Optical absorption in MgO: Cr3+

Experimental measurements of the absorption cross sections of the sharp A24→E2 transitions in triply charged chromium ions in MgO are described. The measured R-line absorption strength per ion is in good agreement with the value calculated by Macfarlane. Values for the absorption strengths of the N lines are obtained and are shown to be consistent with what is known from fluorescence studies about the dipole nature of these transitions. Some sharp lines are seen in absorption which do not appear in fluorescence and the possibility that these are caused by transitions originating on chromium ions in rhombic sites is discussed.