[Laser] Re: The EME light pollution.

[F1AVYopto at aol.com]

Tim

>That is a really interesting  experiment. I think we all
>want to hear more about it when you get more  info. Are you
>sure there are not any 60hz power grids near France  that
>the signals could have come from? But even if they came
>from  a nearby country it is still a major deal to be able
>to detect them  reflected in earth-shine from the moon.

We are not absolutely certain  there are not any 60 Hz power grids near 
France but we never found before 120 Hz  in the background light from the sky.
The 120 Hz detected signal was  extremely weak during our experiment with 
Spectran.
A 120 Hz spurious  induction stays always possible but the 120 Hz line just 
appears when the moon  disc crosses over the photodiode and not before and 
after...
We think the  best condition is may be not during a total moon eclipse.
During a "d" half  moon crescent in winter (10 to 12 days after new moon) the 
120 Hz detection  could be easier.
During a total moon eclipse the earth daylight ring gives a  rather strong 
orange light background that gives also a very strong extra  noise.
During the "d" half crescent in winter the moon is above the USA near  6 H TU 
and the background in the dark crescent part can be extremely weak.
We  have a project with the F8DO 30 cm telescope by using a big moon picture  
projected behind the ocular.
With this system we think it will be easier to  isolate the photodiode from 
the bright crescent area and so avoid noise and  saturation effect.
A very narrow optical dielectric filter centred on the  sodium rays stays 
mandatory.
The central wavelength of the all-dielectric  Fabry-Perot filters will shift 
lower in wavelength with an increase in the  incident angle. 
When these devices are used with spherical lenses or  mirrors, the filtering 
frequency shifts versus the convergent angles into the  conical beam increase 
the global bandwidth.
The city lights spectral sodium  rays are mainly from 560 to 620 nm.
The high pressure sodium lights give  double lines on 568 nm, 589 nm (very 
strong), and 615 nm.
If you use the  following filter with a 25° max external conical obliquity 
the bandwidth could  be  optimal.

http://cgi.cafr.ebay.ca/Optical-Filter-595AF60
-Orange-Emission-TRITC-by-Omega_W0QQitemZ3836765982QQihZ017QQcategoryZ3179QQtcZphotoQQcmdZViewItem

73  QRO  Yves F1AVY   Marius F8DO