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Optimizing impulsive X-ray Raman scattering for population transfer in atomic systems

Impulsive X-ray Raman excitations of Lithium, Neon, and Sodium are calculated using the Multiconfiguration Time-Dependent Hartree-Fock method. Using linearly polarized laser pulses without chirp, we determine the optimum central frequency, intensity, and duration for maximum population transfer to valence excited states. We demonstrate the existence of two local optima or "sweet spots" for population transfer, either of which, depending on the system, may be superior. For some systems we find that population transfer can be maximized by nonresonant Raman transitions, red-detuned below K-edge, because such detuning minimizes core-excited populations and ionization loss. For instance, in Neon near the K-edge the global optimum for population transfer occurs at high intensity (8 $\times$ 10$^{19}$ W cm$^{-2}$), short duration (82as full-width-at-half-maximum), and 24eV red-detuned from the K-edge.