Hamburg 2009 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 34: Poster II
A 34.46: Poster
Donnerstag, 5. März 2009, 16:30–19:00, VMP 9 Poster
Multiphoton Ionization of Lithium — •Michael Schuricke1, Jochen Steinmann1, Ganjun Zhu1, Igor Ivanov2, Anatoli Kheifets2, Alexander Dorn1, and Joachim Ullrich1 — 1Max Planck Institut für Kernphysik, Heidelberg, Germany — 2Australian National University, Canberra, Australia
For the first time a systematic study on multiphoton ionization (MPI) of atomic lithium by near-infrared fs-laser pulses has been conducted in both, experiment and theory. Due to its low ionization energy lithium shows a qualitatively different behavior compared to the widely studied noble gases.
The classical over-the-barrier intensity where the electron is essentially field ionized
is attained for a Keldysh parameter of roughly 5, i.e. deep within the MPI domain.
Thus, lithium provides an excellent target to observe a direct transition from MPI to over-the-barrier ionization (OBI).
In the experiment Ti:Sa laser pulses of 30 fs duration and λcentral=775 nm
were focused onto an ultra-cold sample (T = 1 mK) of lithium to reach peak intensities between 1011 and 1014 W/cm2. In the calculation the lithium atom is described in the frozen-core Hartree-Fock approximation in order to solve the time-dependent Schrödinger equation on a grid.
To improve the comparability of experiment and theory several calculated spectra were averaged, weighted with the peak intensity distribution present in the experiment.
Both, experimental and theoretical calculations suggest that the transition from MPI to OBI manifests itself in an increasing contribution of parity forbidden partial waves in the continuum wavefunctions.