I'm sorry to be pedantic folks, but I wince each time I see this repeated in
the digest:
"An circular polarizer has an second layer, which depolarize, "scramble"
the polarisation of the light. "
Light from the scene consists of all possible orientations of the electric (or
magnetic) field vector. A linear polariser selects only those of a certain
orientation. Take a look at a TV antenna, you will see the dipoles are oriented
either horizonatally or vertically. This for exactly the same reason.
Now, a linearly polarised photon is actually a mixture of two circularly
polarised photons (left and right handed). The electric (or magnetic) field
vector is not oscillating in a plane as for a linear photon, but is rotating
either clockwise or anticlockwise.
The circular polariser selects one 'handedness' type of photon rather than the
other.
Strictly speaking 'depolarisation' would be the process of taking linearly
polarised light and introducing a variety of phase shifts so that the light was
no longer polarised, but a mixture of all polarisations.
Chris Barrett
Malvern UK
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