Science Questions

Can lasers be concentrated with lenses?

Sat, 30th Oct 2010

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Question

Joshua Hill asked:

I want to know if you can take ten already very powerful lasers, shoot into the edge of a magnifying concave lens that shoots them into the edge of another lens of the same kind and keeps doing so a couple times and then directing them out of a final lens in a single concentrated beam that could easily burn through paper in less than a second.  Does not need to be ten, just more than one.  If you cannot demonstrate, that's fine.  Just want to know what would happen.

Answer

Dave -   Well, the simple answer is yes.  It’s done all the time.  Virtually any laser which you've seen cutting anything would’ve been focused with a lens.  In fact, the beautiful thing about laser light is it’s far more focusable that ordinary light.  It essentially behaves as if it was coming from a very, very small point source so you can focus it very, very, very tight and it works beautifully.  Focusing multiple lasers into the same beam is much more difficult.   You can focus lots and lots of different lasers in to the same place so you can get lots of crossing focused laser beams onto a single point which is what certainly the American government is trying to do for nuclear fusion things.  They put little tiny pellets of frozen hydrogen, deuterium, into the focus of these hugely powerful lasers.  That then compresses it so much that it can actually get so hot – far hotter than the centre of the Sun - that the hydrogen atoms start fusing and form helium, and you can produce an immense amount of energy that way and they're trying to get energy out of it.  But actually, focusing two laser beams exactly on top of each other is always impossible.

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