I am kind of new to laser physics and signal processing, I hope I am in the right place to ask this question. I am also sorry for my not-great English.
I have been asked to study the transverse intensity profile of a laser beam produced by a $\rm He$-$\rm Ne$ source using a commercial webcam. I am placing the webcam sensor (without any lens) in front of the source and taking a snapshot. Then I am assigning each pixel an intensity value that is simply the recorded value in the red channel ($0-255$). If I choose a row of pixels and plot such value as a function of the pixel, I should expect a Gaussian profile. However it is not what I am observing.
In red you can see a Gaussian fit of the data. The actual data is shown in blue. I cannot really call this a good Gaussian shape, although it is some kind of a bell.
- What could cause such a shape?
- Could it be due to the laser source which could not be perfectly single-mode?
- Or could it be due to the sensor?
It is interesting to note that I have also produced an image after making the beam pass through a single mode optical fiber, obtaining similar results; this makes me think that the problem lies in the sensor. However, the only modification the sensor causes and that I am aware of is Gamma correction, and as far as I know, that means that the red (or any channel) value is elevated to a power which is usually $<1$, but that should not change the actual shape. A Gaussian function elevated to a power is still a Gaussian function, although its parameters are different. Can anyone help?