Time-resolved study of holeboring in realistic experimental conditions.

The evolution of dense plasmas prior to the arrival of the peak of the laser irradiation is critical to understanding relativistic laser plasma interactions. The spectral properties of a reflected laser pulse after the interaction with a plasma can be used to gain insights about the interaction itself, whereas the effect of holeboring has a predominant role. Here we developed an analytical model, describing the non-relativistic temporal evolution of the holeboring velocity in the presence of an arbitrary overdense plasma density and laser intensity profile. We verify this using two-dimensional particle-in-cell simulations, showing a major influence on the holeboring dynamic depending on the density profile. The influence on the reflected laser pulse has been verified during an experiment at the PHELIX laser. We show that this enables the possibility to determine the sub-micrometer scale length of the preplasma by measuring the maximum holeboring velocity and acceleration during the laser-plasma interaction.

Alignment procedure for off-axis-parabolic telescopes in the context of high-intensity laser beam transport.

Off-axis parabolic telescopes are rarely used in high-intensity, high-energy lasers, despite their favorable properties for beam transport such as achromatism, low aberrations and the ability to handle high peak intensities. One of the major reasons for this is the alignment procedure which is commonly viewed as complicated and time consuming. In this article, we revisit off-axis parabolic telescopes in the context of beam transport in high-intensity laser systems and present a corresponding analytical model. Based on that, we propose a suitable setup that enables fast and repeatable alignment for everyday operation.

Experimental discrimination of ion stopping models near the Bragg peak in highly ionized matter.

The energy deposition of ions in dense plasmas is a key process in inertial confinement fusion that determines the α-particle heating expected to trigger a burn wave in the hydrogen pellet and resulting in high thermonuclear gain. However, measurements of ion stopping in plasmas are scarce and mostly restricted to high ion velocities where theory agrees with the data. Here, we report experimental data at low projectile velocities near the Bragg peak, where the stopping force reaches its maximum. This parameter range features the largest theoretical uncertainties and conclusive data are missing until today. The precision of our measurements, combined with a reliable knowledge of the plasma parameters, allows to disprove several standard models for the stopping power for beam velocities typically encountered in inertial fusion. On the other hand, our data support theories that include a detailed treatment of strong ion-electron collisions.