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Quantum Electronics

Pump and amplification dynamics of gamma rays in a nuclear medium with the hidden population inversion

Лев Абрамович Ривлин

Published Dec 31, 2009• 1 citation

Abstract

The features of the pump dynamics of isomeric nuclei excited by X-rays of a repetitively pulsed relativistic electron beam followed by the production of a medium with the negative absorption of gamma quanta are analysed. In the extended nuclear medium, the pump excites a travelling hidden-population-inversion wave with the anisotropic gamma amplification, which becomes positive in the case of the excess over the critical pump parameter equal to the product of the peak spectral power density of the X-ray source and the relative duration of an ultrashort relativistic electron bunch. In the alternative scheme with orthogonal directions of pumping X-rays and a flux of amplified gamma quanta, the absence of the amplification anisotropy opens up the possibility for constructing a standard two-mirror resonator with Bragg single-crystal reflectors. The critical peak value of the spectral pump power density is compared with the known characteristics of relativistic-electron X-ray sources by examples of some nuclides.

DOI: 10.1070/qe2009v039n12abeh014041

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The concept of a γ-ray laser which makes use of the kinematic shift and the splitting of the spectral lines of radiative γ-transitions observed in an ensemble of free nuclei owing to recoil is considered. These effects form a prerequisite for the formation of hidden population inversion with no excess of the number of excited emitters over the number of unexcited ones, for implementation of a broadband unperturbing x-ray pump in an unconventional 'two-level' scheme, for the manifestation of anisotropic quantum amplification without any reflecting structures, etc. These attractive properties offer strong possibilities of staging an initial demonstration nuclear γ-ray laser experiment.

We propose a new scheme of gamma-quanta amplification without inversion. Laser pumping of electron states creates giant nuclear-spin polarisation via the hyperfine interaction. This results in extreme cooling of the ground-state nuclear spin in a projection which does not absorb both laser pump and gamma-quanta according to selection rules for these transitions. Induced emission from the nuclear excited state is not influenced by the pump. Therefore gamma-quanta travelling inside the pump beam have an opportunity to induce stimulated emission without subsequent quenching by ground state nuclei.