Studies of Metastable Levels in Singly Charged Ions by Laser Techniques in an Ion Storage Ring

Abstract

Experimental techniques have been developed at the ion storage ring CRYRING in Stockholm for measurements of lifetimes of metastable states. The methods are based on laser techniques and utilize the qualities of fast ion beam laser spectroscopy (FIBLAS). With these laser techniques we have been able to measure lifetimes in a range from 3 ms to 5 s. The lower limit is set by the injection time for ions into the ring, while the upper limit is related to the time for which ion storage could be achieved in the ring. One advantage of the present method is that collinear laser excitation gives high spectral resolution and consequently high selectivity. Even hyperfine selective measurements are possible. By laser probing, the detection efficiency can be very high although the forbidden decay processes are extremely weak. The methods have been applied to the nd2DJ levels in Ca+ and Sr+ and have been shown to be competitive to ion trap measurements. More recently, measurements have been performed on metastable levels in Fe+ and in the rare earth elements Eu+ and La+. The latter measurements take advantage of the attractive properties of the technique and are the first experimental studies of forbidden decay rates in these elements. The techniques are described and results presented.