Determination of the Ion Temperature in a Plasma Created by Optical Field Ionization

Abstract

International audienceThe evolution with time of the ion temperature of a xenon gas during and after the irradiation with a high intensity laser beam is determined. The processes taken into account are (i) direct interaction with the laser beam, (ii) binary collisions with hot electrons, (iii) contribution with the electrostatic wakefield, (iv) hydrodynamic expansion and (v) transfer of potential to kinetic energy among the plasma ions. It is shown that, because the ions are strongly coupled, the last process is by far the most efficient one. Using the One Component Plasma (OCP) model, a simple analytical formula for the ion temperature at equilibrium is obtained. Application of this work to the development of soft x-ray laser sources is stressed out

Observation of spectral gain narrowing in a high-order harmonic seeded soft-x-ray amplifier

“…Its FWHM is λ H = 5 mÅ in the case of the 32.8-nm Ni-like laser. The Stark effect has been introduced as a source of inhomogeneous spectral broadening, but numerical simulations have shown that it can be neglected [12]. The main process responsible for inhomogeneous broadening is the ion Doppler effect.…”

“…Ions are indeed rapidly heated after ionization by the laser field. Theoretical investigations [12] have shown that strong correlations exist in OFI plasmas, which rapidly relax into an uncorrelated form with a characteristic time equal to the plasma period (a few hundreds of femtoseconds). The ion equilibrium temperature in the case of our low-density OFI plasma is T i = 6 eV.…”

Fourier-limited seeded soft x-ray laser pulse

“…Simulations with the PPP [10] code show that the ion Stark effect can be neglected. However, a rapid ion heating is following the ionization by the IR laser optical field, because the OFI plasma is produced in a state where important ion correlations exist [11]. The plasma relaxes rapidly in an uncorrelated form after a characteristic time equal to the inverse of the plasma frequency (a few hundreds of femtoseconds).…”

Theoretical and experimental investigations of spectral and temporal properties of seeded soft x-ray lasers

“…Theoretical work have indeed shown that the OFI plasma is in a state were important ion correlation exists. 11 The plasma relaxes rapidly in a uncorrelated form with a characteristic time equal to the plasma period. For the conditions of the OFI laser the temperature reached by the ions after this relaxation is of 6 eV.…”