Learn more physics!
Several years ago, some of us (my friends and I) were trying to construct a low level, inexpensive laser. We settled eventually on using mirrors as the cheapest, though it would take some mathematical equations to get the angles right. We never got around to building it, but I would like to know if the idea would work. The light entered through a one-way mirror in the top. (I dont know if that was necessary, as if the angle was right, it shouldnt come back out.) Next it hit an angled mirror, off of which it shot straight forward. On its way out, it would pass through three focusing glass plates, like those used in microscopes. It would taper as it got down to the end, where it would come out through a hole. Assuming all of the calculations are precise and everything is in place, would this work, and if not, why?
Heres a little picture of it, but I dont know if itll show up right:
| | |
| | |________________________
| | | | | |
|\_ |---------| | | | \ The Laser
Yeah, like that.
- The Builder of Things (age Old)
Indianapolis, IN, US
Dear Builder- the contraption you've described is basically a
telescope, or something like it. Light comes in over a wide area, and
gets focused down to a smaller area. There's a basic tradeoff in any
device like this. If you focus down to a very small area, then the
light will be spread out over a big range of directions. If you want
the light to travel in a small range of directions, you'll need a big
wide beam. The only way you can get a narrow beam with a narrow range
of directions is by throwing out most of the incoming light, say when
it hits the plate with the little hole. Incidentally, the one-way
mirror has a major drawback- nonexistence. The things that get called
one-way mirrors are just partially reflecting mirrors, with one side
kept light and the other kept dark.
A laser works in a completely different way- one that only makes
sense via quantum mechanics. Something in the laser (often, individual
atoms) has a set of special states each with a specific value of
energy. One of the "excited states" (states with more energy than the
"ground state", which has the least) has no easy way to dump its energy
and fall to the ground state. There's some way of pumping energy in
excite atoms to higher states so that they trickles down to that
special state. Then they release energy mainly when triggered to do so
by their environment- a process called stimulated emission. What makes
the light unusual is that the stimulated light comes out at the same
frequency, direction , etc as the light that stimulated it. So the
light can come out in the narrowest range of directions and positions
allowed by basic physics. There's still a trade-off between getting the
beam narrow at some point and getting it to travel a long way before it
spreads out, but the beam is much closer to being an idealized ray than
anything you can get from ordinary light sources.
(republished on 07/28/06)
Follow-up on this answer.