[Laser] blue pointer

[Dave]

> Date: Thu, 15 Apr 2010 19:16:14 +0200
> From: w.fritz at htp-tel.de
> Subject: [Laser] Blue pointer
> To: laser at mailman.qth.net
> Message-ID:<20100415191614.5bz15bxeldi8gog0 at webmail.htp.net>
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> 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.

That's what I was thinking, although the blue beam may be a bit better
for a tracking pointer, due to the ability to see the beam from the side due
to the increased atmospheric scattering.

> 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.

That's getting close to being ultraviolet.  Close, but not quite. 
Still, it should
cause an interesting fluorescence in quite a few materials.

> With 6x Blu Ray writer diodes, there will be around 200mW or maybe a
> little bit more possible.

I've seen some demonstrations where these have been used for popping
balloons from a distance.  That's scary!

> 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.

Yes, quite interesting.

> 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.

Impressive!

> 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.

Ultraviolet light is notorious for causing cataracts in the human eye, 
but usually
only at high power levels and for prolonged exposures.  Mostly.  It can 
also cause
conjunctivitis, a VERY painful irritation of the cover of the eye.  But, 
does anyone
really want to take the chance?

As for the dangers of lasers, as someone who has intentionally stared 
into the
business end of a 20 Watt Argon laser, I can tell you that it's 
incredibly bright;
even a 150 milliSecond pulse is enough to instantly fuse/cauterize eye 
tissue
I had laser surgery for a detached retina, with a truly great retinal 
eye specialist
surgeon.  I have a really nice photograph now of what that amount of 
power will
do to a human retina.  It's not something I'd want to experience outside 
of the hands
of a very skilled surgeon!  Let's be careful.

> Vy 73
> Wilfried, DJ1WF

Dave
WA4QAL