Abstract
The optical absorption of M centers in potassium chloride crystals has been studied by observing the anisotropy induced in the crystals after bleaching with polarized light. It is found that the M center has absorption bands hidden under the F band in addition to an absorption in the 800-mμ region. The observed anisotropy near the F band is the result of the presence of other absorption bands in the F-band region. The optical absorptions of R and N centers have also been studied. The change in the location and half-width of the F band during bleaching can be accounted for by the presence of secondary centers.