Coherent Control of Atomic Ionization by Two-Color Laser Fields

L. FECHNER; N. CAMUS; S. NAGELE; C. LEMELL; S. D. LÓPEZ; T. PFEIFER; R. MOSHAMMER; D. G. ARBÓ; J. ULLRICH; J. BURGDÖRFER

Frankfurt

Conferencia; 12th Eurepean Conference on Atoms, Molecules, and Photons; 2016

Goethe Universität

Strong-field ionization of atoms with near infra-red laser pulses reveals a rich structure in the momentum distribution of the liberated electron. The patterns observed (Fig. 1) arise from the interferences of multiple pathways leading to the same final momentum state. They retain precise information about the creation of electron wavepackets in the laser field and the phase they accumulate during the propagation in the combined laser and ionic Coulomb field [1].We present experimental results and a theoretical analysis of the ionization process of argon interacting with linearly polarized two-color fields. These laser pulses are formed by the combination of 800 nm laser pulses and their frequency-doubled component (400 nm). By controlling the relative phase between the red and blue carrier waves, we can control the ionization rate via the temporally modified electric field strength. More importantly, this shaped field controls also the trajectories of the ionized electron and the accumulated phase leading to modified interference structures in the 3-dimensional momentum distributions. We precisely monitor the modifications of the interference structures.Electron momentum distributions are recorded with a reaction microscope. The results are compared to simulated spectra that were obtained by using strong-field and Coulomb-Volkov approximations as well as ab-initio solutions of the Time Dependent Schr¨odinger Equation (TDSE). The comparison enables us to determine the influence of the ionic Coulomb potential on the ejected electron. In addition, this allows for characterization of unknown experimental parameters such as the absolute value of the relative two-color phase f. We also performa study of classical-quantum correspondence in the simulation of laser-atom interactions. We find a surprisingly good agreement between Classical Trajectory Monte Carlo (CTMC) analysis and TDSE simulations which might open the pathway for an improved understanding of previously unexplained features observed in experimental spectra.[1] Diego G Arbó, Shuhei Yoshida, Emil Persson, Konstantinos I. Dimitriou and Joachim Burgdörfer, Interference Oscillations in the Angular Distribution of Laser-Ionized Electrons near Ionization Threshold, Phys. Rev. Lett. 96, 143003 (2006).[2] Diego G. Arbó, Christoph Lemell, Stefan Nagele, Nicolas Camus, Lutz Fechner, Andreas Krupp, Thomas Pfeifer, Sebastian D. López, Robert Moshammer and Joachim Burgd¨orfer, Ionization of argon by two-color laser pulses with coherent phase control, Phys. Rev. A 92, 023402 (2015).