[Laser] Use of crystal spheres, aka clear marbles

[laser@mailman.qth.net]

For what it's worth, from another part of the laser hobby:

Frank DeFreitas at www.holoworld.com works on another side of lasers,
their use
for holograms.

This is a very interesting site.

To our point:  When an amateur holographer wants to make a very fine
point
source for amateur holograms, he or she can take the output of a laser
pointer,
send the wide beam through a clear marble (crystal ball ...) and it will
emerge
on the other side as a very concentrated point source for the laser
light needed
for the hologram to be made.

Using this approach, any light coming from one side of a crystal
"marble" will
emerge on the other side in a very precise (and much smaller and
concentrated)
spot on the other side.  Since the light from a mirror is essentially
coming
from a narrow place, the light emerging on the other side of the crystal
sphere
will be in essentially one spot.

If the diode detector is placed in contact with the spot, a very small
surface
area of diode can be illuminated with a concentrated bit of energy.

Now, quite forgivingly, the light from the mirror will emerge on the
other side
of the sphere (clear marble) in just about the same spot no matter how
rough the
focus!  In other words, 1) the light doesn't even have to be tightly
focussed,
and 2) it does not need to be precisely "on center".

Tom Upton
AD6N