Coincidence spectroscopy of high-lying Rydberg states produced in strong laser fields

We report on the measurement of electron emission after the interaction of strong laser pulses with atoms and molecules. These electrons originate from high-lying Rydberg states with quantum numbers up to $n \lesssim 120$ formed by frustrated field ionization. Simulations show that both tunneling ionization by a weak dc field and photoionization by the black-body radiation contribute to delayed electron emission on the nano- to microsecond scale. We measured ionization rates from these Rydberg states by coincidence spectroscopy. Further, the dependence of the Rydberg-state production on the ellipticity of the driving laser field proves that such high-lying Rydberg states are populated through electron recapture. The present experiment provides detailed quantitative information on Rydberg production by frustrated field ionization.