Collimating incoherent light emitted by a LED

  1. Hello,

    What would be the best method to "collimate" light from a LED with an emitting area of 12mm^2 and a maximum divergence angle of 80° with minimal loss of light intensity?

    I want to collimate it into a beam of approximately 5-10mm.

    I have an aspheric condenser lense at hand with an effective focal length of 13.7mm. This lens succeeds in making the beam spherical, with a diameter of approximately 30mm at the focal length, but it still undergoes significant divergence. I have tried adding more positive lenses into the optical system to try, but I can't seem to create such a small beam diameter without losing a great portion of the emitted lighted.

    Is there any particular lense configuration I could use?

    Thanks.
     
  2. jcsd
  3. mfb

    Staff: Mentor

    I think it is hard to keep a significant fraction of light in the beam, unless you add a lense every 2-5 cm or something similar. You cannot reduce the phase-space size of your light, no matter how the setup looks like.
     
    Last edited: Nov 21, 2012
  4. Andy Resnick

    Andy Resnick 6,019
    Science Advisor
    Education Advisor

    I agree with mfb- the large size of the emitter restricts your ability to collimate the beam at even a moderate diameter without lossy beam shaping (spatial filtering, for example).

    Over what range does the beam need to be 5-10mm in diameter?
     
  5. there is no limit as to distance, as I have a lot of mirrors available and a lot of workspace. what is the best way to reduce the amount of light lost? I managed to "collimate" it to a diameter of about 10mm, but in order to do so I used a setup similar to a pinhole and I lost a lot of light. but to me at this stage a pinhole seems the way to go...
     
  6. davenn

    davenn 3,981
    Science Advisor
    Gold Member
    2014 Award

    to ask the obvious.....

    why not just use a laser LED ?? already collimated with built in lens :)

    Dave
     
  7. i want to try and use a LED instead!
     
  8. You´re perfectly right about the pinhole.
    The standard way of producing a parallel beam used to be:
    Use a lens to produce a (reduced) image of your light source onto/into a pinhole. Try to capture as much of the light as possible.
    On the other side of the pinhole, use a lens to produce your collimated beam. Then you use autocollimation to adjust the position (and tilt) of the lens for minimal divergence (and beam position). Beam size adjustment requires a diaphragm.
    But of course you will lose a lot of light this way. You can vary the pinhole size for the best compromise.
    And you´d better use an optical bench or an optical table for mechanical stability.
     
  9. "no limit as to distance" implies zero power from an incoherent source, even if there were no diffraction.

    A laser diode would be limited by diffraction. You get one diode in each CD or DVD reader-burner.
     
Know someone interested in this topic? Share this thead via email, Google+, Twitter, or Facebook

Have something to add?