[Laser] IR laser Array???

Sat, 11 Jan 2003 20:07:26 -0000

Jim
Thanks for that, all points noted. and safety issues  will be implemented
when operating  - will let you know how I get on.
List appears  quite quiet at the moment?

              Thanks again
                             Dick G8BYI

----- Original Message -----
From: "n9jim-6" <[email protected]>
To: <[email protected]>
Sent: Saturday, January 11, 2003 5:55 PM
Subject: Re: [Laser] IR laser Array???

> 1) A few years ago we had an debate about  power addition.
> In terms of pure power present at a non-correlated receiver, this will
> increase the received power in areas where the beams overlap. However,
> there will be phase differences in each  tx-rx path. So in a correlated
> receiver, they do not add.
> (this is what I can remember)
>
> A simple experiment that I just ran...
>
> Using a silicon detector (power meter with a diffuser) I measured 2
> different laser pointers individually:
> Laser A - 5.6 mW
> Laser B - 2.4 mW
>
> applying both lasers on the same detector at the same time resulted in:
> 8.0 mW
>
> Conclusion: A+B works for non-correlated detectors (Si PIN diodes)
>
> 2) Safety
> a) aircraft
> We've been advised to never point any laser of any power at aircraft,
> even class 1 (eye safe).  Why? because IF it is seen by a pilot, it can
> distract him (dazzle).  Its not for eye safety but flying safety.  Do
> you believe this?  If you have ever set up a long distance (10+ miles)
> thru air experiment with a simple laser pointer, you know this is real!
>  A couple years ago, a friend and I set up a MCW (tone on off keying)
> experiment.  One end was up on a hill outside town (VERY DARK).  The
> other was in the middle of  a 1 million+ metro area, among the lights.
>  This was a distance of 10-12 miles. When he finally got "on target"
> that <5mW RED laser was the brightest thing anywhere in the metro area!
> No other light source could compare. A good approximation is that a 5mW
> laser is roughly equivalent to a 5KW bulb.
> b) IR
> IR has the advantage of not being "seen". So dazzle effects are
> eliminated.  However, eye damage is not.  So if  power levels exceed
> class 1 damage may occur, and no eye blink response exists for class 3a
> protection. So power density level at the aircraft must be "eye safe".
> Some detectors can see IR: night vision goggles, most B&W cameras, some
> military aircraft sensors.
> So there is the potential for an issue should an aircraft pass through
> the signal path.
> BOTTOM LINE: if an aircraft appears to be coming close to the signal
> path... stop transmitting until it is clear.
>
> Jim
>
>
> Richard Burrows wrote:
>
> >Hi
> >Has anyone done any experiments using several CD type IR lasers to
increase power levels without collimation or large lens.
> >I have seen LED arrays being talked about and used by Hams, but have
found only complex University type schemes for laser arrays using complex
wavefront feedback methods.
> >I have a lot of old CD laser diodes  circa 2-5mw that I thought I could
use on a straight forward :) array ! Anyone got any thoughts on this
please.Or am I wasting my time?
> >I want to use such an array for cloud/troposcatter over the horizon BPSK,
that's the aim anyway.
> >Another question re Safety and Aircraft/helicopters. If low power IR were
used the dazzle effect on pilots eyes is not there, but are there any
instrumentation on aircraft that might be effected?
> >Obviously Police TV spy in the sky cameras could be a problem.
> >
> >                          regards
> >                                 Dick G8BYI
> >
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