Optical control of resonant Auger processes

We theoretically show that core-excited-state populations can be efficiently manipulated with strong optical fields during their decay, which takes place in a few femtoseconds. We focus on the $1s^{-1}3p$ resonant excitation in neon, where the $1s^{-1}3p$ and $1s^{-1}3s$ core-excited states are coupled by an optical field. By analyzing the Auger electron spectrum we observe the inner-shell population transfer induced by the optical coupling. We also show that the angular anisotropy of the Auger electron is imprinted in the multipeak structure induced by the optical-dressed continuum, namely sidebands.

Figure 1

(a) Resonant Auger process: A core electron is excited to an unoccupied Rydberg orbital generating a core-excited state with an inner-shell hole, which mainly decays by emitting an electron, namely an Auger electron. (b) Resonant Auger process under an optical field: The optical laser field dresses the continuum and may couple resonantly two outer-shell Rydberg orbitals.

Figure 2

(a) Angle-integrated Auger electron spectrum for the final ion state $2p^{-2}{(}^{1}D)3p$ with the three multiplets ${}^{2}P$, ${}^{2}D$, and ${}^{2}F$. The notation 3p ave. stands for the average of the three multiplets (see more details in Appendix C). (b) Angular distributions of the multiplets with respect to the polarization axis of the x rays (PA). (c) Auger electron spectrum at angles $\theta =0^{\circ }$ and $\theta ={90}^{\circ }$.

Figure 3

(a) Evolution of the ground-state population ($|a_0{\left(t\right)|}^2$). (b) Evolution of the population of the core-excited states $1s^{-1}3p$ and $1s^{-1}3s$ ($|a_1{\left(t\right)|}^2$ and $|a_2{\left(t\right)|}^2$). (c) Angle-integrated Auger electron spectrum in the presence of an optical field; see text for more details.

Figure 4

(a) Angle-integrated Auger electron spectrum for $i=P,D,F$ and $3s$ channels. (b) As (a) but for a smaller energy range showing the envelope for the sidebands corresponding to the ${}^{2}P$ (solid line) and ${}^{2}D$ (dash line) terms. The inset shows the Auger spectrum measured at $\theta ={90}^{\circ }$, with (black line) and without (red line) optical field.

Figure 5

X-ray photoabsorption cross section near the $1s\to 1s^{-1}3p$ resonance for an 800 nm optical field with intensity $5\times {10}^{11}$ W/cm${}^2$. Blue points, numerical results from the ab initio calculations [34]. Solid red line, results from the fitting using Eq. (2) of Ref. [5].