Journal of Physics B Atomic Molecular and Optical Physics

Doubly resonant photoionization of He below the N = 2 ionization threshold

A. Mihelič, M. Žitnik, Mateja Hrast

Published Oct 26, 2017• 6 citations

Abstract

Abstract We present an extended theoretical study of two-colour doubly resonant photoionization of helium involving two doubly excited states below the N = 2 ionization threshold. We model the effects of a strong laser coupling between the lowest 1 P o and the selected 1 S e , 1 P e and 1 D e doubly excited states on the photoelectron (photoion) yield by taking into account the spatio-temporal structure of the pulses and by considering the effects of the neighbouring resonance states. We show that the laser coupling results in a measurable modification of the line profiles and in a reduction of the photoelectron yield under resonant or near-resonant conditions.

DOI: 10.1088/1361-6455/aa9621

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Journal of Physics B Atomic Molecular and Optical Physics

Doubly resonant photoionization of He below the N = 2 ionization threshold

A. Mihelič, M. Žitnik, Mateja Hrast

Published Oct 26, 2017• 6 citations

Publisher

Abstract

DOI: 10.1088/1361-6455/aa9621

Related papers

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Thomas Grosges, Bernard Piraux, H. Bachau

We study two-color photoionization of helium in the region of the $3s3d{}^{1}D$ autoionizing state with resonant excitation of the intermediate $2s2p{}^{1}P$ autoionizing state. We show that the corresponding time-dependent Schr\"odinger equation may be solved by expanding the total wave function on a few complex energy states. Perimetric coordinates are used to describe correlation effects accurately. Populations at the end of the interaction as well as photoionization probabilities are studied as a function of the laser pulse duration and both frequencies. Our calculations show that many continua play a crucial role at high intensities.We study two-color photoionization of helium in the region of the $3s3d{}^{1}D$ autoionizing state with resonant excitation of the intermediate $2s2p{}^{1}P$ autoionizing state. We show that the corresponding time-dependent Schr\"odinger equation may be solved by expanding the total wave function on a few complex energy states. Perimetric coordinates are used to describe correlation effects accurately. Populations at the end of the interaction as well as photoionization probabilities are studied as a function of the laser pulse duration and both frequencies. Our calculations show that many continua play a crucial role at high intensities.

Physical Review AAug 1, 199910 citations

We report time-resolved photoelectron spectroscopy of the

3s3p

doubly excited states of helium dressed by an intense near-infrared (NIR) laser field. Using synchronized XUV free-electron-laser and 800-nm NIR laser pulses, we observe a pronounced delay-dependent shift of resonance-related spectral minima together with the emergence of additional structures around the NIR sideband energy. \textit{Ab initio} theoretical calculations support these observations and identify the features as signatures of NIR-induced coupling of the bright (

3s3p {}^{1}P^{o}

) autoionizing state to nearby dark (

^{1}D^{e}

and

^{1}S^{e}

) resonances below the

N = 3

threshold. A multichannel Fano resonance analysis of the measured spectra yields delay-dependent line-shape parameters and resonance energies, establishing a quantitative route to characterize and control correlated two-electron resonances in strong laser fields.

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.

We study two-color photoionization of helium in the region of the

3s3d{}^{1}D

autoionizing state with resonant excitation of the intermediate

2s2p{}^{1}P

autoionizing state. We show that the corresponding time-dependent Schr\"odinger equation may be solved by expanding the total wave function on a few complex energy states. Perimetric coordinates are used to describe correlation effects accurately. Populations at the end of the interaction as well as photoionization probabilities are studied as a function of the laser pulse duration and both frequencies. Our calculations show that many continua play a crucial role at high intensities.