Single and double ionization of magnesium via four-photon excitation of the 3 p2 1S0 autoionizing state: Experimental and theoretical analysis
Abstract
Single and double ionization of ground state Mg atoms is observed in an atomic beam experiment in the 584-596nm spectral range with a maximum intensity of 9×1011W/cm2 and pulses of ns duration. The Mg+ spectrum consists of a single broad resonance whose position is very sensitive to laser intensity and it is attributed to the four-photon excitation of the doubly excited 3p2S01 state. For intensities higher than 2×1011W/cm2 a considerable double ionization yield is obtained. The Mg2+ spectra are composed of two lobes, each one dominating at different intensities. These observations can be interpreted by a sequential mechanism in which doubly charged ions are created by multiphoton resonant ionization of the excited 3p1/2,3/2 Mg+ states (with negligible contribution from the 3s1/2 ionic ground state) after the single ion production has saturated. The population of these excited ionic states suggests the absorption of two photons above the first ionization threshold of Mg . This interpretation is unambiguously confirmed by a complementary fluorescence experiment. Moreover, both ionization and fluorescence spectra as well as ionization yields are very well reproduced by a theoretical model based on a combination of density matrix and rate equations, taking into account the near-resonant coupling between the 3p2S01 and 3p3dP11 autoionizing states and employing calculated parameters for both Mg and Mg+ . It is thus pointed out that for visible ns pulses of moderate intensity the autoionizing resonances play a crucial role in the multiphoton sequential double ionization of alkaline-earth-metal atoms.
- Publication:
-
Physical Review A
- Pub Date:
- September 2004
- DOI:
- 10.1103/PhysRevA.70.033403
- Bibcode:
- 2004PhRvA..70c3403L
- Keywords:
-
- 32.80.Rm;
- 32.80.Dz;
- 33.80.Rv;
- Multiphoton ionization and excitation to highly excited states;
- Autoionization;
- Multiphoton ionization and excitation to highly excited states