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Thread: extending the range of my laser power meter

  1. #1
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    Default extending the range of my laser power meter

    a while back I wanted to up the power my meter can read it tops at 40mw and some people had mention wedge type prisms to act like a beam spittle
    but I can fond the original threat, my question to that is what angle should the wedge side have?
    I was also thinking of adding resistors to the sensor to lessen it's output, I guess for quick measurements that would work but still not exactly sure.
    thanks for any info you guys may have
    I now have a class for green as well so a filter for the sensor or a wedge may be the way to go? or adding like a divide by 2-10 times would may work as well, I have a higher power meter on loan so I have a reference to use, the beam splitters I have tried sis not have a repeatable or predictable result for some reason
    Remember Remember The 8th of November, When No One Stood, but Kneel, In Surrender
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  2. #2
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    What type of LPM are you referring to ?? Optical or Thermal ??
    A resistor in series with any sensor would definitely un-calibrate
    a calibrated sensor
    You could use a Neutral Density (ND) Filter buy you would need
    test the Power Reduction ratio at the specific wavelength of your
    Laser under test. The same ND filter does not necessarily have
    the same Power Reduction ratio at different wavelengths..

    At.. for example a 10 x reduction your reading resolution will
    drop 10 fold.


    Jerry
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    ... you can stack several filters to add the reduction (virtually limitless) - but, as Jerry says, you have to measure the "reduction" of one (or a fixed number of) filter(s) for every wavelength to get correct numbers ...

    Viktor

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    Google Hershel wedge
    "There are painters who transform the sun into a yellow spot, but there are others who, with the help of their art and their intelligence, transform a yellow spot into the sun." Pablo Picasso

  5. #5
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    sorry for the late reply but the meter I have is an optical type
    http://www.ebay.com/itm/Sper-Scienti...0AAOSwaApZkH-g

    it's mot linier but comes with a correction table,

    Now for a wedge prism what should the angle of incidence be? I have seen a few that have different slopes if you will
    Remember Remember The 8th of November, When No One Stood, but Kneel, In Surrender
    In a popular government when the laws have ceased to be executed, as this can come only from the corruption of the republic, the state is already lost. Montesquieu

  6. #6
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    Companies that sell good wedges know what the index of refraction is for the glass they use. With that and the wedge angle, you can calculate the Fresnel reflectance for the wedge. I would imagine something 20 degrees or less is a good start.

    Steve
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  7. #7
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    I ended up finding 3 fairly liner beam splitters that have an AOI of 20 degrees, I found them on ebay brand new from a local seller sold me 3 for 14 bucks I think, if I need more reduction I can cut them in half as they are long enough, optically they look like neutral density filters but at 20 degrees one cuts 50%
    Remember Remember The 8th of November, When No One Stood, but Kneel, In Surrender
    In a popular government when the laws have ceased to be executed, as this can come only from the corruption of the republic, the state is already lost. Montesquieu

  8. #8
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    Why not just use nd filters

  9. #9
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    they cost more, lol
    Remember Remember The 8th of November, When No One Stood, but Kneel, In Surrender
    In a popular government when the laws have ceased to be executed, as this can come only from the corruption of the republic, the state is already lost. Montesquieu

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