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Instrument design -- deliver specific amounts of energy to a 50mm diameter circle

  1. May 19, 2016 #1
    I didn't know where to put this, I figured I'd start here since this area sees traffic that other areas might not see. Someone can move it if there's a better section for it.

    I'm thinking of an instrument design that has a light path as follows: UV-Vis light source, monochromator or filter that allows only a particular wavelength through, some tubes or whatever, and then the system needs to apply the light to at most the area of a 50mm circle. And, I need a shutter somewhere in that light path, but not an open/closed one. I need one like a camera shutter where I can use a computer or something to tell it to be opened for a specific amount of time so that if I know the output of the lamp in W/m2 I can apply a particular amount of energy per square meter depending on how long the shutter is open. The time it's opened will depend on the source but I'm looking to expose the sample to usually around 0-10J/m2 and possibly more but that's easy, it just stays open longer and usually faster shutter speeds are harder to achieve. I'm having trouble finding such a part, does anyone know of one? This isn't for a spectroscopy application.

    So basically I need a machine that can precisely and accurately deliver specific amounts of energy to a 50mm diameter circle. I've been using a DNA crosslinker but the lamp stability is dicey if the time the lamps are on is shorter than 30sec, which is pretty much all my exposures.
  2. jcsd
  3. May 20, 2016 #2


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  4. May 20, 2016 #3


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    This sounds sort of like how any typical, modern camera works (any camera with automatic exposure capabilities, which is pretty much most of them since the last half century).

    Have you considered getting a medium format film SLR camera (6x6 cm format should work nicely) -- one with interchangeable lenses so that you can simply detach the lens (sounds like you don't need a lens) -- and placing your 50 mm circle where the film plane would normally reside? The light meter and shutter control should still work in this setup.
  5. May 20, 2016 #4
    I actually used to shoot with a bronica but I don't have it anymore. That's certainly an interesting idea and I bet it would work, the poor camera would be getting hit with 255nm light a lot though. Those shutter parts are nice as well. It's nice to know my options, but I'm beginning to think they're moot points because I don't think the PI is going to approve of this build since I don't actually have any parts yet and it will cost a fair amount of money.

    I think I'm going to try just 3D printing a cylinder that hold the dish on the inside and then a neutral density filter on top and placing that in the crosslinker so that it reduces the amount of light hitting the dish. Since I have a lightmeter I can put the filter over the meter and measure the new irradiance when the lamp is stable and then calculate the time I need to enter into the machine to make it deliver a particular amount of energy. Plus I know the transmission of the filter so I can see how much light should theoretically reach sample.

    Thanks for the help though, much appreciated!
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