Re: Double concave mirror toy

[Tim Folkerts <tfolkert@FHSU.EDU>]

At the risk of restating what many may already know, I think Ludwik &
Robert have two different experiments in mind.  Ludwik seems to be thinking
of a photon-photon interaction, while Robert is aiming the laser at the
object (at least as it is seen in the lens).


                |                          ...<  Laser
   __object     |               __     ....
  /  \          |              /  X....
-|----|---------+-------------|....|----------------------------
  \__X <..      |        ....  \__/
          ...   |    ....    real image
             ...|....                          :-) viewer
              lens


If the laser is aimed "through" the image and toward the lens, it will
continue on to illuminate the point marked X on the object.  This light
will reflect in various directions, and the the image will show this, by
lighting up at the corresponding point.  This seems to be what Robert is
intending.





                |                     .<  Laser
   __object     |               __  ..
  /  \          |              /  \.
-|----|---------+-------------|-..-|----------------------------
  \__/          |              \._/
                |            ..   real image
                |          <.                   :-) viewer
               lens



Of course, as Ludwik supposes, the real image itself cannot interact with
the laser.  If the laser isn't aligned to hit the lens, the object isn't
illuminated, and the real image is not illuminated.  Although the real
image is visible, the effect isn't.  (At high enough intensities, I believe
there are some photon-photon interactions, but that is a different matter
altogether).

Robert wrote:
> You won't see any laser light on the image if you cannot see the image in
> the first place.  ...  It should produce a dot of light on the
> image.  Why shouldn't it?