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arXiv:1208.5651 · Optics Letters

Interference-induced peak splitting in extreme ultraviolet superfluorescence

Ni Cui, Christoph H. Keitel, Mihai Macovei

Published Feb 12, 2013• 4 citations
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Abstract

We investigate the laser-induced quantum interference in extreme ultraviolet superfluorescence (SF) occurring in a dense gas of Λ-type helium atoms coupled by a coherent laser field in the visible region. Due to the constructive interatomic and intraatomic interferences, the SF can split in two pulses conveniently controlled by the gas density and intensity of the driving field, suggesting potential applications for pump-probe experiments.

DOI
10.1364/ol.38.000570

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We investigate the laser-induced quantum interference in extreme ultraviolet superfluorescence (SF) occurring in a dense gas of Λ-type helium atoms coupled by a coherent laser field in the visible region. Due to the constructive interatomic and intraatomic interferences, the SF can split in two pulses conveniently controlled by the gas density and intensity of the driving field, suggesting potential applications for pump-probe experiments.
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Intense x-ray and extreme ultraviolet (XUV) light sources have been available for decades, however, due to weak nonlinear interaction in the XUV photon energy range, observation of Rabi oscillation induced by XUV pulse remains a very challenging experimental task. Here we suggest a scheme where photoionization of a He medium by an intense XUV pump pulse is followed by a strong population inversion and Rabi oscillation at the He^{+}(1s-3p) transition and is accompanied by superfluorescence (SF) of the 7.56 eV pulse at the He^{+}(3p-2s) transition. Our numerical simulations show that the Rabi oscillation at the He^{+}(1s-3p) transition induced by an XUV pulse with photon energy 48.36 eV results in significant signatures in the SF spectra, allowing us to identify and characterize the XUV induced Rabi-oscillatory regime. The proposed scheme provides a sensitive tool to monitor and control ultrafast nonlinear dynamics in atoms and molecules triggered by intense XUV.
Atoms irradiated with combined femtosecond laser and extreme ultraviolet (XUV) fields ionize through multiphoton processes, even when the energy of the XUV photon is below the ionization potential. However, in the presence of two different XUV photons and an intense laser field, it is possible to induce full electromagnetic transparency. Taking helium as an example, the laser field modifies its electronic structure, while the presence of two different XUV photons and the laser field leads to two distinct ionization pathways that can interfere destructively. This work demonstrates a new approach for coherent control in a regime of highly excited states and strong optical fields.
We present a comprehensive experimental and theoretical study on superfluorescence in the extreme ultraviolet wavelength regime. Focusing a free-electron laser pulse in a cell filled with Xe gas, the medium is quasi-instantaneously population inverted by 4d-shell ionization on the giant resonance followed by Auger decay. On the timescale of ∼10 ps to ∼100 ps (depending on parameters) a macroscopic polarization builds up in the medium, resulting in superfluorescent emission of several Xe lines in the forward direction. As the number of emitters in the system is increased by either raising the pressure or the pump-pulse energy, the emission yield grows exponentially over four orders of magnitude and reaches saturation. With increasing yield, we observe line broadening, a manifestation of superfluorescence in the spectral domain. Our novel theoretical approach, based on a full quantum treatment of the atomic system and the irradiated field, shows quantitative agreement with the experiment and supports our interpretation.