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Prism for separating UV

  1. Nov 2, 2013 #1
    Hi,
    I am working on my thesis which is going to be uv instrumentation using photodiodes.

    I had in mind to extract the UV from the whole solar spectrum at sea level. I know that the UV band is narrow compared to visible and IR. I also wish to experiment with the various components like UVA, UVB and UVC which are part of the solar spectrum.

    What type of prism do you recommend? size, material etc..

    Also I would like to conserve the intensity of the radiation.

    thanks
     
  2. jcsd
  3. Nov 2, 2013 #2

    Vanadium 50

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    Glass tends to attenuate UV, and the attenuation is strongly wavelength dependent. Can you use diffraction instead?
     
  4. Nov 2, 2013 #3
    the attenuation will be greatly lowered if you use UV A radiation. What wavelengths are you using?
     
  5. Nov 2, 2013 #4

    Vanadium 50

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    Read his message:

     
  6. Nov 2, 2013 #5

    mfb

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    Fused quartz transmits UV radiation (at least the part coming from the sun).
    Larger is better, but more expensive.

    Narrow in which way?
     
  7. Nov 2, 2013 #6

    Vanadium 50

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    Quartz is unquestionably better than glass, and it has a nice dispersion in refractive index vs. radiation wavelength. However, it still attenuates in a frequency dependent manner. (You have the same problem with going to even more exotic materials like fluorite.) That's why I suggested diffraction.

    If you go with refraction, there will need to be some calibration to remove this effect.
     
    Last edited: Nov 3, 2013
  8. Nov 2, 2013 #7

    ZapperZ

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    That last part is almost impossible to be done with a prism because it WILL attenuates. Not only that, depending on the transmission/absorption profile, it will attenuates each wavelength differently. So not only will you not conserve the intensity, you won't get them in the same proportion to each other after the prism.

    Using a spectrometer with some sort of a diffraction grating might be the best way to go, as V50 suggested. That is what is commonly used at synchrotron light sources to extract the light from the electron beam passing through an insertion device.

    Zz.
     
  9. Nov 3, 2013 #8
    I will go for diffraction. What type of diffraction do you think is best for one photodiode?

    I will try to design the optical stage to get the best signal to noise ratio from the photodiode to get the best measurements. Regarding the photodiode, i will either use one sensitive to uv or else one with normal response with a diffuser.

    I assume the diffraction formula with sin teta, wavelength and distance, will help me position my photodiode
     
  10. Nov 4, 2013 #9

    Andy Resnick

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    AFAIK, the instrumentation used in UV spectroscopy is largely the same as visible- I have a small spectrometer (Stellarnet) that operates from 200-900 nm using a single grating and line detector. In fact, Stellarnet and Ocean Optics both make spectrometers specifically designed for field measurements- why are you reinventing existing products?
     
  11. Dec 10, 2013 #10
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