Comparing Microwaves and visible light,
1 Microwaves see generally rough surfaces as smooth ones
2 For polarizing microwaves wire polarizers are enough whereas for visible light we need aligned polymers or crystals.
1. The amount of scattered light strongly depends on the wavelength. For example Rayleigh scattering grows with the fourth power of the inverse wavelength or frequency. This is btw the reason why the sky is blue.
2. For polarizers, the distance between the wires has to be of the order of the wavelength.
@ Mr. Ingo,
Scattering analogy gave me good initial idea about the apparent surface roughness.
Coming to the polarizers...
It seems to me that the grids in the polaroid film lead to diffraction of light passing through it. Hence microwave rays incident on normal polaroid films must give a significant diffraction patterns after passing through the film which requires the polaroid or polarizer grid to have larger separation.
But still I am not convinced with the fact that a wire grid polarizer used for Microwaves can polarize all the light passing through it.
Doesn't the Microwave rays pass through the void between the wires uninterrupted?
The answer you can find in the “classical” paper by H.E.Bennett and J.O.Porteus, published in Journal of the Optical Society of America, 1961, vol. 51, #2, pp. 123-129.
The important condition for independence of roughness at different wavelength is indicated there: The distribution of heights of the surface irregularities should be Gaussian about the mean value. If the apparent roughness is different for different wavelengths, it means that the surface irregularities are not in agreement with this requirement.
Best,
Vladimir Voitsenya
Roughness is dependent on wavelength as scattering/diffraction depends on size of scatter relative to wavelength of light e.g in optical region also when size of diffracting aperture becomes of sub-wavelength order one gets only single beam of light instead of different orders. Further decreasing the size results in specular reflection.
In case of polarization size or in fact separation between wires should not be very large so that electromagnet field (light or other) of the incident wave cannot interact with the wires. This is dependent on wavelength of the em wave. In case of microwaves wavelength is larger than light and thus light polarisers are made with polymers or crystals where spacing in atoms is small.
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