Electron-nucleus interaction in laser fields: The laser-assisted internal conversion process

Abstract

We present a general formalism for an efficient treatment of a broad range of electron-nucleus laser processes. The interaction with the laser beam is taken into account by transforming the system into an oscillating frame, called the Henneberger picture. General expressions for the transition probability per unit time are given in the weak laser field and in the n photonic cases, and connection to previous methods is demonstrated in the appropriate limits. As an example, the transition probability per unit time of laser-induced internal conversion (IC) processes is presented. The conservation of angular momentum in the multiphoton process can be traced well in our calculation. Numerical values of the IC coefficient of the energetically forbidden IC process in case of ${}^{99m}\mathrm{Tc}$ ignited by the absorption of up to three soft-x-ray laser photons are also given. The increase in the rate of IC decay is found comparable to or greater than the natural decay rate of the isomer in case of appropriate intensity and photon energy of the laser. Hard UV laser-induced internal conversion coefficients (ICCs) are also calculated for energetically forbidden shells of ${}^{107}{\mathrm{Ag}}^{m}$ $(K$ shell, $E3,$ $25.47 \mathrm{keV}),$ ${}^{90}{\mathrm{Nb}}^{m}$ ${(L}_{2}$ shell, $M2+E3,$ $2.3 \mathrm{keV}),$ ${}^{183}{\mathrm{W}}^{m}$ ${(N}_{1}$ shell, $E1,$ $544 \mathrm{eV}$ and ${M}_{5}$ shell, $E2,$ $1.79 \mathrm{keV}),$ ${}^{188}{\mathrm{Re}}^{m}$ ${(M}_{2}$ shell, $M3+E4,$ $2.63 \mathrm{keV}),$ ${}^{205}{\mathrm{Pb}}^{m}$ ${(M}_{5}$ shell, $E2,$ $2.4 \mathrm{keV}),$ and ${}^{235}{\mathrm{U}}^{m}$ ${(O}_{4}$ and ${O}_{5}$ shells, $E3,$ $73.5 \mathrm{eV}).$ Measurable induced ICCs are found in case of available intensities and photon energies of the laser beam for the above isomers. Experiments, that may demonstrate the effect and may be tools for determination of nuclear transition energies, are also suggested.