P. Hakel

X-ray line polarization spectroscopy of He-like Si satellite line spectra

Laser-produced plasmas driven by high-intensity, femtosecond-duration pulsed lasers have been recognized as sources of short-duration x-ray line emissions. Electron kinetics simulations of such transient and nonequilibrium plasmas predict non-Maxwellian electron distributions and even the presence of electron beams. X-ray line polarization spectroscopy is a diagnostic that can be used to study the directionality of the electron distribution function and thus test electron kinetics simulation results. To this end, we use a time-dependent, collisional-radiative atomic kinetics model of magnetic sublevels to understand the underlying processes and mechanisms leading to the formation of polarized x-ray line emission in Si plasmas driven by high-intensity, ultrashort duration pulsed lasers. We focus on the polarization properties of the He-like Si satellites of the Lyα line. In the cases under consideration, the relevant line emissions last less than 1 ps during which the plasma undergoes a rapid development. ...

Polarization Spectroscopy Modeling With The Inclusion Of Radiation Transport

In the past we have modeled and studied the properties of plasma X‐ray line emissions separately focusing on two features of observed radiation. First, we modeled the polarization properties of He‐like Fe resonance lines in EBIT experiments [1] and of Li‐like and He‐like Si satellite lines in laser‐produced plasmas [2, 3]. These calculations were performed in the optically thin approximation. Second, we modeled and analyzed Al X‐ray line spectra recorded in experiments with targets irradiated by high‐intensity, sub‐picosecond‐duration laser pulses [4, 5]. These experimental spectra were recorded as not polarized; on the other hand, however, we showed the importance of opacity effects on the formation of resonance lines from the He‐like and H‐like ions by performing spectroscopic‐quality radiation‐transport calculations. In the present work we combine the two aspects by adding the consideration of opacity effects into our collisional‐radiative magnetic‐sublevel atomic kinetics model for calculating the pol...

Hot solid-state aluminum plasmas, positrons, and neutrons generated with the garching laser facility ATLAS

We report on time-integrated and time-resolved measurements of the K-shell emission from aluminum plasmas at solid-state density isochorically heated with 2-ω ATLAS pulse of high contrast. We compare the measured spectra with simulated ones. We investigate both plane aluminum and layered targets. The latter consist of a top carbon layer upon an aluminum layer of variable thickness deposited on a sigradur (glass:like carbon) substrate. The layered targets are well suited to study electron beam transport through an overdense plasma. In a different type of experiment, we have produced 106 positrons per laser shot by the interaction of an MeV-electron jet emerging from a relativistically self-focused laser channel in an underdense helium plasma whose density is close to the critical one using a 2-mm thick lead disk. We report about details of the measurement and discuss the propsects of this new table-top positron source for a variety of applications when near-future laser systems are envisaged as a driver. F...