Laser spectroscopy of doubly excited9sns (11≦n≦20)and8dns (10≦n≦20)states of Ca

Doubly excited $ml=9s \mathrm{and} 8d$ states of Ca have been produced by multistep laser excitation via $4{\mathrm{sn}}^{\prime }s$ Rydberg states, and the states in which $n$ is from 20 down to $m+2\mathrm{}$ have clearly been observed by detecting photoionization current of ${\mathrm{Ca}}^{2+}$. In some states, remarkable interference patterns and considerable line narrowing caused by the interaction with other autoionizing Rydberg series have been observed. The quantum defects of the observed states have also been obtained and discussed. In addition, we have seen some resonance peaks which are likely to be interpreted as transitions to the states with $n=m+1\mathrm{}$ and $n=m$, although they have not definitely been assigned.