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Thomson optical depth

(a measure of affects of Thomson scattering)

The Thomson optical depth is optical depth due to Thomson scattering and is of interest when the latter is the primary type of scattering, e.g., when electromagnetic radiation (EMR) passes through a medium in which it is likely to pass close to electrons, i.e., an ionized medium. Determining the Thomson optical depth is of interest in studying distant EMR such as the cosmic microwave background, that passed for a long distance through reionized media, since the opaqueness due to Thomson scattering produces tends to cover up interesting detail in the primordial CMB such as deviations and polarization.