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    Re: Lunar laser eye safety
    From: Peter Monta
    Date: 2018 Jun 15, 03:51 -0700
    Hi Paul,

    .. about 6000 times greater than the figure I calculated above.

    Sounds pretty safe, but I wonder about speckle.  The 3-meter Lick telescope has a diffraction-limited spot on the Moon of only 200 meters diameter.  The trip through the atmosphere ruins that performance, broadening the spot to a few km, but with bright speckles inside that still have structure on this 200-meter scale.  I don't know the statistics of how much beam power could wind up in a single speckle, but it's probably only a fraction of a percent with a big 3-meter beam.  Actually, even with all the power in a 200-meter spot (which would never happen), the safety factor is still greater than 20.

    The only thing to do is to repeat the experiment with fresh observers!

    But unless I miscalculate, that would not be a serious error. On the
    Moon, 35 seconds of latitude is about .3 km. If the spot radius is 1.5
    km, the landing site should still be in the beam — ?

    Yes.  Perhaps it was the timing window that was the real problem on that first attempt rather than the pointing.


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