[time-nuts] Now For Something Completely Different...GPS Security

J. Forster jfor at quikus.com
Fri Feb 14 10:14:02 EST 2014


There was a lot of work done on GEN III NV devices. They use GaAs
photocathodes w/ high QE. The same photocathode works for PMTs.

Detecting single photons is duck soup w/ a PMT. With modest cooling, you
can get the dark count down to 1/minute or better.

-John

=================


> On Fri, Feb 14, 2014 at 7:45 AM, J. Forster <jfor at quikus.com> wrote:
>
>> You should not denigrate PhotoMultiplier tubes.
>>
>> They are virtually perfect, almost noiseless, detectors. With the right
>> photocathode, they are capable of QEs >50%, spectral response from the
>> VUV
>> to near IR, and dark counts <1 PPS, with maximum count rates >10 MPPS.
>> Thay can easily have current gains of >10E+6
>>
>
> Really? I used to work on photon-counting systems for photometric
> astronomy. As I recall, the best quantum efficiency I had ever seen was
> around 21%. Which cathode material are you talking about?
>
> Conversely I remember working on current amps for photodiodes. The
> photodiodes I was playing with had QEs of 90% but, of course, they had no
> current gain. Detecting individual photoelectrons is a challenge.
>
> Yeah, PM tubes are very cool devices, especially if you cool them to
> reduce
> the emission of thermal electrons. ;-)
>
> --
> Brian Lloyd, WB6RQN/J79BPL
> 706 Flightline Drive
> Spring Branch, TX 78070
> brian at lloyd.com
> +1.916.877.5067
>




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