The role of transition dipole phase in atomic attosecond transient absorption from the multi-level model

Guanglu Yuan,Shicheng Jiang,Ziwen Wang,Weijie Hua,Ruifeng Lu,Chao Yu,Cheng Jin

doi:10.1063/1.5124441

Abstract

Based on a multilevel model considering enough bound electronic states of atoms, we theoretically study the role of the transition dipole phase (TDP) in the attosecond transient absorption (ATA) spectrum of helium in intense laser fields. By solving the stationary Schrödinger equation with B-spline basis sets, we first calculate the transition dipole moments with well-defined phases between the bound states. Using the modified multilevel model, we reveal that the TDP plays an important role in determining the spectral structures if two or more paths populate the excited states from the ground state. Our multilevel model with the accurate TDP is convenient to address the origin of atomic ATA spectral structures by freely removing or adding specific electronic states and has been justified by comparing with the ATA spectra via directly solving the time-dependent Schrödinger equation. Hopefully, further incorporating macroscopic propagation into the model will provide indepth physical insights into experimental ATA spectra.

Highlights

From the interaction of an intense focused laser with a gaseous medium, the generated high harmonics have been established as a tabletop light source to produce the isolated attosecond pulse or the attosecond pulse train in the extreme ultraviolet (XUV).[1,2,3,4,5,6,7] Such an attosecond XUV field can be precisely synchronized with a moderate infrared (IR) laser to offer a scheme for the so-called attosecond transient absorption (ATA) spectroscopy in a time-resolved way to trace the rapid electronic dynamics at the sub-optical-cycle scale
Based on a multilevel model considering enough bound electronic states of atoms, we theoretically study the role of the transition dipole phase (TDP) in the attosecond transient absorption (ATA) spectrum of helium in intense laser fields
We theoretically obtained the well-defined phase of the transition dipole moment between the bound atomic states by numerically solving the stationary Schr€odinger equation with the Bspline basis set and proposed a modified multilevel model accounting for the phase of the transition dipole

Summary

Introduction

From the interaction of an intense focused laser with a gaseous medium, the generated high harmonics have been established as a tabletop light source to produce the isolated attosecond pulse or the attosecond pulse train in the extreme ultraviolet (XUV).[1,2,3,4,5,6,7] Such an attosecond XUV field can be precisely synchronized with a moderate infrared (IR) laser to offer a scheme for the so-called attosecond transient absorption (ATA) spectroscopy in a time-resolved way to trace the rapid electronic dynamics at the sub-optical-cycle scale. The ATA spectrum is a fully optical method, using a femtosecond IR pulse to dress the system so that the spectrum of an attosecond XUV pulse transmitted through a sample and recorded as a function of time delay with respect to the IR pulse is modified, providing the information of absorption and emission of light. This technique has less disturbance to the target system than the detection of charged particles, and so the experimental signal-to-noise ratio is higher.

Methods

Results

Conclusion