Magneto-Optic Experiments on theFCenter andACenter in KCl

Abstract

We report the measurement of the magnetically induced circular dichroism in the optical-absorption bands of the $F$ center and $A$ center in KCl performed to test theoretical productions of Henry, Schnatterly, and Slichter based on the method of moments. It is found that a magnetic field can alter the area of an optical-absorption band, but only at the expense of other optical-absorption bands of the center; the total area due to all the optical-absorption bands of the center remains constant. The magnetic field causes the $F$ band to shift in energy. The shift is found to be greater in the peak than in the tails of the $F$ band. Depending upon the orientations of the $A$ centers, the magnetic field causes either a shift in the $A2\mathrm{}$ band, or an increase in the area of the $A2\mathrm{}$ band and equal and opposite decrease in the area of the $A1\mathrm{}$ band. These results are in good agreement with the predictions of Henry, Schnatterly, and Slichter. We show that the signals from paramagnetic circular dichroism in the $K$ band and $F$ band occur with the same spin-lattice relaxation time, confirming that the $K$ band is an excited state of the $F$ center. The ratios of the coupling to the cubic and noncubic lattice modes of the $F$ center and the ratios of the spin-orbit coupling constants of the $A$ center are also evaluated.