Yield curve fitting elimination

The collisional preexcitation has the drawback, that several levels are simultaneously excited, which may feed by cascading fluorescence transitions the level k) whose lifetime is to be measured. These cascades alter the time profile IpL(t) of the level i> and falsify the real lifetime rj (Fig. 11.41b). This problem can be solved by a special measurement cycle For each position x the fluorescence is measured alternately with and without laser excitation (Fig. 11.41c). The difference of both counting rates yields the LIF without cascade contributions. In order to eliminate fluctuations of the laser intensity or the ion-beam intensity a second detector is installed at the fixed position Xq (Fig. 11.42). The normalized ratios S(x)/S(xq) are then fed into a computer which fits them to a theoretical decay curve [11.104]. 

---