[Laser] Blue pointer

[w.fritz at htp-tel.de]

Hello Dave,
if they are DPSS based there are the same disadvantages like the green  
ones, but lower effiency.
Beside the lower efficiency the atmospherical attenuation increases  
with decreasing wavelength.
So the blue signal will be weaker some miles away than a red one when  
both sources have the same optical output.
But the higher attenuation might be a challenge, especially because  
there are some cheap 405nm diode lasers built originally for HD-DVD or  
Blu Ray drives.
With 6x Blu Ray writer diodes, there will be around 200mW or maybe a  
little bit more possible.
Another point is, the light source dimensions (the laser chip) are  
smaller in Blu Ray diodes than in the classic red ones.
This allows you to focus the spot better, the spot will be smaller in  
the distance, the optical output covers a smaller surface. So you get  
a higher energy concentration with the same lens (if the lens  
transmission is the same in red and blue). And that circumstance will  
compensate the higher attenuation a little bit. A very interesting  
field for some experiments.
We did a noise free TV transmission via 405nm over a distance more  
than 31km with 5mW taken from a PS3 Blu Ray diode in May 2008.

http://home.arcor.de/W_Fritz/Laser/BluRay/405engl.html

But 405nm is really dangerous. You won't see how much output is really  
present, because the human eye ist very insensitive in this range.  
405nm will cause some chemical degradations beside the classic thermal  
damage if the beam or its reflections hits the eye from low distances.  
So please everybody be very careful if you use such lasers. It is very  
interesting, but a great risk, too.
Vy 73
Wilfried, DJ1WF