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Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837
Lets say you make a Kerr Cell capable of holding off a MV, it's going to be quite tall ... the electric field is not guaranteed to be even across the entire cell, it depends on the environment. If you shine a laser through part of it, you can determine the electric field at that part and no more.
If you want to even out the field you need known capacitance across the cell which overwhelms the effect of the environment. Which is what those big hunks of metal on the Northstar dividers do ... and that capacitor needs adequate damping to make sure it doesn't ring with series inductance.
Alternatively you could come up with some way to average it out.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
yes you make good points there pinky, until we solve the problems with our current RC-divider set ups, there is little to be gained by moving up to electro-optical methods.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837
I didn't mean to rule it out entirely. Even without evening out the field it is possible, just not easy.
With the Kerr Cell you would basically be forced to measure the electric field at lots of different heights and average them to find the voltage.
Pockels is nicer in this respect, since it provides a linear change in refractive index. If you simply bounce light up and down a pockels cell and measure the time delay between two light beams of different polarizations, the averaging will have been done for you. This is actually used in commercial devices.
Of course traditional pockel cells large enough to hold off high voltage are outrageously expensive. You would need to make your own by poling glass or polymer if you wanted to do it cheap ... quite a project.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837
Hmm, seems I was wrong ... quartz is suitable for a pockels cell for measuring voltages, it's the shutters which require the exotic crystals.
I think you could simply take an X or Y cut slide like this and light it from the thin edge (and cut it into ribbons to get more cells, or to stack them to greater length).
I wonder if the new age synthetic quartz "healing wands" are usable ... this one mentions birefringence, so I assume at least some of them are crystalline quartz ... of course you're just as likely to get something else.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
To get any appreciable length of material you'd probably be best off buying an entire crystal and cutting it up into thin bars ... sizeable investment though. With those MTI wafers a proof of concept is an option on the cheap though polish the sides, get a laser diode and some polarizing film, 2 detectors (split beam is the easiest way to correct for power fluctuations) and away you go.
Although for a high bandwidth device you would need avalanche photodiodes or photomultiplier tubes ... and up goes the price again :/
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DIY High voltage probe
