kerr/pockels effect shutters

[knoxissimpler]

does anyone here know anything about kerr [or pockel, they do the same thing] effect shutters? I found one tut on them, but it is from a sciam from a long time ago, and I was hoping to find more details on their construction first... I do a lot of high speed photography, and have been hoping to do some shots [not some, a LOT] in broad light and I need a VERY fast shutter to do this...

 

[Struan Gray]

The ones I have used send the light through quite a long cylinder of material (10cm long, 8mm diameter) . The cylinder is too long and thin for wide-scale imaging, and the big slab of optical material will add humungeous amounts of spherical aberration to any lens put behind it. When used as a shutter, they depend upon a high-extinction polariser, and that too will not work properly for wide-field imaging.

They are really intended for 'infinity light': parallel rays or a laser beam. They could, for example, be integrated into an 'infinity conjugate' microscope, like the high-end research microscopes sold by Zeiss, Nikon and others, but they would not work properly in a conventional microscope, even if you could cram them within the tube length.

Plus, they need high-bandwidth high voltages to drive them: you will need mains power. Not, I'm afraid, a solution for the field.

 

[knoxissimpler]

well, actually these shutters were common before digital high speed came, and in fact were used to photograph the atomic bomb... also, I have the power, and can deliver it from batteries easily [high voltage is half of what I do]... and I know that they can be made flat and wide (a reason for thickness is the use of conductive glass that adds thickness, I plan to use a metal frame around the material so it does not get in the way)
also, regular polarized film works, when they are perpendicular, and the shutter is not activated, there is no light transmitted... but when it is activated, light goes though the first polarizer and then is rotated at a 90 degree shift in its wave so it may pass though the second... and also, what is this wide scale imaging you are referring to?... I plan to shoot single, small events like a soda bottle being chopped in half while full, or lit light bulbs smashing...

ADDITION: I just realized that I may have implied things like high speed as in for sports or the like, sorry if that was what it sounded like.

 

[AgX]

So, you have considered short duration flash and high-speed cameras already?

 

[knoxissimpler]

yes, and the short duration flash I have been using for quite a while now, but they have to be done in a darkroom since the shutter is left open.
and the high speed cameras are FAR too expensive to use... the crystal in the shutter (or liquid if kerr based) is the only thing I would have to buy, and it comes out to be far cheaper than a 10,000 dollar camera... and the casio ex-f1 is not out for a long time, and I like to use film, and it only has 1/1200 of a second refresh rate, not near fast enough for some things I intend to catch... (I plan to do, in the future, some bullets)

 

[Struan Gray]

The modulator I have came from Gsänger, now part of the Linos Group. You can see their range of modulators and pockels cells under optics on www.linos.com. Other manufacturers in the US market can be found in the useful Physics Today buyer's guide:

http://www.physicstoday.org/ptbg/resultsP.jsp?state=0&&country=0&&cat=1173

Your basic problem is that all these devices assume a particular path length through their active sections. If a ray traverses the device at a different angle it sees a different path length and it's polarisation is rotated by a different angle. It is no longer extinguished/passed in the same way as the straight-through ray, which at the very least gives you an inverted center-filter, and for wide apertures or wide angles of view the worst case means you either cannot block the light for all incident angles, or for all parts of the image.

So to use one as a shutter for a camera, you either have to build the optic system so that in some part of it all the rays are parallel as in an infinity conjugate microscope or in telecentric imaging, or you have to live with the fact that you can only see down a narrow tube - i.e. by using a long lens on a small format. The Rapatronic cameras used for U.S. Bomb tests were of the second type: they were a long way from their subject (several miles) and thus had the required narrow angle of view.

I don't know how fast you really want or need, but if you don't have the inclination or the budget for a digital high-speed camera (this is one area where digital sensors took over scientific imaging *very* early, which might be a clue your best bet would be to see if you could build your own rotating prism camera, or pick up a surplus one on eBay.

 

[knoxissimpler]

and there is your logical flaw: I am not using a modulator, which is designed only for lasers and optical transmissions, I am, however, using a shutter based off of the same principle. here is the tutorial I have for one that can be used as a camera shutter (and BTW, these have a response time in the nanoseconds, and theoretically the picoseconds) Dead Link Removed

here is a direct link to a diagram of its layout (it is easily compacted, the only reason I even made these posts was really for any other tuts like it or tips on use) Dead Link Removed

 

[Struan Gray]

That setup is working close to extinction and the Kerr cell is only rotating the polarisation of the light through a small angle. There can be a large percentage change in the light intensity, but the total 'filter factor' is very large.

To get more light through the system you need to rotate by a larger angle. That means higher voltages, or a thicker piece of crystal, or both. You can't go too high in voltage, so you end up with a thick piece of crystal. There is a reason the commercial versions are the size and shape they are.

Try it. I'd love for you to prove me wrong.

 

[tim_walls]

I'm finding this thread very confusing - you start by asking people for advice, but then respond by telling everyone they're wrong and you know more.

It all seems rather rude; or at least confusing at best.

 

[knoxissimpler]

that device rotates a full 90 degrees (which is all that is needed to allow light to pass through the second polarized filter), and I can go very high in voltages, I use 7,000 standard, and much of the time 50,000, and in the past have gone to 500,000, but the one linked to is NOT a kerr cell, but a pockels cell (kerr effect the energy is quadratic, pockels it is linear) and the crystal thickness does not matter, to a certain point, if the voltage and application of that voltage is proper (this is what modulators use, but the crystal is merely much wider, so that one does not need to be a good distance away) also, they are nowhere near extinction, just not as common for cameras... (that essentially is a modified light modulator that I linked to)... it allows a larger view...

ADDITION: @tim_walls: the point was for me to hopefully find more information, such as personal experience with one that was made for camera (not that laser stuff), or find another tut to compare mine with, I know what I plan to do works, I have most of the information, but I cant find anything such as someone who has used them, or exposure times (how many fractions of a second required), whether there is a better crystal to use that is more efficient, how much framing is best around the edges, etc etc