OPTICAL SPECTROSCOPY OF LASER PLASMA PRODUCED BY ABLATION OF METAL TARGET IN SUPERFLUID HELIUM Текст научной статьи по специальности «Физика»

OPTICAL SPECTROSCOPY OF LASER PLASMA PRODUCED BY ABLATION OF METAL TARGET IN SUPERFLUID HELIUM

Boltnev R.E.1' 2, Karabulin A.V.1' 3, Krushinskaya I.N.2, Pelmenev A.A.2, and

Matyushenko V.I.2

1 Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, Russia 2 Branch of Semenov Federal Research Center for Chemical Physics, Russian Academy of

Sciences, Chernogolovka, Moscow region, Russia 3 Federal Research Center for Problems of Chemical Physics and Medicinal Chemistry, Russian Academy of Sciences, Chernogolovka, Moscow region, Russia

boltnev@gmail.com

We have analyzed the luminescence spectra of a plasma plume during laser ablation of a metal target immersed in superfluid helium. Appearance of excited helium atoms in plasma reveals the formation of helium ions at the laser power density below the breakdown threshold of liquid helium « 10 GW/cm2 [1]. The main channel for the formation of helium ions in plasma at the laser power density below the breakdown threshold of liquid helium has been determined [2]. It occurs in two steps through the formation of metastable ionic complex of a helium atom and a triply-charged metal ion, M3+ + He ^ HeM3+

followed by the complex dissociation due to its interaction with the neutral metal atom, HeM3+ + M ^ He+ + M2+ + M+ + e.

The helium atom luminescence during ablation of metal targets at the laser power density below the breakdown threshold of liquid helium was observed exclusively for Ni, Co, Ga, Au, and Ag, the metals with a positive balance IE2+ - 24.59 - IE > 0,

where 24.59 eV is the ionization energy of a helium atom, IE and IE2+ are the ionization energies of neutral metal atom under study and its doubly-charged ion, correspondingly. It was shown that the value of IE2+ for a gold atom has to be higher than 34 eV whereas in some reference databases its value is estimated as 30 eV [3].

The maximal temperature inside a laser plume was determined from the line intensities of neutral metal atoms and ions as high as 1.6 eV, while the density of sublimated metal atoms reached ~1018 per cm3.

References

1. Sirisky S., Yang Y., Wei W., Maris H.J. // J. Low Temp. Phys. - 2017. - V. 189. P. 53-59.

2. Boltnev R.E., Karabulin A.V., Krushinskaya I.N., Pelmenev A.A., and Matyushenko V.I. // High Energy Chem. - 2023. - V. 57 -P. 168-174.

3. NIST Atomic Spectra Database, NIST Standard Reference Database 78, https://physics.nist.gov/PhysRefData/ASD/ionEnergy.html