Time-dependent dynamics of atoms and molecules probed by short laser pulses - Attosecond Physics.

In recent years, the possibility of producing and applying hyper-short pulses, in the range from a few decades of femtoseconds down to the attosecond regime, has created new challenges to theoretical atomic and molecular physics as regards the computation and interpretation from first principles of time-dependent processes induced from the interaction of hyper-short pulses with atomic or moecular states.
Of special interest in this area are the topics of coherent excitation and decay of highly excited states, or of phenomena due to various pump-probe schemes, including two-color IR+XUV spectroscopies such as attosecond 'streaking' [1]. In order to explore quantitatively the corresponding physics for real atoms, it is necessary to solve reliably the time-dependent Schrodinger equation (TDSE) in a framework where the many-electron problem resulting from interelectronic interactions is taken into account.
In view of the above, our recent and current activities have focused on the development and implementation of polyelectronic time-dependent computational methods in first-order or in all-orders of time-dependent perturbation theory for the ab initio treatment of a variety of time-dependent phenomena. As regards the nonperturbative methodology, which includes explicitly the participation and contributions of the discrete as well of the continuous specta, this is based on the 'State-specific expansion approach' (SSEA) [2], which solves the TDSE by expressing the solution, Ø(t), in terms of the state-specific wavefunctions of the physically and computationally relevant energy regions:

SSEA
Characteristic recent applications of our work can be found in [3-5].
For example, the figure below shows the integrated, over the energy å' of the å'p scattering orbital, probability distribution of the å'p continuum states as a function of energy å and of time t. The ground state ^{2}P^{0 }interacts with a trapezoidal laser pulse of duration 450 a.u. (10.9 fs), frequency ù= 4.851 a.u. (132 eV) and intensity 8.75x 10^{11} W/cm^{2}. The Auger energy distribution exhibits a Fano-type asymmetry with peak values at 31.7 eV.

References

[1] F. Krausz and M. Ivanov, 'Attosecond physics', Rev. Mod. Phys. 81, 163 (2009).
[2] Th. Mercouris, Y. Komninos, S. Dionissopoulou and C. A. Nicolaides, 'Computation of strong-field multiphoton processes in polyelectronic atoms. State-specific method and application to H and Li-', Phys. Rev. A 50, 4109 (1994).
[3] Th. Mercouris, Y. Komninos and C. A. Nicolaides, 'Time-dependent formation of the profile of the He 2s2p ^{1}P^{0} state excited by a short laser pulse', Phys. Rev. A 75, 013407 (2007).
[4] Th. Mercouris, Y. Komninos and C. A. Nicolaides, 'Time-resolved hyperfast processes of strongly correlated electrons during the coherent excitation and decay of multiply excited and inner-hole excited states', Phys. Rev. A 76, 033417 (2007).
[5] Y. Komninos, Th. Mercouris and C. A. Nicolaides, 'Ab initio calculation of time-dependent control dynamics in polyelectronic systems involving bound and resonance states: Application to a quartet spectrum of He- ', Phys. Rev. A 77, 013412 (2008).

Contact
T. Mercouris and C. A. Nicolaides
Theoretical and Physical Chemistry Institute,
National Hellenic Research Foundation,
48 Vassileos Constantinou Ave.,
Athens 11635, Greece