Model of a Femtosecond X-Ray Laser at 32.8 and 44.4 nm in Ni-Like Krypton

The possibility of creating an efficient X-ray laser in Ni-like krypton based on the conventional 3d5/24d5/2 [J = 0] – 3d3/24p1/2 [J = 1] transition at λ = 32.8 nm and on the transition with optical self-pumping 3d3/24f5/2 [J = 1] – 3d3/24d5/2 [J = 1] at λ = 44.4 nm is predicted for the femtosecond timescale. The plasma filament is excited upon interaction of a jet of krypton clusters with an intense pump laser pulse. Optimal conditions to achieve the duration tlas ≤ 300 fs of the X-ray laser radiation are determined. The optimal electron density is in a rather narrow interval in the range ne ~ 1021 − 2 × 1021 cm−3. The optimal electron temperature is several keV. It is likely that this explains the fact that no X-ray laser has been observed on the self-pumped X-ray laser in Kr8+ so far. For this transition the conversion factor per pulse is found to be ~ 5 × 10–5. For an X-ray laser operating on the conventional transition 3d5/24d5/2 [J = 0] – 3d3/24p1/2 [J = 1] at λ = 32.8 nm, tlas ≤ 300 fs can also be achieved; however, the conversion factor for this transition is times ~ 5 smaller than that for the self-pumped transition.