[Laser] Re : Re : NLOS contact

[f1avyopto at aol.com]

 You are fully right !

 Using a blue laser in point to point experiment could only be done with a very large beam expender and a very low power density.
Less than 0.01 mW/mm² in all the entire beam points seems a maximum without to be fully safe.
All the experiments with lasers are dangerous and critical.
It is why we did all our laser experiments with not visible infrared lasers and very high diameter beam expender at the TX side.
In a well illuminated 100 mm in diameter output lens a 100 mW laser gives about 1/100 mW mm² that reduce strongly the eyes exposure hazards over 900 nm in a (not focusing) divergent beam.
For communications experiments with the blue light, LEDs seems the best choice !
Lasers for NLOS communications are only the best for bouncing tests on very far and very small targets. 
For NLOS on large clouds layers LEDs are a good choice for safety ! 
73 Yves


 

 

-----E-mail d'origine-----
De : riese-k3djc <riese-k3djc at juno.com>
A : laser <laser at mailman.qth.net>
Envoyé le : Vendredi, 4 Février 2011 20:11
Sujet : Re: [Laser] Re :  NLOS contact


whats the status o using the extremely high power ultra blue laser

friend of mine has one and is fraid of turning it on

it will heat a spot on your hand in just a few seconds

I suspect they may not be entirely legal



Bob K3DJC

On Fri, 4 Feb 2011 17:16:26 +0000 (GMT) Garnier Yves <f1avy at yahoo.fr>

writes:

> Hi Stuart

> Direct forward scatter via Rayleigh scattering seems to me very 

> difficult with a red or an infrared laser in clear air conditions.

> We never succeed with it.

> It's quite possible with an hazy sky and a very flat TX RX aiming 

> axes angle via the Mie scattering effect.

> In fact that is very similar the cloud bounce way ! 

> Rayleigh scattering could be very strong by clear sky with a blue 

> laser.

> A blue sensitive photomultiplier tube at the RX side could be a good 

> choice.

> But...this link could be under the 10 Km range because the blue 

> diffusing air effect will produce also a strong propagation loss in 

> the laser beam.

> Many experiments to do...?  

> 73

> Yves F1AVY

> http://f1avyopto.wifeo.com

> 

> 

> --- En date de : Ven 4.2.11, I <stuart.wisher at talktalk.net> a 

> écrit :

> 

> > De: I <stuart.wisher at talktalk.net>

> > Objet: [Laser] NLOS contact

> > À: laser at mailman.qth.net

> > Date: Vendredi 4 février 2011, 13h47

> > 

> > Thanks for the links Yves,

> > 

> > 

> > 

> > All your contacts seem to be by reflection, whether off

> > mountains, clouds or meadows. My modest contact was by

> > forward scatter since we could not find a reflecting site

> > between us.

> > Have you tried contacts by scatter? I could not get all

> > your info to load and translate so I am unaware if you have

> > tried this mode.

> > Maybe we will try this again by cloudbounce after reading

> > of your excellent results using that mode.

> > As I mentioned, I have a 200mW red laser so we will try for

> > a contact with a coherent signal next

> > 

> > 

> > Regards,

> > 

> > 

> > Stuart G8CYW

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> 

>       

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