Abstract
A relativistic transient absorption theory is derived, implemented and validated within the dipole approximation based on the time-dependent Dirac equation. In the non-relativistic limit, it is found that the absorption agrees with the well established non-relativistic theory based on the time-dependent Schrödringer equation. Time-dependent simulations have been performed using the Dirac equation and the Schrödinger equation for the hydrogen atom in two different attosecond transient absorption scenarios. These simulations validate the present relativistic theory. The presented work can be seen as a first step in the development of a more general relativistic attosecond transient absorption spectroscopy method for studying heavy atoms, but it also suggests the possibility of studying relativistic effects, such as Zitterbewegung, in the time domain.
Highlights
Femtochemistry has opened the possibility of studying molecular motion thanks to the development of ultra-short laser pulses [1]
We have derived a general relativistic transient absorption theory which is based on the time-dependent Dirac equation (TDDE)
The relativistic dynamics of an electron embedded in the field of an atomic nucleus is described by the time-dependent Dirac equation (TDDE) which is defined as follows, ih
Summary
Femtochemistry has opened the possibility of studying molecular motion thanks to the development of ultra-short laser pulses [1]. Many experimental ideas have been transfer from the femtosecond to the attosecond domain An example of this is attosecond transient absorption spectroscopy (ATAS), which is used to study electron coherence and motion in atoms [3, 4, 5]. All studies so far are based on non-relativistic ATAS theory [14], but with spin-orbit corrections added in some cases. Pabst et al treated a strong near-infrared pump-pulse, and an overlapping XUV probe pulse, using the time-dependent configuration interaction singles (TDCIS) approach with an ad hoc Pauli-type spin-orbit correction on to the occupied states. We have derived a general relativistic transient absorption theory which is based on the time-dependent Dirac equation (TDDE).
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