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Homemade strobe for high speed photography?

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GimpyJoe

Wed Feb 04 2009, 11:34PM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

Would it be feasible to build a HV flash to achieve fast flash durations? I've been reading up on high speed photography and have looked at a lot of the DIY sites on the subject, and everybody seems to use commercially available flash units with slow electrolytic capacitors.
I was thinking of buying a high-power xenon flash tube (

) and powering it with a homemade hv capacitor and spark gap to get an extremely short pulse.

Would this work? I suspect I'm missing something here, because if it was this easy someone on this board would have done it by now.

...

Wed Feb 04 2009, 11:53PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

How fast of a flash are you looking for? Regardless of how fast a pulse you try to run in a xenon bulb you will always have a few hundred us (IIRC) pulse, just from the gas itself 'cooling' off. The next step up is using an arc just in open air, there was an article about such issues on the forum somewhere (it may have been on old.4hv.org, search should turn it up), or a tube specifically designed for high speed discharges (good luck finding one, I would try ebay)

Another thing I have been wanting someone to try is using an laser (q-switched yag would probably be your best bet, ex a ssy-1 laser) instead of just a strait flashtube. Your main issue would be that there is a relatively limited amount of energy (only some hundredths of a joule), but you will get an extremely fast pulse (on the order of several us down into the tens of fs depending on the laser) and it would be well colminated. With careful planning to make sure that the target is fully covered by the beam and a decently sensitive camera I would expect it to work very well, allowing you to capture just about all imaginable events.

for example, even with a 'long' pulse of 1us, an object moving at the speed of light would only travel about 3m

Proud Mary

Thu Feb 05 2009, 12:08AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

If you google "high speed spark photography" you'll find things that will interest you.

rp181

Thu Feb 05 2009, 12:22AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

I would love to try laser's, but i don't have a laser =p
Having a high intensity light is pointless unless its a very fast event, so shorter pulse. What is intended application?

Myke

Thu Feb 05 2009, 01:21AM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

...For high speed photography.

It would seem like LEDs would be pretty fast. They also can be really bright too. I am not exactly sure about the speeds but they should be faster than a xenon flash tube (on the turn off).

Hon1nbo

Thu Feb 05 2009, 02:40AM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

build a flash bomb based on Argon and using an exploding wire... I have been meaning to try this, but I still have to put together a Cap bank that will set it off (so I don't have to use any explosives)...
the basic design is a tube with one transparent end filled with low pressure Argon gas that is rapidly raised in pressure via a small explosion (for safety and legallity, I planned to try an exploding seed wire in an "L" shaped tube so that the light produced by the current flowing through the wire, which lasts longer than the desired light, would not come through... though maybe it would still be fast enough given proper design and a low value high voltage system? (approx. speed is in the single microsecond range IIRC)

Possible you could built a Kerr or Pockel Cell and have it pulse a high slow, but intensity light (or even better, your shutter) - this is another thing I have wanted to build but the main issue is the medium used for the Kerr/Pockel effect to take place (with Kerr, the liquids that use lower energies to be practical are highly toxic compounds such as Nitrobenzene, or in the case of pockel cells while the energy is lower, the crystals used can be expensive if you do not have a good source - I actually thought about growing mine and having them ready for when I go to college ^_^) - pulse ranges are fast enough to catch a still image of an Atomic Bomb, before the bomb tower has been fully engulfed in flames (measured speed is around a few nanoseconds)

oh, and unless you are using Black and White film, with lasers you would get a single colored scene (which may not be good for your subjects) unless you were good at color mixing lasers or used supercontinuum light.

rp181

Thu Feb 05 2009, 03:27AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

by intended use, i meant the actual object that is being photograph. The Speed is a big factor.

likewhat

Fri Feb 06 2009, 04:44PM

Account deactivated by user request on 6/11/2009.
Registered Member #1071 Joined: Fri Oct 19 2007, 02:13AM
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Posts: 44

I have used a laser to take pictures of plasmas. In general you need something that is qswitched because in a short pulse (a few ns or less) you need a pretty high power to have enough light to take a picture. A good thing about using a laser is you can use a filter to let only the laser light through so if you are taking a picture of a bright plasma you dont saturate the camera with self emission from the plasma.

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