[Laser] Sky illumination experiment

[S. Schappert]

G'day to the list !

In 1983, I had acquired a fresh a 35 mW Melles Griot HeNe gas laser.  I
lived below the flight takeoff path at JWA and thought it would be cool to
see the 632.8 nm reflect off the tails of outgoing flights.  Dusk was the
best.  This was COOL !

To make a long story short, the two silent-mode helicopters from MCAS Tustin
or MCAS El Toro (AH-64 I presume) that hovered over my darkened house in
Santa Ana Heights made me a believer in God.  Don't play with coherent
light.

I don't care about the "urban myths" or any ones "philosophy" about what
they can and cannot do.  Believe this as fact.

Respect in all cases, from the retina, intra-cavity from HR to OC, SS, DPSS,
metal and gas- output densities are as large as ever today from UV to FIR.

Please keep coherent and bright photon sources contained.  Some pilot, one
day, may thank you.

Best and kindest regards to the list !

-Scott

-----Original Message-----
From: laser-bounces at mailman.qth.net [mailto:laser-bounces at mailman.qth.net]
On Behalf Of Laser @ KatHouse1.com
Sent: Saturday, July 02, 2005 5:39 PM
To: Free Space LASER Communications
Subject: Re: [Laser] Sky illumination experiment

This is an excellent experiment but one which would result in fines where I
live as there is an ordinance against lights shining up into the sky.
However, there is no mention of sky pointed lasers, LEDS, etc. So far!
Probably just an oversight or maybe it's because this is already regulated
by the feds.  Although if idiots continue to shine lasers into the
cockpits of airplanes who knows what may happen in the way of more
restrictions on lasers.

I don't see any harm since it was done only for a brief period of time but
doing this on a regular basis or setting it up to run as some sort of beacon
would probably result in the local astronomy club throwing rocks on your
light bulb(s) as this sort of thing ruins the enjoyment of that hobby which
is already in serious trouble from existing man made light pollution.

Everyone please keep this in mind when pointing lights skyward.  At least
with a laser (or collimated LED)  the illumination is confined to a small
area.   But using bare light bulbs especially without some form of beam
forming lens or reflector is irresponsible.  Unless of course you have no
neighbors, especially any that are interested in astronomy.

Putting an IR filter on the light source is another possibility although
with the enhanced IR sensitivity of CCD cameras that many astronomers are
now using this may not offer much in the way of making the light source less
offensive.

=====

----- Original Message -----
From: "Kerry Banke" <kbanke at qualcomm.com>
To: "Free Space LASER Communications" <laser at mailman.qth.net>
Sent: Friday, July 01, 2005 10:55 AM
Subject: [Laser] Sky illumination experiment


>
> Last evening I finally got around to trying an experiment I have been
> wanting to do for some time.  I have a 1 KVA  Elgar variable frequency AC
> power supply I borrowed from Greg, K6QPV.  I hooked it up to a two tube
48"
> florescent light fixture that I laid on the ground upside down, pointed
> skyward.  I set the supply frequency for 55 Hz which produces a primary
> light modulation at double that or 110 Hz.  I used my laptop running
> Spectrum Lab with a 1 Hz bin and displaying 100-150 Hz.  The receiver
> was  my standard K3PGP low light unit with a 4" lens. The sky was clear
> with a slight bit of haze detectable when viewing hills at 2-4 miles away
.
> This is about as clear as San Diego skies get this time of year.   I went
> to a NLOS location about 1/2 mile away and swept the horizon in the
> direction of my home.  I was able to detect the 110 Hz signal over maybe
10
> degrees Azimuth & elevation. As seen in my NLOS Laser experiments, the
> clear sky signal is maximum at the horizon towards the source. The signal
> was only about 5-10 dB above the noise but was easily identifiable.  This
> was the first step towards trying a higher power experiment with hopefully
> a 400 W Sodium Vapor lamp. The estimated light output from the florescent
> tubes is about 5600 lumens ( assuming about 70 lumens/watt for two 40 watt
> tubes.  400 watts of High Pressure sodium vapor lamp could provide around
> 40,000 lumens and if I can be lucky enough to find a  400W Low Pressure
> Sodium lamp, up to 72000 lumens. This approach should allow communicating
> with any of the multi-tone communication programs.
>   - Kerry N6IZW -
>
> _______________________________________________
> Laser mailing list
> Laser at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/laser




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