From: robblack@ix.netcom.com
Date: Wed, 22 Oct 1997 22:00:15 +0000
To: Pinhole Listserv <pinhole@exploratorium.edu>
Subject: Re: Pinhole Daily Digest
To Cathy Saito,
Laser light is special in part because it is collimated-more parallel
than the light emitted from most bulbs. Rather than spreading out in
all directions (and thus losing intensity with the square of the
distance) the light is directed in a beam. The light does spread out,
though, and loose intensity; and the diode laser in a laser pointer
speads out much more quickly than does the beam from a gas (HeNe)
laser. In fact if you look carefully, you will probably notice that the
beam of the diode laser is oval, spreading out more in one direction
than the other, while that of a HeNe laser is round. One activity my
students have enjoyed is finding the relationship between distance to a
screen and beam diameter.
Most (all?) gas laser have a long tube, the resonance chamber, with
mirrors at both ends. One mirror is totally reflecting and the other is
~97% reflecting. Photons must bounce back and forth within this chamber
in order to "lase" and escape out of the partially reflecting mirror.
The tube is quite long in relation to its diameter, only rays travelling
at very small angles will make it from the back mirror out the far end.
Good luck with your observant 9th graders!
Heidi Black <robblack@netcom.com> <hblack@exploratorium.edu>
Teacher-in-Residence