Fast-assed signal switch

[Phil Hobbs]

the mixing at 1x, which gets you a cool 126 dB improvement, and the

*ahem* 132 dB. Never mind--it's a nice big bite for an afternoon's work.

Cheers,

Phil Hobbs

 

[John Larkin]

It's true that lasers in general, and especially solid state lasers like
Ti:Sapphire, aren't triggerable any time you happen to want. Their
jitter, though, is lower than any other known system whatever--below 1
part in 10**20, iirc. You can make them wider than an cctave, so that
you can harmonically lock one end of the frequency comb to the second
harmonic of the other end, and make something like an old-time ham
marker frequency generator, producing peaks at 100 MHz intervals across
the whole visible and near-infrared spectrum, whose frequency is known
to an accuracy of 10**-18 or better. The key to the accuracy is that
you aren't multiplying up the 100 MHz by 4,000,000 times--you're doing
the mixing at 1x, which gets you a cool 126 dB improvement, and the
frequency accuracy of each comb peak (in Hz) is the same as the rep
rate's.

This got Jan Hall and Ted Haensch the Nobel Prize in 2005--more for the
optics than the electronics, because they figured out how to do the
spectral broadening without messing up the time coherence. The nice
thing is that once they figured it out, it's really easy to do.


There are also streak cameras, which can take data continuously, not
stroboscopically like a sampling scope, and can display sensibly at 1
ps/division. Getting the electrical signal onto the optical one is
usually the tough part, but I have an electrooptical modulator in my lab
that is flat to 1 dB out to 30 GHz, and the technology could go further.
Full scale is about +20 dBm.

If you get good enough coverage this way, it could work. Alternatively,
with a fs sampler, you could use a variable optical delay, but that
would probably have to be mechanically scanned, which would make the
update rate slowish.


Cheers,

Phil Hobbs

Hamamatsu makes a sampling scope that takes an optical input into a
photocathode and then sweeps the electrons, streak-tube-style, across
an aperature into a photomultiplier. They demoed it for me at the
factory in Hamamatsu [1] but, in typical sampling-scope style,
couldn't get it to work.

John

[1] Worth the trip, if ever you get the chance. It's an immaculately
clean, nicely laid out factory, with everybody wearing slippers, with
blue gas flames everywhere. Sort of a cross between Silicon Valley and
Hell.

 

[Phil Hobbs]

It's true that lasers in general, and especially solid state lasers like
Ti:Sapphire, aren't triggerable any time you happen to want. Their
jitter, though, is lower than any other known system whatever--below 1
part in 10**20, iirc. You can make them wider than an cctave, so that
you can harmonically lock one end of the frequency comb to the second
harmonic of the other end, and make something like an old-time ham
marker frequency generator, producing peaks at 100 MHz intervals across
the whole visible and near-infrared spectrum, whose frequency is known
to an accuracy of 10**-18 or better. The key to the accuracy is that
you aren't multiplying up the 100 MHz by 4,000,000 times--you're doing
the mixing at 1x, which gets you a cool 126 dB improvement, and the
frequency accuracy of each comb peak (in Hz) is the same as the rep
rate's.

This got Jan Hall and Ted Haensch the Nobel Prize in 2005--more for the
optics than the electronics, because they figured out how to do the
spectral broadening without messing up the time coherence. The nice
thing is that once they figured it out, it's really easy to do.

There are also streak cameras, which can take data continuously, not
stroboscopically like a sampling scope, and can display sensibly at 1
ps/division. Getting the electrical signal onto the optical one is
usually the tough part, but I have an electrooptical modulator in my lab
that is flat to 1 dB out to 30 GHz, and the technology could go further.
Full scale is about +20 dBm.

If you get good enough coverage this way, it could work. Alternatively,
with a fs sampler, you could use a variable optical delay, but that
would probably have to be mechanically scanned, which would make the
update rate slowish.


Cheers,

Phil Hobbs

Hamamatsu makes a sampling scope that takes an optical input into a
photocathode and then sweeps the electrons, streak-tube-style, across
an aperature into a photomultiplier. They demoed it for me at the
factory in Hamamatsu [1] but, in typical sampling-scope style,
couldn't get it to work.

Right, that's the streak camera back end. Perfect for looking at
optical signals between about 300 and 900 nm, but much less useful
otherwise, due to the O/E conversion problem.

John

[1] Worth the trip, if ever you get the chance. It's an immaculately
clean, nicely laid out factory, with everybody wearing slippers, with
blue gas flames everywhere. Sort of a cross between Silicon Valley and
Hell.

I've been to Japan once, about 10 years ago, but although I gave it a
first-class try for a whole week, I couldn't learn to like raw fish.
I'm also 6'4" and 260 pounds, so 14 hours in an economy class seat is a
good approximation to Purgatory. (Back then, IBM had a sensible
policy--you were allowed to go business class if the flight was over 8
hours. My ticket from JFK to Narita was $5k.)

Cheers,

Phil Hobbs

 

[Robert Latest]

[1] Worth the trip, if ever you get the chance. It's an immaculately
clean, nicely laid out factory, with everybody wearing slippers, with
blue gas flames everywhere.

Actual flames? What for?

robert

 

[Spehro Pefhany]

[1] Worth the trip, if ever you get the chance. It's an immaculately
clean, nicely laid out factory, with everybody wearing slippers, with
blue gas flames everywhere.

Actual flames? What for?

robert

Glasswork would be my guess. They make PMTs and other types of vacuum
(and gas) tubes.


Best regards,
Spehro Pefhany

 

[John Larkin]

[1] Worth the trip, if ever you get the chance. It's an immaculately
clean, nicely laid out factory, with everybody wearing slippers, with
blue gas flames everywhere.

Actual flames? What for?

robert

Glasswork would be my guess. They make PMTs and other types of vacuum
(and gas) tubes.

Yup, they're melting glass everywhere. They even have lathes that use
flames instead of cutting tools.

The photocathode activation is cute. A PMT has its seal-off tube still
in place, and it's in a light box, and powered up into a microammeter.
Very home-made, with fluorescent tubes for the calibrated (?) light
source and old needle-type meters, 6 or so tubes at once. Inside the
sealoff tubes are little boats full of caesium compounds or whatever,
and there's a flame under part of each tube. The operator uses a
magnet to slide the boats in and out of the hot section of the tube,
evaporating the photocathode stuff onto the inner surface of the tube,
and maybe the dynodes too. Lots of skillful juggling gets six tubes
tuned up in one session.

They make one pmt that looks like a basketball. They're the ones that
exploded (thousands of them) at a water-filled neutrino detector.

http://www.fnal.gov/pub/ferminews/ferminews01-11-23/p1.html

http://jp.hamamatsu.com/resources/products/etd/eng/html/pmt_005.html


John

 

[John Larkin]

Alright, excellent. Then, to apply this to things I have on hand, I
might... hmm, I probably have some signal schottkies. I have some RF
circuits, one board here has four glass body diodes arranged in a ring
modulator (inbetween two ferrite transformers- could it be any more
obvious?). I can make out "HP2", and maybe "305" on the next line. HP2305,
any ideas?

Anyway, for pulse generator, I don't recall having any diodes with
reasonable snap, so I might try an avalanche generator. 2SA1206 or
something, I discovered, works at bench supply voltages, while I have some
PH2369's that plink from +100V, as Jim uses in AN47. So I could set up one
of these on, say, 6" of shorted coax, no, twisted pair -- so that when this
thing fires, it runs a good voltage for a moment, then reflects back and
shorts out. In the mean time, some schottkies or whatever are biased by
said pulse and pick up some input from across the input cable, passing it to
something, which I suppose has to be a charge amp, to restore the frequency
response.

Ironically, looking at the finer details of an avalanche generator is one of
the goals of my wanting to look at hell ass fast signals. Fortunately I
have more than two 2369's...

Tim

The earliest commercial samplers, the Lumatron junk and the Tek N,
used an avalanche pulser and a single diode sampler, which was very
nonlinear and kicked a huge pulse out the input. HP's first sampler
was an avalanche pulser too, at 700 MHz. They used it to accidentally
discover the SRD, and soon they used srd's and got to 1 GHz, then soon
to 4 GHz with a dual-diode feedback sampler.

Tek's 7S14 dual-trace sampling plugin, much later, used an avalanche
pulser with no srd. It was sold as a 1 GHz gadget but was typically
twice that. They used mercury batteries to bias off the sampling
diodes (a full 4-diode bridge, I seem to recall) and they are a
nightmare to replace, so few functional units still exist. Too bad,
they were very nice, with signal delay lines and excellent internal
triggering.

John

 

[Robert Baer]

John Larkin wrote:


[1] Worth the trip, if ever you get the chance. It's an immaculately
clean, nicely laid out factory, with everybody wearing slippers, with
blue gas flames everywhere.

Actual flames? What for?

robert

Glasswork would be my guess. They make PMTs and other types of vacuum
(and gas) tubes.

Yup, they're melting glass everywhere. They even have lathes that use
flames instead of cutting tools.

The photocathode activation is cute. A PMT has its seal-off tube still
in place, and it's in a light box, and powered up into a microammeter.
Very home-made, with fluorescent tubes for the calibrated (?) light
source and old needle-type meters, 6 or so tubes at once. Inside the
sealoff tubes are little boats full of caesium compounds or whatever,
and there's a flame under part of each tube. The operator uses a
magnet to slide the boats in and out of the hot section of the tube,
evaporating the photocathode stuff onto the inner surface of the tube,
and maybe the dynodes too. Lots of skillful juggling gets six tubes
tuned up in one session.

They make one pmt that looks like a basketball. They're the ones that
exploded (thousands of them) at a water-filled neutrino detector.

http://www.fnal.gov/pub/ferminews/ferminews01-11-23/p1.html

http://jp.hamamatsu.com/resources/products/etd/eng/html/pmt_005.html


John

Don't you mean "imploded"?

 

[John Larkin]

On 20 Aug 2007 08:33:31 GMT, the renowned Robert Latest


John Larkin wrote:


[1] Worth the trip, if ever you get the chance. It's an immaculately
clean, nicely laid out factory, with everybody wearing slippers, with
blue gas flames everywhere.

Actual flames? What for?

robert

Glasswork would be my guess. They make PMTs and other types of vacuum
(and gas) tubes.

Yup, they're melting glass everywhere. They even have lathes that use
flames instead of cutting tools.

The photocathode activation is cute. A PMT has its seal-off tube still
in place, and it's in a light box, and powered up into a microammeter.
Very home-made, with fluorescent tubes for the calibrated (?) light
source and old needle-type meters, 6 or so tubes at once. Inside the
sealoff tubes are little boats full of caesium compounds or whatever,
and there's a flame under part of each tube. The operator uses a
magnet to slide the boats in and out of the hot section of the tube,
evaporating the photocathode stuff onto the inner surface of the tube,
and maybe the dynodes too. Lots of skillful juggling gets six tubes
tuned up in one session.

They make one pmt that looks like a basketball. They're the ones that
exploded (thousands of them) at a water-filled neutrino detector.

http://www.fnal.gov/pub/ferminews/ferminews01-11-23/p1.html

http://jp.hamamatsu.com/resources/products/etd/eng/html/pmt_005.html


John

Don't you mean "imploded"?

Don't be a PITA. Nobody likes a PITA.

John