Demonstration of quasiresonant x-ray photoexcitation in a laser-created plasma

Resonant photoexcitation in a two-component plasma is demonstrated for the first time in the x-ray range. The 1s-3p resonance line of Al x i i i at 6.053 Å is used to pump the 2${\mathit{p}}^{\mathrm{*}}$ ${(}^1$ ${\mathit{S}}_0$)-2${\mathit{p}}^5$3d ${(}^3$ ${\mathit{D}}_1$) line of Sr x x i x at 6.059 Å. Absorption of the aluminum pump line by the strontium plasma is shown unambiguously. The resulting increase in the x-ray fluorescence intensity of the pumped level is measured in a time-resolved experiment.