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Measurement of irradiance of 2 beam interference

  1. Oct 1, 2014 #1
    Hi,

    I have an experiment set up to get two beam interference fringes. I would like to know how I could measure the actual amplitude of the irradiance from the experiment. I have with me a power meter and a CMOS camera. How can I go about this? Thank you
     
  2. jcsd
  3. Oct 2, 2014 #2

    sophiecentaur

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    Your Camera Sensor will provide you with RGB values for each pixel. The response of the camera may not be linear - there may be a 'gamma' involved in the processing. If your power meter measures incident optical power, you could calibrate the CMOS sensor against it, to linearise the light / pixel value law. You would adjust the light level (neutral filter or iris) to vary the irradiance in a linear fashion with the power meter and look at the RGB (Y) values from the sensor. Of course, you would need to use a manual setting for the camera exposure and find a suitable range of values so that you get the 1 -256 values. A bit fiddly but quite doable with care, imo. You can then make a lookup table to convert camera values to relative illuminance.
     
  4. Oct 7, 2014 #3
    Hi,

    Thank you for your idea. I made a lookup table to convert it to power readings and found the average calibration factor for a specific exposure time. Thank you so much for the help
     
  5. Oct 8, 2014 #4

    sophiecentaur

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    I'm pleased that it's helped you with a solution. Digital cameras can be a brilliant 'free' piece of lab equipment.
    BTY, is your calibration curve near a straight line? Are you sure you are set to Manual - cameras can be too damned smart sometimes?
     
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