Relaxation of Ne¹⁺ 1s⁰2s²2p⁶np produced by resonant excitation of an ultraintense ultrafast x-ray pulse

The creation and relaxation of double K-hole states 1s⁰2s²2p⁶np (n ≥ 3) of Ne¹⁺ in the interaction with ultraintense ultrafast x-ray pulses are theoretically investigated. The x-ray photon energies are selected so that x-rays first photoionize 1s²2s²2p⁶ of a neon atom to create a single K-hole state of 1s2s²p⁶ of Ne¹⁺, which is further excited resonantly to double K-hole states of 1s⁰2s²2p⁶np (n ≥ 3). A time-dependent rate equation is used to investigate the creation and relaxation processes of 1s⁰2s²2p⁶np, where the primary microscopic atomic processes including photoexcitation, spontaneous radiation, photoionization and Auger decay are considered. The calculated Auger electron energy spectra are compared with recent experimental results, which shows good agreement. The relative intensity of Auger electrons is very sensitive to the photon energy and bandwidth of x-ray pulses, which could be used as a diagnostic tool for x-ray free electron laser and atom experiments.