Turn a filter; then add a phase delay
A silent ideal monochromatic model. Percentages are relative to light after the first ideal polarizer. No colors or stress values are inferred.
Wavelength fixed at 550 nm. Analyzer stays crossed at 90°.
What this can and cannot explain
No sample: I/I₀=cos²α. Crossed polarizers with an ideal uniform retarder: I/I₀=sin²(2θ)sin²(πΔ / λ). θ is the sample-axis angle to the first polarizer; Δ is optical path difference. This is not a stress reconstruction. Thickness, material coefficient, stress geometry and wavelength dependence are omitted. A white-light photograph cannot be reduced to this single-wavelength bar.
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