© 2026 Aqora Quantum S.A.S.

Terms Privacy Legal Notice

Physical Review A

Single-atom response of helium atoms to pulses from an EUV free-electron laser: Implications for the subsequent development of superfluorescence

James Robert Harries, Chiaki Ohae, Susumu Kuma, Kyo Nakajima, Tadashi Togashi, Yuki Miyamoto, N. Sasao, Hiroshi Iwayama, Mitsuru Nagasono, Makina Yabashi, E. Shigemasa

Published Dec 22, 2016• 5 citations

Abstract

Using multilevel (161-level) numerical simulations beyond the rotating-wave approximation, we investigate the single-atom response of helium to intense pulses of radiation with properties characteristic of a self-amplified spontaneous emission (SASE) free-electron laser (FEL) source, and central wavelengths resonant with $1snp$ excitation ($n=3$,4). The results show a complete breakdown of the two-level approximation and suggest that, under typical experimental conditions, levels other than the resonant level are significantly populated. We discuss the implications for the subsequent development of superfluorescence (a collective effect) from the excited atomic medium and compare the results to recent experiments.

DOI: 10.1103/physreva.94.063416

Related papers

XUV superfluorescence from helium gas in the paraxial three-dimensional approximation

Špela Krušič, A. Mihelič, K. Bučar +3 more

We present the results of a theoretical study of XUV superfluorescence from doubly excited states of helium resonantly pumped by free-electron laser (FEL) pulses. Our model allows us to predict both the spectrum and angular distribution of emitted XUV radiation in a wide range of experimentally accessible parameters. This is achieved by going beyond two key deficiencies of most previous models: The one-dimensional treatment in space is upgraded to three dimensions with electromagnetic fields treated in the paraxial approximation and spontaneous emission is modeled by a recently developed approach that avoids the unrealistic delayed response but preserves the expected characteristics of the emitted field in the spontaneous emission limit. The case study of $3a{\phantom{\rule{0.16em}{0ex}}}^{1}{P}^{o}$ resonance in helium with $63.66\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ excitation energy is presented for realistic parameters of seeded light pulses from the FERMI FEL facility and a recently developed high-pressure gas cell. Results of numerical simulations show that both the spectral width and angular divergence of emitted radiation vary with gas pressure and pump pulse intensity in a complex way.

Physical Review A•Jan 24, 2023•4 citations

Superfluorescence (collective spontaneous emission) observed from helium atoms following excitation using an extreme-ultraviolet free-electron laser

ハリーズ　ジェームズ, ハリーズジェームズ

Using numerical simulations, and experiments at a free-electron laser, we have studied superfluorescence emission in helium atoms at visible wavelengths, and also observed strong directional emission at extreme ultraviolet wavelengths.

•Jul 31, 2017•0 citations

Superfluorescence, superradiance, and free-induction decay observed following the excitation of helium atoms and ions with FEL pulses from SACLA BL1

ハリーズ　ジェームズ, ハリーズジェームズ

Using EUV pulses from SACLA BL1 free-electron laser, we have successfully observed superfluorescence at wavelengths of 469 nm and 164 nm from a dense sample of excited helium ions, created by (1+1)-photon ionisation/excitation. The results of related numerical simulations will also be reported.

•Sep 11, 2017•0 citations

ヘリウムイオンの FEL 励起に伴う超蛍光、ヨーク超蛍光、自由誘導減衰、四光波混合

ハリーズ　ジェームズ, James Harries

We report the observation of superfluorescence at wavelengths of 469 nm, 164 nm and 30.4 nm from helium ions created and excited using pulses from the EUV free-electron laser at SACLA BL1. Experimental observations of intense, highly-directional emission (all 3 wavelengths) and a 1/(density) pulse delay dependence (469 nm emission), along with a detailed numerical simulation support our interpretations.

•Mar 17, 2019•0 citations

Observation of Free-Electron-Laser-Induced Collective Spontaneous Emission (Superfluorescence)

Mitsuru Nagasono, James Robert Harries, Hiroshi Iwayama +7 more

We have observed and characterized 501.6 nm collective spontaneous emission (superfluorescence) following 1s(2) → 1s3p excitation of helium atoms by 53.7 nm free-electron laser radiation. Emitted pulse energies of up to 100 nJ are observed, corresponding to a photon number conversion efficiency of up to 10%. We observe the peak intensity to scale as ρ(2) and the emitted pulse width and delay to scale as ρ(-1), where ρ is the atom number density. Emitted pulses as short as 1 ps are observed, which corresponds to a rate around 75,000 times faster than the spontaneous 1s3p → 1s2s decay rate. To our knowledge, this is the first observation of superfluorescence following pumping in the extreme ultraviolet wavelength region, and extension of the technique to the generation of extreme ultraviolet and x-ray superfluorescence pulses should be straightforward by using suitable atomic systems and pump wavelengths.

Physical Review Letters•Nov 1, 2011•46 citations

Collective effects in the radiative decay of the 2P1 state in helium

Špela Krušič, K. Bučar, A. Mihelič +1 more

We present a theoretical study of He $2\phantom{\rule{0.16em}{0ex}}^{1}P--2\phantom{\rule{0.16em}{0ex}}^{1}S$ emission from a helium gas, where the upper atomic state is prepared by a 100 fs laser pulse resonant with the $1\phantom{\rule{0.16em}{0ex}}^{1}S--2\phantom{\rule{0.16em}{0ex}}^{1}P$ transition. The fluorescence signal emitted in the forward direction at 2059 nm and the transmitted signal at $58.4\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ are followed in time starting with the low pump intensity regime where the single-atom spontaneous emission results in a characteristic exponential decay. By increasing the gas density and pump intensity, collective effects such as self-amplified spontaneous emission and superfluorescence modify the temporal dependence of the radiation field by amplifying the radiation pattern as well as changing its delay and intensity distribution. The extended Maxwell-Bloch simulation of the corresponding three-level $\mathrm{\ensuremath{\Lambda}}$ system in one spatial dimension covers emission delays of up to 2.4 ns, reaching beyond the natural lifetime of the $2\phantom{\rule{0.16em}{0ex}}^{1}P$ state.

Physical Review A•Jul 20, 2018•13 citations

Using multilevel (161-level) numerical simulations beyond the rotating-wave approximation, we investigate the single-atom response of helium to intense pulses of radiation with properties characteristic of a self-amplified spontaneous emission (SASE) free-electron laser (FEL) source, and central wavelengths resonant with

1snp

excitation (

n=3

,4). The results show a complete breakdown of the two-level approximation and suggest that, under typical experimental conditions, levels other than the resonant level are significantly populated. We discuss the implications for the subsequent development of superfluorescence (a collective effect) from the excited atomic medium and compare the results to recent experiments.

We present the results of a theoretical study of XUV superfluorescence from doubly excited states of helium resonantly pumped by free-electron laser (FEL) pulses. Our model allows us to predict both the spectrum and angular distribution of emitted XUV radiation in a wide range of experimentally accessible parameters. This is achieved by going beyond two key deficiencies of most previous models: The one-dimensional treatment in space is upgraded to three dimensions with electromagnetic fields treated in the paraxial approximation and spontaneous emission is modeled by a recently developed approach that avoids the unrealistic delayed response but preserves the expected characteristics of the emitted field in the spontaneous emission limit. The case study of

3a{\phantom{\rule{0.16em}{0ex}}}^{1}{P}^{o}

resonance in helium with

63.66\phantom{\rule{0.28em}{0ex}}\mathrm{eV}

excitation energy is presented for realistic parameters of seeded light pulses from the FERMI FEL facility and a recently developed high-pressure gas cell. Results of numerical simulations show that both the spectral width and angular divergence of emitted radiation vary with gas pressure and pump pulse intensity in a complex way.

We have observed and characterized 501.6 nm collective spontaneous emission (superfluorescence) following 1s(2) → 1s3p excitation of helium atoms by 53.7 nm free-electron laser radiation. Emitted pulse energies of up to 100 nJ are observed, corresponding to a photon number conversion efficiency of up to 10%. We observe the peak intensity to scale as ρ(2) and the emitted pulse width and delay to scale as ρ(-1), where ρ is the atom number density. Emitted pulses as short as 1 ps are observed, which corresponds to a rate around 75,000 times faster than the spontaneous 1s3p → 1s2s decay rate. To our knowledge, this is the first observation of superfluorescence following pumping in the extreme ultraviolet wavelength region, and extension of the technique to the generation of extreme ultraviolet and x-ray superfluorescence pulses should be straightforward by using suitable atomic systems and pump wavelengths.

We present a theoretical study of He

2\phantom{\rule{0.16em}{0ex}}^{1}P--2\phantom{\rule{0.16em}{0ex}}^{1}S

emission from a helium gas, where the upper atomic state is prepared by a 100 fs laser pulse resonant with the

1\phantom{\rule{0.16em}{0ex}}^{1}S--2\phantom{\rule{0.16em}{0ex}}^{1}P

transition. The fluorescence signal emitted in the forward direction at 2059 nm and the transmitted signal at

58.4\phantom{\rule{0.28em}{0ex}}\mathrm{nm}

are followed in time starting with the low pump intensity regime where the single-atom spontaneous emission results in a characteristic exponential decay. By increasing the gas density and pump intensity, collective effects such as self-amplified spontaneous emission and superfluorescence modify the temporal dependence of the radiation field by amplifying the radiation pattern as well as changing its delay and intensity distribution. The extended Maxwell-Bloch simulation of the corresponding three-level $\mathrm{\ensuremath{\Lambda}}$ system in one spatial dimension covers emission delays of up to 2.4 ns, reaching beyond the natural lifetime of the

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

state.