Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review A

Alternating absorption features during attosecond-pulse propagation in a laser-controlled gaseous medium

Adrian Nikolaus Pfeiffer, M. Justine Bell, Annelise R. Beck, Hiroki Mashiko, Daniel M. Neumark, Stephen R. Leone

Published Nov 20, 2013• 37 citations
Publisher

Abstract

Recording the transmitted spectrum of a weak attosecond pulse through a medium, while a strong femtosecond pulse copropagates at variable delay, probes the strong-field dynamics of atoms, molecules, and solids. Usually, the interpretation of these measurements is based on the assumption of a thin medium. Here, the propagation through a macroscopic medium of helium atoms in the region of fully allowed resonances is investigated both theoretically and experimentally. The propagation has dramatic effects on the transient spectrum even at relatively low pressures (50 mbar) and short propagation lengths (1 mm). The absorption does not evolve monotonically with the product of propagation distance and pressure, but regions with characteristics of Lorentz line shapes and characteristics of Fano line shapes alternate. Criteria are deduced to estimate whether macroscopic effects can be neglected or not in a transient absorption experiment. Furthermore, the theory in the limit of single-atom response yields a general equation for Lorentz- and Fano-type line shapes at variable pulse delay.

DOI
10.1103/physreva.88.051402

Related papers

Attosecond transient absorption in dense gases: Exploring the interplay between resonant pulse propagation and laser-induced line-shape control

Chen-Ting Liao, Arvinder S. Sandhu, Seth Camp +2 more

We investigate the evolution of extreme ultraviolet (XUV) spectral line shapes in an optically thick helium gas under near-infrared (IR) perturbation. In our experimental and theoretical work, we systematically vary the IR intensity, time-delay, gas density, and IR polarization parameters to study line-shape modifications induced by collective interactions in a regime beyond the single-atom response of a thin, dilute gas. In both experiment and theory, we find that specific features in the frequency-domain absorption profile, and their evolution with propagation distance, can be attributed to the interplay between resonant attosecond pulse propagation and IR-induced phase shifts. Our calculations show that this interplay also manifests itself in the time domain, with the IR pulse influencing the reshaping of the XUV pulse propagating in the resonant medium.

arXiv:1602.01526•Physical Review A•Mar 4, 2016•24 citations

Watching the formation and reshaping of a Fano resonance in a macroscopic medium

Yu He, Zuoye Liu, Nan Xue +4 more

Time-resolved buildup of a Fano resonance in a macroscopic gaseous medium is theoretically studied by attosecond transient absorption spectroscopy. An intense near-infrared field is employed as an adjustable gate to confine the temporal dynamics, enabling one to resolve the line-shape formation in real time. Beyond the region where the single-atom approximation holds, we observe the emergence of spectral spikes with narrow linewidths for certain time delays and propagation distances, which represents that the medium can be delicately structured to be an efficient resonant absorber. Spectral substructures appear on the shoulder of the absorption lines after additional pulse propagation. The links between these features imprinted in spectral profiles and the formation of temporal characteristics in the excitation field are identified. The collective response of the medium versus time delay and propagation distance, in this laser-gated case, provides clues to the time-domain information on autoionization state and the microscopic dynamics occurring at each layer of the medium.

Physical Review A•Apr 15, 2021•12 citations

Absorption and emission of single attosecond light pulses in an autoionizing gaseous medium dressed by a time-delayed control field

Wei-Chun Chu, C. D. Lin

An extreme ultraviolet (EUV) single attosecond pulse passing through a laser-dressed dense gas is studied theoretically. The weak EUV pulse pumps the helium gas from the ground state to the $2s2p({}^{1}P)$ autoionizing state, which is coupled to the $2{s}^{2}{(}^{1}S)$ autoionizing state by a femtosecond infrared laser with the intensity in the order of 10${}^{12}$ W/cm${}^{2}$. The simulation shows how the transient absorption and emission of the EUV are modified by the coupling laser. A simple analytical expression for the atomic response derived for $\ensuremath{\delta}$-function pulses reveals the strong modification of the Fano lineshape in the spectra, where these features are quite universal and remain valid for realistic pulse conditions. We further account for the propagation of pulses in the medium and show that the EUV signal at the atomic resonance can be enhanced in the gaseous medium by more than 50$%$ for specifically adjusted laser parameters, and that this enhancement persists as the EUV propagates in the gaseous medium. Our result demonstrates the high-level control of nonlinear optical effects that are achievable with attosecond pulses.

arXiv:1211.6172•Physical Review A•Jan 16, 2013•45 citations

Resonant propagation of extreme-ultraviolet pulses through strongly driven high-density media

Yu He, Shuyuan Hu, Gergana Dimitrova Borisova +6 more

We show that by combining strong-field dressing and resonant propagation of XUV pulses, the transition of absorption lines from their natural Lorentzian profiles through Fano and complex multipeak shapes all the way back to broadened near-Lorentzian profiles can be achieved, in the limit of optically thick samples. The final stage of this spectral modification can be understood in terms of a significant temporal stretching and delay of the resonant XUV pulse as it propagates through the dense gas, which alters the ultrafast absorption that is modified by the time-synchronized few-femtosecond laser pulse. We first demonstrate this concept in numerical calculations, both using a model system and through a fully coupled solution of the time-dependent Schrödinger equation and the Maxwell wave equation. The applicability and generality of the underlying mechanism is then illustrated in proof-of-principle attosecond transient absorption measurements in a helium gas with a widely varying atomic density. These results provide insights into the interaction of ultrashort laser pulses with dense media and its coherent control.

Physical Review Research•Apr 16, 2025•3 citations

Laser-imposed phase in resonant absorption of an isolated attosecond pulse

Shaohao Chen, Mengxi Wu, Mette B. Gaarde +1 more

We calculate resonant absorption line shapes in helium atoms subject to the combination of an attosecond pulse of XUV radiation and a delayed, few-cycle infrared (IR) laser pulse. We are in particular interested in how the resonant features evolve with the delay between the fields and with increasing IR intensity. We first compare the single-atom absorption calculated by a nonperturbative solution of the time-dependent Schr\"odinger equation (TDSE) to a simple model in which the resonant absorption is modified only by a laser-imposed phase (LIP) that originates in the instantaneous ac Stark shift of the resonant state. We find that the LIP model can explain many features of the resonant absorption, including the direction of the resonance energy shift and the onset of dispersive line shapes with increasing IR intensity. We also find, however, that the LIP model predicts the energy shifts and the line shapes only qualitatively when the resonant states are strongly IR coupled to nearby states. We then use a coupled solution of the Maxwell wave equation and the TDSE to examine how the line shapes are modified by propagation effects at helium densities such that the resonant absorption is strong. We find that when the resonant absorption saturates, their line shapes are strongly modified due to reshaping of the attosecond pulse time profile during propagation. This in turn alters the ultrafast absorption and emission dynamics.

Physical Review A•Sep 9, 2013•56 citations

Beyond the Single-Atom Response in Absorption Line Shapes: Probing a Dense, Laser-Dressed Helium Gas with Attosecond Pulse Trains

Chen-Ting Liao, Arvinder S. Sandhu, Seth Camp +2 more

We investigate the absorption line shapes of laser-dressed atoms beyond the single-atom response, by using extreme ultraviolet (XUV) attosecond pulse trains to probe an optically thick helium target under the influence of a strong infrared (IR) field. We study the interplay between the IR-induced phase shift of the microscopic time-dependent dipole moment and the resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our experimental and theoretical results show that as the optical depth increases, this interplay leads initially to a broadening of the IR-modified line shape, and subsequently, to the appearance of new, narrow features in the absorption line.

arXiv:1503.02575•Physical Review Letters•Apr 6, 2015•50 citations
Recording the transmitted spectrum of a weak attosecond pulse through a medium, while a strong femtosecond pulse copropagates at variable delay, probes the strong-field dynamics of atoms, molecules, and solids. Usually, the interpretation of these measurements is based on the assumption of a thin medium. Here, the propagation through a macroscopic medium of helium atoms in the region of fully allowed resonances is investigated both theoretically and experimentally. The propagation has dramatic effects on the transient spectrum even at relatively low pressures (50 mbar) and short propagation lengths (1 mm). The absorption does not evolve monotonically with the product of propagation distance and pressure, but regions with characteristics of Lorentz line shapes and characteristics of Fano line shapes alternate. Criteria are deduced to estimate whether macroscopic effects can be neglected or not in a transient absorption experiment. Furthermore, the theory in the limit of single-atom response yields a general equation for Lorentz- and Fano-type line shapes at variable pulse delay.
We investigate the evolution of extreme ultraviolet (XUV) spectral line shapes in an optically thick helium gas under near-infrared (IR) perturbation. In our experimental and theoretical work, we systematically vary the IR intensity, time-delay, gas density, and IR polarization parameters to study line-shape modifications induced by collective interactions in a regime beyond the single-atom response of a thin, dilute gas. In both experiment and theory, we find that specific features in the frequency-domain absorption profile, and their evolution with propagation distance, can be attributed to the interplay between resonant attosecond pulse propagation and IR-induced phase shifts. Our calculations show that this interplay also manifests itself in the time domain, with the IR pulse influencing the reshaping of the XUV pulse propagating in the resonant medium.
Time-resolved buildup of a Fano resonance in a macroscopic gaseous medium is theoretically studied by attosecond transient absorption spectroscopy. An intense near-infrared field is employed as an adjustable gate to confine the temporal dynamics, enabling one to resolve the line-shape formation in real time. Beyond the region where the single-atom approximation holds, we observe the emergence of spectral spikes with narrow linewidths for certain time delays and propagation distances, which represents that the medium can be delicately structured to be an efficient resonant absorber. Spectral substructures appear on the shoulder of the absorption lines after additional pulse propagation. The links between these features imprinted in spectral profiles and the formation of temporal characteristics in the excitation field are identified. The collective response of the medium versus time delay and propagation distance, in this laser-gated case, provides clues to the time-domain information on autoionization state and the microscopic dynamics occurring at each layer of the medium.
An extreme ultraviolet (EUV) single attosecond pulse passing through a laser-dressed dense gas is studied theoretically. The weak EUV pulse pumps the helium gas from the ground state to the 2s2p(1P)2s2p({}^{1}P)2s2p(1P) autoionizing state, which is coupled to the 2s2(1S)2{s}^{2}{(}^{1}S)2s2(1S) autoionizing state by a femtosecond infrared laser with the intensity in the order of 1012{}^{12}12 W/cm2{}^{2}2. The simulation shows how the transient absorption and emission of the EUV are modified by the coupling laser. A simple analytical expression for the atomic response derived for $\ensuremath{\delta}$-function pulses reveals the strong modification of the Fano lineshape in the spectra, where these features are quite universal and remain valid for realistic pulse conditions. We further account for the propagation of pulses in the medium and show that the EUV signal at the atomic resonance can be enhanced in the gaseous medium by more than 50% for specifically adjusted laser parameters, and that this enhancement persists as the EUV propagates in the gaseous medium. Our result demonstrates the high-level control of nonlinear optical effects that are achievable with attosecond pulses.
We show that by combining strong-field dressing and resonant propagation of XUV pulses, the transition of absorption lines from their natural Lorentzian profiles through Fano and complex multipeak shapes all the way back to broadened near-Lorentzian profiles can be achieved, in the limit of optically thick samples. The final stage of this spectral modification can be understood in terms of a significant temporal stretching and delay of the resonant XUV pulse as it propagates through the dense gas, which alters the ultrafast absorption that is modified by the time-synchronized few-femtosecond laser pulse. We first demonstrate this concept in numerical calculations, both using a model system and through a fully coupled solution of the time-dependent Schrödinger equation and the Maxwell wave equation. The applicability and generality of the underlying mechanism is then illustrated in proof-of-principle attosecond transient absorption measurements in a helium gas with a widely varying atomic density. These results provide insights into the interaction of ultrashort laser pulses with dense media and its coherent control.
We calculate resonant absorption line shapes in helium atoms subject to the combination of an attosecond pulse of XUV radiation and a delayed, few-cycle infrared (IR) laser pulse. We are in particular interested in how the resonant features evolve with the delay between the fields and with increasing IR intensity. We first compare the single-atom absorption calculated by a nonperturbative solution of the time-dependent Schr\"odinger equation (TDSE) to a simple model in which the resonant absorption is modified only by a laser-imposed phase (LIP) that originates in the instantaneous ac Stark shift of the resonant state. We find that the LIP model can explain many features of the resonant absorption, including the direction of the resonance energy shift and the onset of dispersive line shapes with increasing IR intensity. We also find, however, that the LIP model predicts the energy shifts and the line shapes only qualitatively when the resonant states are strongly IR coupled to nearby states. We then use a coupled solution of the Maxwell wave equation and the TDSE to examine how the line shapes are modified by propagation effects at helium densities such that the resonant absorption is strong. We find that when the resonant absorption saturates, their line shapes are strongly modified due to reshaping of the attosecond pulse time profile during propagation. This in turn alters the ultrafast absorption and emission dynamics.
We investigate the absorption line shapes of laser-dressed atoms beyond the single-atom response, by using extreme ultraviolet (XUV) attosecond pulse trains to probe an optically thick helium target under the influence of a strong infrared (IR) field. We study the interplay between the IR-induced phase shift of the microscopic time-dependent dipole moment and the resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our experimental and theoretical results show that as the optical depth increases, this interplay leads initially to a broadening of the IR-modified line shape, and subsequently, to the appearance of new, narrow features in the absorption line.