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

Research in Optical Sciences

Time-domain Physics in Doubly-excited States and Phase Control of Fano Resonances

Thomas Pfeifer

Published Jan 1, 2014• 0 citations
Publisher

Abstract

Doubly-excited states of helium were coherently excited by attosecond-pulsed extreme-ultraviolet light, probed and controlled with near-visible intensity-tunable laser pulses. The results enabled the understanding of Fano resonances in the time domain and corresponding scientific applications.
DOI
10.1364/hilas.2014.hth4b.1

Related papers

Ultrafast Laser Control of Absorption and Emission via the Fano Phase

Thomas Pfeifer

Transmission of attosecond-pulsed light through Helium gas driven by few-cycle laser fields of tunable intensity allows to temporally resolve and control the process of absorption. The results enabled the understanding of Fano resonances in the time domain and corresponding scientific applications.

International Conference on Ultrafast Phenomena•Jan 1, 2014•0 citations

Fano Resonances in the Time Domain - understanding and controlling the absorption and emission of light

Andreas Kaldun

Fano Resonances in the Time Domain - understanding and controlling the absorption and emission of light—Within this work, starting from the well known theory for photoabsorption cross sections by Ugo Fano, a new formalism is developed, which enables measurement and control of phase and amplitude changes in an emitting dipole. This is shown by experimental measurements in singly and doubly excited helium that confirm the formalism. An application in time-domain quantum holography of excited states, allowing to separate laser-induced coupling pathways, is also presented.

•Jan 1, 2014•1 citation

Attosecond XUV absorption spectroscopy of doubly excited states in helium atoms dressed by a time-delayed femtosecond infrared laser

Z. Q. Yang, Difa Ye, Thomas Ding +2 more

In the present paper, we investigate the time-resolved transient absorption spectroscopy of doubly excited states of helium atoms by solving the time-dependent two-electron Schr\"odinger equation numerically based on a one-dimensional model. The helium atoms are subjected to an extreme ultraviolet (XUV) attosecond pulse and a time-delayed infrared (IR) few-cycle laser pulse. A superposition of doubly excited states populated by the XUV pulse is identified, which interferes with the direct ionization pathway leading to Fano resonance profiles in the photoabsorption spectrum. In the presence of an IR laser, however, the Fano line profiles are strongly modified: A shifting, splitting, and broadening of the original absorption lines is observed when the XUV attosecond pulse and infrared few-cycle laser pulse overlap in time, which is in good agreement with recent experimental results. At certain time delays, we observe symmetric Lorentz, inverted Fano profiles, and even negative absorption cross sections indicating that the XUV light can be amplified during the interaction with atoms. We further prove that the above pictures are general for different doubly excited states by suitably varying the frequency of the IR field to coherently couple the corresponding states.

Physical Review A•Jan 27, 2015•30 citations

Attosecond Transient Absorption Spectroscopy of doubly-excited states in helium

Luca Argenti, Christian Ott, Thomas Pfeifer +1 more

Strong-field manipulation of autoionizing states is a crucial aspect of electronic quantum control. Recent measurements of the attosecond transient absorption spectrum of helium dressed by a few-cycle visible pulse [Ott et al., arXiv:1205.0519[physics.atom-ph] ] provide evidence of novel ultrafast resonant phenomena, namely, two-photon Rabi oscillations between doubly-excited states and the inversion of Fano profiles. Here we present the results of accurate \emph{ab-initio} calculations that agree with these observations and in addition predict that (i) inversion of Fano profiles is actually periodic in the coupling laser intensity and (ii) the supposedly dark $2p^2$ {$^1$S} state also appears in the spectrum. Closer inspection of the experimental data confirms the latter prediction.

arXiv:1211.2566•Nov 12, 2012•2 citations

Ionization and transient absorption control with a resonant attosecond clock

Luca Argenti

Metastable states are important actors in the ionisation of atoms and molecules. Sub-femtosecond extreme ultraviolet pulses can coherently populate several transiently bound states at once, thus starting the attosecond clocks which are required to monitor and control ultrafast electronic evolution above the ionisation threshold. Here we illustrate, from a theoretical point of view, the effects coherent superpositions of 1 P o doubly excited states in the helium atom have on channel-resolved photoelectron spectra as well as on the transient absorption spectrum of the atom in the extreme ultraviolet region, when they are created by a single-attosecond pulse in the presence of a strong few-cycle near-infrared/visible pulse which acts as a probe. Interference fringes varying rapidly with the pump-probe time delay are visible in both photoelectron and transient absorption spectra. From such fringes, the wave packet itself can conceivably be reconstructed. Conversely, all observables are modulated by the characteristic beating periods of the wave packet, so that control of partial ionisation yields, branching ratios, and light absorption or amplification can be achieved.

Journal of Physics Conference Series•Apr 10, 2014•2 citations

Zeptosecond Control of Fano Line Shapes in Laser-Dressed Atoms Excited by Time-Delayed Attosecond Pulse Pairs

Yong Fu, Bincheng Wang, Xiangyu Tang +4 more

The attosecond pump-femtosecond probe technique is widely used in electron dynamics research, with temporal resolution reaching tens of attoseconds. Here, we propose a scheme for controlling the Fano line shapes of helium doubly excited states by replacing the pump source with a pair of time-delayed attosecond pulses. We show that the interference induced by this delay provides an additional, highly effective means of controlling electron dynamics, enabling temporal resolution on the zeptosecond scale. We demonstrate that the corresponding line shapes in transient absorption spectra can shift dramatically within a time-delay variation of just a few hundred zeptoseconds. This extreme spectral modulation occurs under two key conditions: (i) when the time delay aligns with the spectral minimum of the coherently combined attosecond pulses in the frequency domain, and (ii) when the delay between the infrared probe pulse and the first attosecond pulse is held constant. This approach opens a new pathway to zeptosecond-scale control in quantum systems and demonstrates the powerful synergy between phase manipulation in both light and electron waves for achieving ultrafast spectral transformations.

ACS Photonics•Apr 20, 2026•1 citation
Fano Resonances in the Time Domain - understanding and controlling the absorption and emission of light—Within this work, starting from the well known theory for photoabsorption cross sections by Ugo Fano, a new formalism is developed, which enables measurement and control of phase and amplitude changes in an emitting dipole. This is shown by experimental measurements in singly and doubly excited helium that confirm the formalism. An application in time-domain quantum holography of excited states, allowing to separate laser-induced coupling pathways, is also presented.
In the present paper, we investigate the time-resolved transient absorption spectroscopy of doubly excited states of helium atoms by solving the time-dependent two-electron Schr\"odinger equation numerically based on a one-dimensional model. The helium atoms are subjected to an extreme ultraviolet (XUV) attosecond pulse and a time-delayed infrared (IR) few-cycle laser pulse. A superposition of doubly excited states populated by the XUV pulse is identified, which interferes with the direct ionization pathway leading to Fano resonance profiles in the photoabsorption spectrum. In the presence of an IR laser, however, the Fano line profiles are strongly modified: A shifting, splitting, and broadening of the original absorption lines is observed when the XUV attosecond pulse and infrared few-cycle laser pulse overlap in time, which is in good agreement with recent experimental results. At certain time delays, we observe symmetric Lorentz, inverted Fano profiles, and even negative absorption cross sections indicating that the XUV light can be amplified during the interaction with atoms. We further prove that the above pictures are general for different doubly excited states by suitably varying the frequency of the IR field to coherently couple the corresponding states.
Strong-field manipulation of autoionizing states is a crucial aspect of electronic quantum control. Recent measurements of the attosecond transient absorption spectrum of helium dressed by a few-cycle visible pulse [Ott et al., arXiv:1205.0519[physics.atom-ph] ] provide evidence of novel ultrafast resonant phenomena, namely, two-photon Rabi oscillations between doubly-excited states and the inversion of Fano profiles. Here we present the results of accurate \emph{ab-initio} calculations that agree with these observations and in addition predict that (i) inversion of Fano profiles is actually periodic in the coupling laser intensity and (ii) the supposedly dark 2p22p^22p2 {1^11S} state also appears in the spectrum. Closer inspection of the experimental data confirms the latter prediction.
Metastable states are important actors in the ionisation of atoms and molecules. Sub-femtosecond extreme ultraviolet pulses can coherently populate several transiently bound states at once, thus starting the attosecond clocks which are required to monitor and control ultrafast electronic evolution above the ionisation threshold. Here we illustrate, from a theoretical point of view, the effects coherent superpositions of 1 P o doubly excited states in the helium atom have on channel-resolved photoelectron spectra as well as on the transient absorption spectrum of the atom in the extreme ultraviolet region, when they are created by a single-attosecond pulse in the presence of a strong few-cycle near-infrared/visible pulse which acts as a probe. Interference fringes varying rapidly with the pump-probe time delay are visible in both photoelectron and transient absorption spectra. From such fringes, the wave packet itself can conceivably be reconstructed. Conversely, all observables are modulated by the characteristic beating periods of the wave packet, so that control of partial ionisation yields, branching ratios, and light absorption or amplification can be achieved.
The attosecond pump-femtosecond probe technique is widely used in electron dynamics research, with temporal resolution reaching tens of attoseconds. Here, we propose a scheme for controlling the Fano line shapes of helium doubly excited states by replacing the pump source with a pair of time-delayed attosecond pulses. We show that the interference induced by this delay provides an additional, highly effective means of controlling electron dynamics, enabling temporal resolution on the zeptosecond scale. We demonstrate that the corresponding line shapes in transient absorption spectra can shift dramatically within a time-delay variation of just a few hundred zeptoseconds. This extreme spectral modulation occurs under two key conditions: (i) when the time delay aligns with the spectral minimum of the coherently combined attosecond pulses in the frequency domain, and (ii) when the delay between the infrared probe pulse and the first attosecond pulse is held constant. This approach opens a new pathway to zeptosecond-scale control in quantum systems and demonstrates the powerful synergy between phase manipulation in both light and electron waves for achieving ultrafast spectral transformations.