🚀 go-pugleaf

I am not sure if you were wondering about this per se, but:
 
You cannot see the "beam" of any laser save for unimaginably powerfull 
ones best not mentioned unless the beam passes through smoke or fog 
or something else to bounce off and scatter through. This is true to 
the extent that air is transparent to the beam, which is usually for 
all practical purposes. (if life in this newsgroup has taught me one thing 
it is to qualify my statemnets to the point where they say nothing)
 
If smoke or dust is in the plan, I recoomend a tube of at least 10 mW, 
these and power supplies that run off batteries, well, you can't buy them 
at the grocery store yet, but if you hang around the surplus market for 
any length of time there comes a point where you can't get away from them! 
 
For casual classroom pointing something of less power would likely be in order, 
there are in fact regulations for such things. 
 
Price on tubes varies with power, quality, and history, I have seen little tubes 
assured to work sell for $19. Tubes around 5 mW hover near $100. 
 
I see here a 10mW tube and AC PS for $200...
 
Battery op'd power supplies are a bit costly because everyone wants them, 
$100 or $125 for a surplus commercial unit that is flexible and powerfull, 
less for wierd stuff.

-cornhead