Abstract
A theoretical description of attosecond transient absorption spectroscopy for temporally and spatially overlapping XUV and optical pulses is developed, explaining the signals one can obtain in such an experiment. To this end, we employ a two-stage approach based on perturbation theory, which allows us to give an analytical expression for the transient absorption signal. We focus on the situation in which the attosecond XUV pulse is used to create a coherent superposition of electronic states. As we explain, the resulting dynamics can be detected in the spectrum of the transmitted XUV pulse by manipulating the electronic wave packet using a carrier-envelope-phase-stabilized optical dressing pulse. In addition to coherent electron dynamics triggered by the attosecond pulse, the transmitted XUV spectrum encodes information on electronic states made accessible by the optical dressing pulse. We illustrate these concepts through calculations performed for a few-level model.
Highlights
Transient absorption spectroscopy is a well-known technique for studying quantum dynamics on the femtosecond time scale [1,2]
We have presented an analytical theory of attosecond transient absorption (ATA) spectroscopy for perturbatively dressed systems
We have used a two-stage approach based on perturbation theory, allowing us to give an analytical expression for the attosecond-resolved transient absorption signal
Summary
Transient absorption spectroscopy is a well-known technique for studying quantum dynamics on the femtosecond time scale [1,2]. When applying an external electromagnetic field, it is possible to modify the absorption cross-section of an XUV or X-ray probe pulse. This allows observing the dynamics driven in the system by the field. As a function of the intensity of the applied external electromagnetic field different processes can be studied. In the case of optical tunnel ionization, probing after the strong-field pump pulse provides spectroscopic information about the residual ion, such as ion quantum state distributions [16,17] and orbital alignment [18,19]. Laser-dressing and molecular alignment effects may be investigated [20,21,22,23,24,25,26,27,28]
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