0
$\begingroup$

I've had it in my head for a while that collimation requires both monochromacity and coherency. However, lately I've started thinking about it and I can't really see why coherency is required for collimation. But I've not been able to find anything to say either way since it monochromatic light sources pretty much all produce coherent light. Could anyone provide clarification?

$\endgroup$
1

1 Answer 1

0
$\begingroup$

I am assuming you are asking this from a practical point of view, i.e. collimation using lenses. If so, I think monochromaticity is the only requirement. Having different wavelengths would lead to optical aberration, which prevents perfect collimation.

$\endgroup$
4
  • $\begingroup$ Yes. Because the focal point for a single lens is different for each wavelength right? So you would need multiple monochromatic sources each positioned properly which pretty much can't happen if you have one source emitting multiple wavelengths. Although I thought tripelet loupes used 3 lens elements to correct for chromatic abberation so I am not sure why this isn't done for collimation. I'm probably misunderstanding something. $\endgroup$
    – DKNguyen
    May 23, 2021 at 5:06
  • $\begingroup$ @DKNguyen Yes, pretty much. I'm not familiar with triplet loops, so can't say what they do. $\endgroup$
    – Yejus
    May 23, 2021 at 5:13
  • 1
    $\begingroup$ @DKNguyen Triplets can eliminate chromatic aberration for 3 specific wavelengths, which gives a very good visual (or photographic) result, but there's still some residual aberration for other wavelengths. There's info about that here: en.wikipedia.org/wiki/… but I should warn you that the style of that article isn't easy to read. $\endgroup$
    – PM 2Ring
    May 23, 2021 at 6:03
  • 1
    $\begingroup$ @PM2Ring Oh I see. So a tripelet just kind of approximates it to the point where our eyes don't notice, I guess. $\endgroup$
    – DKNguyen
    May 23, 2021 at 17:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.