Optical excitation of ultra-relativistic partially stripped ions

Article
Report number	arXiv:2106.00330 ; CERN-PBC-Notes-2021-012
Title	Optical excitation of ultra-relativistic partially stripped ions
Author(s)	Bieroń, Jacek (Jagiellonian U.) ; Krasny, Mieczyslaw Witold (Paris U., VI-VII ; CERN) ; Placzek, Wieslaw (Jagiellonian U.) ; Pustelny, Szymon (Jagiellonian U.)
Publication	Wiley, 2022-02-12
Imprint	2021-06-01
Number of pages	13
Note	Ann. Phys. 534, 2100250 (2022)
In:	Ann. Phys. (Leipzig) 534 (2022) 2100250
DOI	10.1002/andp.202100250 (publication)
Subject category	hep-ex ; Particle Physics - Experiment ; physics.atom-ph ; Other Fields of Physics
Study	CERN Gamma Factory
Project	Gamma Factory
Abstract	The Gamma Factory (GF) initiative aims at the construction of a unique experimental tool exploiting resonant interaction of light with ultra-relativistic partially stripped ions (PSI) stored in circular accelerators at CERN. Resonant excitation of high-energy electronic transitions in the ions is achieved through Doppler-boosting (by twice the Lorentz factor; from hundred to several thousand times) of light energy. In order to efficiently excite the ions, and hence generate intense beams of scattered/fluorescent photons, a detailed knowledge of the ions' electronic energy structure and the dynamics of optical excitation is required. Spectroscopic properties of PSI selected for the GF operation, as well as their optical excitation schemes, are investigated. Two regimes of the ion--light interaction are identified, leading to different dynamics of the excitation. The efficiency of the ion--light interaction, as well as the number of photons emitted from a single ion bunch, are estimated, both analytically and numerically, for three ions considered for the GF, i.e. Li-like ${}^{208}_{\phantom{0}82}$Pb$^{79+}$, Li-like ${}^{40}_{20}$Ca$^{17+}$, and H-like ${}^{208}_{\phantom{0}82}$Pb$^{81+}$.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) publication: © 2022 The Authors. Annalen der Physik published by Wiley-VCHGmbH. (License: CC-BY-4.0)

$The steady-state excited-state population $\rho_{ee}$, determining the fluorescence of the PSI illuminated with light, versus the saturation parameter $\kappa_1$ for three different normalized detunings: $\Delta\tilde\omega=0$ (red), $\Delta\tilde\omega=1$ (green) and $\Delta\tilde\omega=-5$ (blue).$ $Schematics of spectral characteristics of the system. The red line shows the probability of excitation of the motionless PSI. In a weak-light regime, the probability is given by the Lorentz function whose full width at half maximum (FWHM) is determined by the excited-state relaxation rate $\gamma_e$. The middle orange line corresponds to the spectral profile of the pulse used for the excitation, where shading indicates the frequency range that can be used for the ion excitation. The broadest profile corresponds to the transition line inhomogeneously broadened due to the Doppler effect.$ $(Left) The excited-state population of the PSI interacting with the Gaussian light pulse (red trace) of a spectral width coinciding with the atoms' Doppler profile, $\gamma_p^{\rm IRF}=\sigma_\omega^{\rm IRF}$. Different traces corresponds to different detunings of the light central frequency $\omega$ from the Doppler-shifted resonance frequency: $\Delta\omega/\sigma_\omega^{\rm IRF}=0$ (blue), $\Delta\omega/\sigma_\omega^{\rm IRF}=0.5$ (yellow) and $\Delta\omega/\sigma_\omega^{\rm IRF}=1$ (green). (Right) The population of the excited states after the pulse (blue dots) along with the number of the PSI in a specific velocity class (red line) versus the normalized detuning. The results indicate that the PSI-distribution averaged population of the exited state is 70\%. The simulations were performed for the pulse spectrally covering the whole inhomogeneously broadened spectral line and the amplitude of the pulse $\Omega_R^0\approx18000\,\gamma_e$.$ Show more plots

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