arXiv:1205.4766 · Physical Review A

Photoabsorption of attosecond XUV light pulses by two strongly laser-coupled autoionizing states

Wei-Chun Chu, C. D. Lin

Published Jan 11, 2012• 45 citations

Abstract

We study theoretically the photoabsorption spectra of an attosecond extreme ultraviolet (XUV) pulse by a laser-dressed atomic system. A weak XUV excites an autoionizing state which is strongly coupled to another autoionizing state by a laser. The theory was applied to explain two recent experiments [Loh, Greene, and Leone, Chem. Phys. 350, 7 (2008); Wang, Chini, Chen, Zhang, Cheng, He, Cheng, Wu, Thumm, and Chang, Phys. Rev. Lett. 105, 143002 (2010)] where the absorption spectra of the XUV lights were measured against the time delay between the laser and the XUV. In another example, we study an attosecond pulse exciting the $2s2p{(}^{1}\phantom{\rule{-0.16em}{0ex}}P)$ resonance of helium which is resonantly coupled to the $2{s}^{2}{(}^{1}\phantom{\rule{-0.16em}{0ex}}S)$ resonance by a moderately intense 540-nm laser. The relation between the photoabsorption spectra and the photoelectron spectra and the modification of the transmitted lights in such an experiment are analyzed. The role of Rabi flopping between the two autoionizing states within their lifetimes is investigated with respect to the laser intensity and detuning.

DOI: 10.1103/physreva.85.013409

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Laser-assisted-autoionization dynamics of helium resonances with single attosecond pulses

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

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Light-induced states in attosecond transient absorption spectra of laser-dressed helium

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Probing and Controlling Autoionization Dynamics with Attosecond Light Pulses in a Strong Dressing Laser Field

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Jan 1, 20131 citation

Transient absorption and reshaping of ultrafast XUV light by laser-dressed helium

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Femtosecond XUV transparency in light-coupled He doubly excited states.

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arXiv:1205.4766 · Physical Review A

Photoabsorption of attosecond XUV light pulses by two strongly laser-coupled autoionizing states

Wei-Chun Chu, C. D. Lin

Published Jan 11, 2012• 45 citations

arXiv HTML PDF

Abstract

2s2p{(}^{1}\phantom{\rule{-0.16em}{0ex}}P)

resonance of helium which is resonantly coupled to the

2{s}^{2}{(}^{1}\phantom{\rule{-0.16em}{0ex}}S)

resonance by a moderately intense 540-nm laser. The relation between the photoabsorption spectra and the photoelectron spectra and the modification of the transmitted lights in such an experiment are analyzed. The role of Rabi flopping between the two autoionizing states within their lifetimes is investigated with respect to the laser intensity and detuning.

DOI: 10.1103/physreva.85.013409

Related papers

Laser-assisted-autoionization dynamics of helium resonances with single attosecond pulses

Wei-Chun Chu, Song-Feng Zhao, C. D. Lin

The strong coupling between two autoionizing states in helium is studied theoretically with the pump-probe scheme. An isolated 100-as XUV pulse is used to excite helium near the $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ resonance state in the presence of an intense infrared (IR) laser. The laser field introduces strong coupling between $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ and $2{p}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)$ states. The IR also can ionize helium from both autoionizing states. By changing the time delay between the XUV and the IR pulses, we investigated the photoelectron spectra near the two resonances. The results are used to explain the recent experiment by Gilbertson et al. [Phys. Rev. Lett. 105, 263003 (2010)]. Using the same isolated attosecond pulse and a 540-nm laser, we also investigate the strong coupling between $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ and $2{s}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)$ by examining how the photoelectron spectra are modified versus the time delay and the possibility of observing Autler-Townes doublet in such experiments.The strong coupling between two autoionizing states in helium is studied theoretically with the pump-probe scheme. An isolated 100-as XUV pulse is used to excite helium near the $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ resonance state in the presence of an intense infrared (IR) laser. The laser field introduces strong coupling between $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ and $2{p}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)$ states. The IR also can ionize helium from both autoionizing states. By changing the time delay between the XUV and the IR pulses, we investigated the photoelectron spectra near the two resonances. The results are used to explain the recent experiment by Gilbertson et al. [Phys. Rev. Lett. 105, 263003 (2010)]. Using the same isolated attosecond pulse and a 540-nm laser, we also investigate the strong coupling between $2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)$ and $2{s}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)$ by examining how the photoelectron spectra are modified versus the time delay and the possibility of observing Autler-Townes doublet in such experiments.

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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.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.

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Light-induced states in attosecond transient absorption spectra of laser-dressed helium

Shaohao Chen, M. Justine Bell, Annelise R. Beck +7 more

Laser-dressed absorption in atomic helium is studied, both theoretically and experimentally, by transient absorption spectroscopy using isolated 400-as pulses centered at 22 eV and 12-fs near-infrared (NIR) pulses with 780-nm central wavelength. Multiple features in the helium singly excited bound-state spectrum are observed only when the NIR and attosecond pulses are overlapped in time. Theoretical analysis indicates that these light-induced structures (LISs) are the intermediate states in resonant, second-order processes that transfer population to multiple dipole forbidden states. The use of broadband, coherent extreme ultraviolet (XUV) radiation allows observation of these LISs without specifically tuning to a two-photon resonance, as would be required with narrowband XUV light. The strength and position of the LISs depend strongly on the NIR intensity and the pump-probe delay.Laser-dressed absorption in atomic helium is studied, both theoretically and experimentally, by transient absorption spectroscopy using isolated 400-as pulses centered at 22 eV and 12-fs near-infrared (NIR) pulses with 780-nm central wavelength. Multiple features in the helium singly excited bound-state spectrum are observed only when the NIR and attosecond pulses are overlapped in time. Theoretical analysis indicates that these light-induced structures (LISs) are the intermediate states in resonant, second-order processes that transfer population to multiple dipole forbidden states. The use of broadband, coherent extreme ultraviolet (XUV) radiation allows observation of these LISs without specifically tuning to a two-photon resonance, as would be required with narrowband XUV light. The strength and position of the LISs depend strongly on the NIR intensity and the pump-probe delay.

Physical Review ADec 17, 2012145 citations

Probing and Controlling Autoionization Dynamics with Attosecond Light Pulses in a Strong Dressing Laser Field

Wei-chun Chu, Tōru Morishita, C. D. Lin

We review the theoretical investigations of the autoionzing wave packet excited by an isolated attosecond pulse and dressed by a time-delayed intense laser pulse. The few-level model is described and the applications in photoemission and photoabsorption are given. For the three-level, resonantly coupled system, the main features are explained by the Rabi oscillation modulated in the dressing field. For such a system, by precisely controlling the intensity and the time delay of the dressing pulse, we show the shaping of the attosecond pulse when propagating in a gas medium. A more sophisticated multi-level system with coupling terms involving continuum states is also developed, in which the importance of the continuum-continuum coupling is evaluated with the help of an ab initio calculation. DOI: PACS numbers: 32.80.Qk, 32.80.Zb, 42.50.Gy I.We review the theoretical investigations of the autoionzing wave packet excited by an isolated attosecond pulse and dressed by a time-delayed intense laser pulse. The few-level model is described and the applications in photoemission and photoabsorption are given. For the three-level, resonantly coupled system, the main features are explained by the Rabi oscillation modulated in the dressing field. For such a system, by precisely controlling the intensity and the time delay of the dressing pulse, we show the shaping of the attosecond pulse when propagating in a gas medium. A more sophisticated multi-level system with coupling terms involving continuum states is also developed, in which the importance of the continuum-continuum coupling is evaluated with the help of an ab initio calculation. DOI: PACS numbers: 32.80.Qk, 32.80.Zb, 42.50.Gy I.

Jan 1, 20131 citation

Transient absorption and reshaping of ultrafast XUV light by laser-dressed helium

Mette B. Gaarde, Christian Buth, Jennifer L. Tate +1 more

We present a theoretical study of transient absorption and reshaping of extreme ultraviolet (XUV) pulses by helium atoms dressed with a moderately strong infrared (IR) laser field. We formulate the atomic response using both the frequency-dependent absorption cross section and a time-frequency approach based on the time-dependent dipole induced by the light fields. The latter approach can be used in cases when an ultrafast dressing pulse induces transient effects, and/or when the atom exchanges energy with multiple frequency components of the XUV field. We first characterize the dressed atom response by calculating the frequency-dependent absorption cross section for XUV energies between 20 and 24 eV for several dressing wavelengths between 400 and 2000 nm and intensities up to 10 ${}^{12}$ W/cm ${}^{2}$ . We find that for dressing wavelengths near 1600 nm, there is an Autler-Townes splitting of the $1s\ensuremath{\rightarrow}2p$ transition that can potentially lead to transparency for absorption of XUV light tuned to this transition. We study the effect of this XUV transparency in a macroscopic helium gas by incorporating the time-frequency approach into a solution of the coupled Maxwell-Schr\"odinger equations. We find rich temporal reshaping dynamics when a 61-fs XUV pulse resonant with the $1s\ensuremath{\rightarrow}2p$ transition propagates through a helium gas dressed by an 11-fs, 1600-nm laser pulse.We present a theoretical study of transient absorption and reshaping of extreme ultraviolet (XUV) pulses by helium atoms dressed with a moderately strong infrared (IR) laser field. We formulate the atomic response using both the frequency-dependent absorption cross section and a time-frequency approach based on the time-dependent dipole induced by the light fields. The latter approach can be used in cases when an ultrafast dressing pulse induces transient effects, and/or when the atom exchanges energy with multiple frequency components of the XUV field. We first characterize the dressed atom response by calculating the frequency-dependent absorption cross section for XUV energies between 20 and 24 eV for several dressing wavelengths between 400 and 2000 nm and intensities up to 10${}^{12}$ W/cm${}^{2}$. We find that for dressing wavelengths near 1600 nm, there is an Autler-Townes splitting of the $1s\ensuremath{\rightarrow}2p$ transition that can potentially lead to transparency for absorption of XUV light tuned to this transition. We study the effect of this XUV transparency in a macroscopic helium gas by incorporating the time-frequency approach into a solution of the coupled Maxwell-Schr\"odinger equations. We find rich temporal reshaping dynamics when a 61-fs XUV pulse resonant with the $1s\ensuremath{\rightarrow}2p$ transition propagates through a helium gas dressed by an 11-fs, 1600-nm laser pulse.

arXiv:1010.4558Physical Review AJan 31, 2011182 citations

Femtosecond XUV transparency in light-coupled He doubly excited states.

Michal Tarana, Chris H. Greene

Frontiers in OpticsJan 1, 20110 citations

2s2p{(}^{1}\phantom{\rule{-0.16em}{0ex}}P)

resonance of helium which is resonantly coupled to the

2{s}^{2}{(}^{1}\phantom{\rule{-0.16em}{0ex}}S)

The strong coupling between two autoionizing states in helium is studied theoretically with the pump-probe scheme. An isolated 100-as XUV pulse is used to excite helium near the

2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)

resonance state in the presence of an intense infrared (IR) laser. The laser field introduces strong coupling between

2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)

and

2{p}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)

states. The IR also can ionize helium from both autoionizing states. By changing the time delay between the XUV and the IR pulses, we investigated the photoelectron spectra near the two resonances. The results are used to explain the recent experiment by Gilbertson et al. [Phys. Rev. Lett. 105, 263003 (2010)]. Using the same isolated attosecond pulse and a 540-nm laser, we also investigate the strong coupling between

2s2p{(}^{1}\phantom{\rule{0.16em}{0ex}}P)

and

2{s}^{2}{(}^{1}\phantom{\rule{0.16em}{0ex}}S)

by examining how the photoelectron spectra are modified versus the time delay and the possibility of observing Autler-Townes doublet in such experiments.

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.

{}^{12}

W/cm

{}^{2}

. We find that for dressing wavelengths near 1600 nm, there is an Autler-Townes splitting of the $1s\ensuremath{\rightarrow}2p$ transition that can potentially lead to transparency for absorption of XUV light tuned to this transition. We study the effect of this XUV transparency in a macroscopic helium gas by incorporating the time-frequency approach into a solution of the coupled Maxwell-Schr\"odinger equations. We find rich temporal reshaping dynamics when a 61-fs XUV pulse resonant with the $1s\ensuremath{\rightarrow}2p$ transition propagates through a helium gas dressed by an 11-fs, 1600-nm laser pulse.