Optimum Pump Pulse Duration for X-Ray Ar-Plasma Lasing

Abstract

In plasma-driven X-ray lasers, it is critical to optimize the duration and time delay between pump pulses. In this study, we have done parametric simulations in order to systematically investigate the optimum time configuration of pump pulses. Here, we are mainly interested in soft X-ray lasers created using a Ar target irradiated with laser pulses, which operate at a wavelength λ = 46.9 nm in the 2p 5 3p 1 (J = 0) → 2p 5 3s 1 (J = 1) laser transition. It is shown that the optimum time scale required to achieve Ne-like ions, as well as the time required to generate a population inversion depend on the combined effect of the electron temperature and electron density. The electron density and temperature are respectively a factor of ≈2.1-and ≈5-times higher in the case of a short pulse of 0.1 ps in comparison to a long pulse of 1,000 ps (at a constant fluence). The most effective lasing happens with short pulses with a pulse duration comparable to the total relaxation time from the upper level, namely ∆τ p ≤ 35 ps. Power laws to predict the optimum laser intensity to achieve Ne-like Ar +8 are obtained.

Atomic Structure Calculations and Study of Plasma Parameters of Al-Like Ions

“…Therefore, we discuss only a brief synopsis here. The Dirac-Coulomb Hamiltonian is given by: (1) where α and β are 4ˆ4 Dirac spin matrices, c is the speed of light, V N represents the monopole part of the electron-nucleus Coulomb interaction and the last term denotes Coulomb interaction between the electrons. An Atomic State Function (ASF) interpreting fine structure levels for the N electron system is constructed by the linear combination of symmetrically fitted and appropriate Configuration State Functions (CSFs).…”

“…The configuration state functions γ i are fabricated by the multiplication of one-electron Dirac orbitals. In Equation (2), C i (δ) are the expansion mixing coefficients for each CSFs, which are attained by means of diagonalization of the Dirac-Coulomb Hamiltonian, given in Equation (1). After this, the radial part of the Dirac orbitals and expansion mixing coefficients are both optimized to self-consistency through the Relativistic Self-Consistent Field (RSCF) method.…”

“…[1][2][3][4]. The necessity of highly accurate and consistent plasma parameters required in order to quantify the plasma and for the detailed understanding of the particle confinement, H modes, fusion products, etc., arises from the fact that the accurate and precise measurements of these parameters at superfluous conditions are very cumbersome due to a limited number of experimental techniques.…”