Tuning the Laser
Didn't we learn that you need to have exactly the right color of light to make
an atom do that?
Yes, each type of atom responds only to exactly the correct color. A big part
of the difficulty in making laser cooling work was to get enough light of just
the right color. For this you need lasers for which you can adjust the color
very precisely to match the color that the atom wants.
If the color is wrong the photons just go right through the atoms, and it is
difficult to get the color just right!
Yes, that is just what happens with real atoms and lasers, except that a real
atom is even pickier than the ones in this demonstration. Just the vibrations
in the floor of a normal building make the color of a laser change so much it
doesn't match the atoms any more. Scientists have to work very hard to make
the laser light stay the proper color.