Efficiency of dopant-induced ignition of helium nanoplasmas

Heidenreich, Andreas; Grüner, B.; Rometsch, M; Krishnan, S. S.; Stienkemeier, F.; Mudrich, M.

doi:10.1088/1367-2630/18/7/073046

Cited by 25 publications

(49 citation statements)

References 47 publications

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“…This links to our previous work where the interplay between dopant and He ionization during nanoplasma formation was studied [13,14]. We shall show that a partial loss of seed electrons plays an important role in the opening of the EII channel of He in Ca doped droplets.…”

Section: Deshielding Of the Dopant Cationssupporting

confidence: 76%

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Dopant-induced ignition of helium nanoplasmas—a mechanistic study

Heidenreich¹,

Schomas²,

Mudrich³

2017

J. Phys. B: At. Mol. Opt. Phys.

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Abstract. Helium (He) nanodroplets irradiated by intense near-infrared laser pulses form a nanoplasma by avalanche-like electron impact ionizations even at lower laser intensities where He is not directly field ionized, provided that the droplets contain a few dopant atoms which provide seed electrons for the electron impact ionization avalanche. In this theoretical paper on calcium and xenon doped He droplets we elucidate the mechanism which induces ionization avalanches, termed ignition. We find that the partial loss of seed electrons from the activated droplets starkly assists ignition, as the Coulomb barrier for ionization of helium is lowered by the electric field of the dopant cations, and this deshielding of the cation charges enhances their electric field. In addition, the dopant ions assist the acceleration of the seed electrons (slingshot effect) by the laser field, supporting electron impact ionizations of He and also causing electron loss by catapulting electrons away. The dopants' ability to lower the Coulomb barriers at He as well as the slingshot effect decrease with the spatial expansion of the dopant, causing a dependence of the dopants' ignition capability on the dopant mass. Here, we develop criteria (impact count functions) to assess the ignition capability of dopants, based on (i) the spatial overlap of the seed electron cloud with the He atoms and (ii) the overlap of their kinetic energy distribution with the distribution of Coulomb barrier heights at He. The relatively long time delays between the instants of dopant ionization and ignition (incubation times) for calcium doped droplets are determined to a large extent by the time it takes to deshield the dopant ions.

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Section: Deshielding Of the Dopant Cationssupporting

confidence: 76%

“…We previously described the molecular dynamics (MD) simulation method for the interaction of a cluster with a linearly polarized NIR Gaussian laser pulse [13,15,16]. Starting with a cluster of neutral atoms, electrons enter the simulation when the criteria for TI, BSI or EII apply.…”

Section: Simulationsmentioning

confidence: 99%

Dopant-induced ignition of helium nanoplasmas—a mechanistic study

Heidenreich¹,

Schomas²,

Mudrich³

2017

J. Phys. B: At. Mol. Opt. Phys.

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“…9c) and d), the absolute intensities of the He ion signals fall below those for Xe doping for any doping level; for Ca doping, the maximum He + intensity reached at about 3 Ca dopant atoms amounts to 8% of that achieved with Xe doping and for K doping the He + intensity remains below 0.3% of that of Xe doping [8]. Thus, the mass-over-charge spectra for Ca and K doping are dominated by ions of the dopant atoms and of small dopant clusters as well as by progressions of charged complexes with a number of He atoms [ [8]. The fact that the low Xe k+ charges, k<10, show elevated yields even at high doping pressures > 4 × 10 -3 mbar × cm we attribute to the formation of pure Xe clusters by complete evaporation of the He off the droplets in the course of massive doping and Xe cluster aggregation.…”

Section: Comparison Experiment-simulationmentioning

confidence: 87%

“…The molecular dynamics (MD) simulation method for the interaction of a cluster with the electric and magnetic field of a linearly polarized NIR Gaussian laser pulse was described previously [8,20,21]. All atoms and nanoplasma electrons are treated classically, starting with a cluster of neutral atoms.…”

Section: Simulationsmentioning

confidence: 99%

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Charging dynamics of dopants in helium nanoplasmas

Heidenreich

Grüner

Schomas

et al. 2017

Journal of Modern Optics

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We present a combined experimental and theoretical study of the charging dynamics of helium nanodroplets doped with atoms of different species and irradiated by intense near-infrared (NIR) laser pulses (≤10 15 Wcm -2). In particular, we elucidate the interplay of dopant ionization inducing the ignition of a helium nanoplasma, and the charging of the dopant atoms driven by the ionized helium host. Most efficient nanoplasma ignition and charging is found when doping helium droplets with xenon atoms, in which case high charge states both of helium (He 2+ ) and of xenon (Xe 21+ ) are detected. In contrast, only low charge states of helium and dopants are measured when doping with potassium and calcium atoms. Classical molecular dynamics simulations which include focal averaging generally reproduce the experimental results and provide detailed insights into the correlated charging dynamics of guest and host clusters.

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Ultrafast Dynamics in Helium Droplets

Bruder

Koch

Mudrich

et al. 2022

Topics in Applied Physics

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Helium nanodroplets are peculiar systems, as condensed superfluid entities on the nanoscale, and as vessels for studies of molecules and molecular aggregates and their quantum properties at very low temperature. For both aspects, the dynamics upon the interaction with light is fundamental for understanding the properties of the systems. In this chapter we focus on time-resolved experiments in order to study ultrafast dynamics in neat as well as doped helium nanodroplets. Recent experimental approaches are reviewed, ranging from time-correlated photon detection to femtosecond pump-probe photoelectron and photoion spectroscopy, coherent multidimensional spectroscopy as well as applications of strong laser fields and novel, extreme ultraviolet light sources. The experiments examined in more detail investigate the dynamics of atomic and molecular dopants, including coherent wave packet dynamics and long-lived vibrational coherences of molecules attached to and immersed inside helium droplets. Furthermore, the dynamics of highly-excited helium droplets including interatomic Coulombic decay and nanoplasma states are discussed. Finally, an outlook concludes on the perspectives of time-resolved experiments with helium droplets, including recent options provided by new radiation sources of femto- or even attosecond laser pulses up to the soft X-ray range.

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Efficiency of dopant-induced ignition of helium nanoplasmas

Cited by 25 publications

References 47 publications

Dopant-induced ignition of helium nanoplasmas—a mechanistic study

Dopant-induced ignition of helium nanoplasmas—a mechanistic study

Charging dynamics of dopants in helium nanoplasmas

Ultrafast Dynamics in Helium Droplets

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