Effect of Bleaching on the Optical Band Width of theFCenter in KCl

Measurements have been made of the absorption in the $F$ region in KCl at 78°K. It has been found that the structure in this region is dependent on the presence of the $M$, $N$, $R$, and $K$ bands. The broadening in the presence of small amounts of $M$ absorption indicates that it is not simply due to the overlapping of $R$, $M$, and $N$ bands but is caused by an additional structure. These measurements support the present interpretation of the work of Van Doorn and Haven; they can explain the difference in the measurements of Pick and Geiger as well as the difference in the half-width observed by Mollwo and more recent data.