Measurement of irradiance of 2 beam interference

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Discussion Overview

The discussion revolves around measuring the amplitude of irradiance in a two beam interference experiment. Participants explore methods for utilizing a power meter and a CMOS camera to achieve accurate measurements.

Discussion Character

  • Experimental/applied, Technical explanation

Main Points Raised

  • One participant inquires about measuring the actual amplitude of irradiance using a power meter and a CMOS camera.
  • Another participant suggests that the camera's RGB values may not be linear due to potential gamma processing and recommends calibrating the CMOS sensor against the power meter.
  • A calibration method is proposed, involving adjusting light levels and recording RGB values to create a lookup table for converting camera values to relative illuminance.
  • A later reply confirms the creation of a lookup table and the determination of an average calibration factor for a specific exposure time.
  • There is a follow-up question regarding the linearity of the calibration curve and a reminder to ensure the camera is set to manual mode to avoid automatic adjustments.

Areas of Agreement / Disagreement

Participants appear to agree on the general approach of calibrating the camera against the power meter, but there is no explicit consensus on the linearity of the calibration curve or the effectiveness of the camera settings.

Contextual Notes

There are potential limitations regarding the linearity of the camera's response and the accuracy of the calibration process, which are not fully resolved in the discussion.

Who May Find This Useful

Researchers or students involved in experimental physics, particularly those working with optical measurements and interference patterns.

ppoonamk
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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
 
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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.
 
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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
 
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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