Very high Rydberg states and external fields

Excimers are very important to laser physicists since they possess no stable ground state, they may emit radiation but are incapable of reabsorbing it. They are therefore fully transparent to the radiation which they can produce and, since they also are naturally formed in a condition of population inversion, provide an excellent laser medium. 

28 Very high Rydberg states and external fields 

15 Strictly speaking, the word is inappropriate, since it comes from excited dimer and the molecules described are heteronuclear. Various other names have been proposed, but the common usage is followed here. 

However, in experiments on electron attachment from very high Rydberg states, in which a specially designed cubic cage was used, Stark components were minimised in order to adjust the voltages on the box and thereby compensate external electric fields to a precision of 5 /zV per mm. Thus, Rydberg states of n 1000 have been observed [80, 81], which is higher than any astrophysical value yet reported thus, it is very important to achieve precise cancellation of external electric fields. 

If we turn this requirement around, it is clear that high Rydberg states themselves may be used as excellent probes to reveal the influence of external fields on quantum systems. In fact, Rydberg atoms are widely used to probe the influence of either static electric and magnetic or AC fields, or combinations of fields. Examples of how the influence of external fields can be studied will be presented in chapters 9 and 10. 

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