Atomic Siegert states in a circularly polarized laser field in a rotating frame

There is currently a strong interest in using intense circularly polarized laser pulses with wavelengths
in the near-Infrared region to study the interaction with atomic and molecular targets and considerable efforts
are being made on the theoretical side to understand these experimental outcomes. However, solving the
Time-dependent Schrödinger Equation (TDSE) is not feasible for realistic simulations and existing approximating
methods such as the Strong-Field-Approximation (SFA) have undesirable limitations.

Recently, a new promising alternative named the Adiabatic theory of Photoionization [1] (ADB) has been
developed and successfully applied in a various number of publications [2-4]. Provided that the ratio of the target
time scale and laser pulse time scale is small, which is the case of experimental interest here, it has been
shown to approach the TDSE uniformly in field strength of the pulse. This is in direct contrast with SFA, which
only applies to weak fields.

The ADB theory uses information obtained from Siegert states evaluated at specific saddle points in time
during the interaction. These states are solutions to the stationary Schrödinger equation satisfying regularity
and outgoing-wave boundary conditions and constitute a powerful tool in understanding ionization by static
electric fields; their eigenvalues give the ionization rates of the system while the eigenfunctions themselves
define the transverse momentum distribution of the ionized electrons in the outgoing flux.

Previously, these states have been constructed in the laboratory frame. However, for the case of circularly
polarized pulses the ADB theory could perform better in a rotating frame. This is the motivation for my
current project of developing a method to compute Atomic Siegert states in a rotating frame. In this talk I
will present the basic idea and initial results for parameters of current experimental interest.

References:

[1] Adiabatic theory of ionization by intense laser pulses: Finite-range potentials,
O. I. Tolstikhin and T. Morishita, Physical Review A 86, 043417 (2012)

[2] Near-Forward Rescattering Photoelectron Holography in Strong-Field Ionization:
Extraction of the Phase of the Scattering Amplitude, Y. Zhou, O. I. Tolstikhin and T. Morishita,
Physical Review Letters 116, 173001 (2016)

[3] Adiabatic theory of strong-field photoelectron momentum distributions near a
backward rescattering caustic, T. Morishita and O. I. Tolstikhin,
Physical Review A 96, 053416 (2017)

[4] Rescattering photoelectron spectroscopy of heterodiatomic molecules with an analytical returning
photoelectron wave packet, I Ito, M Okunishi, T. Morishita, O. I. Tolstikhin and K. Ueda,
Physical Review A 97, 053411 (2018)