Journal of Physics Conference Series

Coupling of autoionizing states by a chirped laser pulse

M. Žitnik, A. Mihelič, K. Bučar, Mateja Hrast, Žiga Barba, Špela Krušič, Primož Rebernik Ribič, Jurij Urbančič, B. Ressel, Matija Stupar, Luca Poletto, Marcello Coreno, David Gauthier, Giovanni De Ninno

Published Jan 1, 2020• 0 citations

Publisher

Abstract

Synopsis We have observed the autoionization of the laser-coupled 2s2p 1 Po and 2p 2 1 Se resonances in helium. The ions were collected while varying the frequency and delay of the extreme-ultraviolet (EUV) excitation pulse with respect to the linearly chirped visible (VIS) laser pulse. From the measured frequency-delay map the Autler-Townes splitting, the EUV-VIS cross-correlation and the linear chirp parameter were extracted.

DOI: 10.1088/1742-6596/1412/8/082008

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Journal of Physics Conference Series

Coupling of autoionizing states by a chirped laser pulse

Published Jan 1, 2020• 0 citations

Publisher

Abstract

DOI: 10.1088/1742-6596/1412/8/082008

Related papers

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

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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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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.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.

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We present a method for measuring a complete frequency map of laser-dressed states with femtosecond lifetimes. It is based on collecting decay products as a function of the frequency of the excitation pulse and its delay with respect to the linearly chirped laser pulse, centered at the resonant transition frequency. The method has been tested on the case of laser-coupled $2s2p\phantom{\rule{4pt}{0ex}}^{1}P^{o}$ and $2{p}^{2}\phantom{\rule{4pt}{0ex}}^{1}S^{e}$ autoionizing resonances in He and is applicable to other quantum systems with short-lived states. When the laser coupling effects are known, the excitation pulse properties can be extracted from the map.We present a method for measuring a complete frequency map of laser-dressed states with femtosecond lifetimes. It is based on collecting decay products as a function of the frequency of the excitation pulse and its delay with respect to the linearly chirped laser pulse, centered at the resonant transition frequency. The method has been tested on the case of laser-coupled $2s2p\phantom{\rule{4pt}{0ex}}^{1}P^{o}$ and $2{p}^{2}\phantom{\rule{4pt}{0ex}}^{1}S^{e}$ autoionizing resonances in He and is applicable to other quantum systems with short-lived states. When the laser coupling effects are known, the excitation pulse properties can be extracted from the map.

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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.

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.

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.

2s2p\phantom{\rule{4pt}{0ex}}^{1}P^{o}

and

2{p}^{2}\phantom{\rule{4pt}{0ex}}^{1}S^{e}

autoionizing resonances in He and is applicable to other quantum systems with short-lived states. When the laser coupling effects are known, the excitation pulse properties can be extracted from the map.