A question about circularly polarized light


At work, a senior colleague thinks that circularly polarized light does not exist. My problem is that we both work on a project involving polarized light. In some occasions, I would like to point out some artifacts that I can identify in the circularly polarized component (because I am computing the Stokes parameter that describes exactly that). My colleague insists to dismiss those arguments of mine on the basis that circularly polarized light does not exist. Instead, he argues, I should measure linear polarized states, and reason from there.

How can I show that circularly polarized light actually exists, and as a pure state? Or am I wrong?

My line of reasoning is that transversal waves are solutions of the wave equation. As this equation is linear, a linear combination of solutions is also a solution. And in that linear combination, I'm free to use complex coefficients. Hence, circularly polarized light is perfectly possible as an inherent property of light.

Now it turns out that my colleague is not particularly well versed in math, so my line of reasoning does not fly a single nanometer. Besides, it would be advantageous to me if I can also get someone else on my side, specially on the management floor, and math is certainly not the way.

I've read that there exist chiral molecules, which modify circularly polarized light, but do not affect linear polarized light. Some sugars, and also some oil-derivatives. But I could not find an explanation of the effect, much less an intuitive one.

My colleague knows the effect of a QWP very well, but, he still thinks that circularly polarized light is a mental construction. More or less like some statistical blah-blah from the newspaper, that one is advised not to trust, unless one really knows what is going on. When I speak of Stokes parameters, he tends to mistrust the thing. I personally find math arguments very helpful to stay on safe ground, but it is also very difficult to communicate that feeling of safety to others. The guy is neither stupid nor obtuse, by any stretch of those concepts. In a way, I find it sane that he asks for arguments.

Best Answer

With two circular and one linear polarisers you can do it. Use an unpolarised light source. First show that half the light passes the two circular polarisers when aligned and none passes when they are anti-aligned. So there is polarisation. Then replace the second filter by the linear filter and show its orientation does not matter. So the polarisation is not linear.

If that does not help, repeat the experiment by Richard Beth in 1935. Or get your colleague fired.

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