The theory of the transmittance of a train of three dichroic linear polarizers is described. The incident light is supposed to be unpolarized and the first and third polarizers to have parallel orientations. A train of three polarizers differs from a train of two polarizers in that the birefringence of the middle polarizer enters importantly into the result. A very surprising fact is that the transmittance of the train does not always have its minimum value when the middle polarizer is crossed with the other two. If the cosine of the relative phase retardation of the middle polarizer lies between zero and minus one, the transmittance has a relative maximum at the crossed position and the minimum occurs at an orientation which, in the numerical case discussed in Part 6, is 18.5° either way from the crossed position. It is shown in Part 6 that this surprising result has an elementary quantitative explanation.
The general expression for the transmittance of three (not necessarily identical) linear dichroic polarizers is given in Part 4, and various special cases are given in Parts 5 through 10. The simplest case that reveals the interesting behavior just described is that in which the two outside polarizers are ideal and this is discussed in Part 6.
© 1956 Optical Society of AmericaFull Article | PDF Article
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