maintain laser beam up to 1 km.
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    More than possible. Laser range finder used in surveying (what you are describing) do it routinely. I used one in the 70's in my surveying class, I doubt they have gotten worse, only better.

    Infinite is stretching it a bit far, but you can go quite long distances.

    Don't use your email-adresses as user name.
     
  3. hiren.dave

    Thread Starter New Member

    Jun 22, 2012
    20
    0
    thanks man.

    is their any beam for laser that can maintain beam width up to 1 km.
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    They make laser range finders up to 20 km or more..
     
  5. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    It is stretching it infinitely far, to be precise. :)

    As you point out, theoretically, a beam always has some divergence. There is no way around this unless the beam is refocused (at some distance away, which is usually not practical) with a proper lens.

    The best results are obtained with a gaussian spatial distribution, which is a diffraction limited beam. Many lasers (most notably single mode gas lasers) will output a high quality fundamental mode which is a diffraction limited beam. However, not all lasers do this. Some have poor beam quality (semiconductor lasers, for example), and some allow other higher order spatial modes which diverge more (cheap gas lasers, and some high power semiconductor lasers).

    So, even the best diffraction limited laser beams will diverge with a small angle, and there is no such thing as a beam that stays collimated over an arbitrary distance.

    I think the trick is to use properly designed lenses to make a relatively wide beam and maintain the gaussian beam profile, so that the divergence will be minimized.

    http://www.rp-photonics.com/beam_divergence.html

    http://www.physics.nus.edu.sg/pc2193/Experiments/lab.pdf

    As far as distance with laser range finders, the longest distance I know of is the example of measuring the distance to the moon using special corner mirrors placed there on the Apollo missions. That's a distance of over 400,000 km measured to accuracies of a few centimeters. Here the beam diverges considerably, but actually this is an advantage, because a narrow beam (if it were possible to make) would be very difficult to aim at a small mirror.

    So the constraint is that you want divergence low enough to allow a strong enough signal to be returned, but not so low that you can't reliably align the laser and hit the target.
     
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