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Earth and Space Sciences · 术语表

什么是 Extinction position, extinction angle？

又称： extinction position · extinction angle

Definition 8.11 University Earth and Space Sciences — Year 1 · 第 8 章 — Optical Mineralogy

An anisotropic grain between crossed polars is in an extinction position when it is dark because its vibration directions are parallel to the polariser and the analyser. The extinction angle of a grain is the angle between a direction visible in it (a cleavage trace, an elongation, a twin plane) and the nearest extinction position, read on the graduated stage.

$The intensity passed by a grain as the stage turns, at the wavelength 550\, nm, for three retardations (). Four extinctions per turn, four maxima at 45 from them; the retardation sets the height of the maxima, which is nearly zero when is close to a whole number of wavelengths.$

The intensity passed by a grain as the stage turns, at the wavelength

550\,\mathrm{nm}

, for three retardations (Theorem 8.10). Four extinctions per turn, four maxima at

45{}^{\circ}

from them; the retardation sets the height of the maxima, which is nearly zero when

\Delta

is close to a whole number of wavelengths.

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