The enhancement effect of a microstructured surface on laser absorption and characteristic K alpha emission has been investigated by measuring K-shell emission from titanium (Ti) targets irradiated with high-intensity (similar to 1020 W cm-2), subpicosecond (500 fs) laser pulses. The experimental results indicate a modest enhancement (1.6x) of K alpha emission from microstructured targets compared to flat foils, but with a similar intensity and profile of He alpha and Li-like satellites. Particle-in-cell (PIC) simulations are implemented to further understand the underlying physical processes in the laser interaction with both targets, interpreting the mechanisms responsible for the K alpha enhancement. The reasons for the lower-than-expected enhancement of K alpha emission are discussed. The rapid heating of the bulk plasma might result in the premature shutdown of K alpha emission before the thermalization of hot electrons or even the end of laser pulses, suggesting that the use of K alpha emission as a diagnostic of the hot-electron yield or relaxation could lead to a misinterpretation.

High backlighter brightness is important to maximize the number of detected photons in radiography experiments and to minimize the background while back-lighting high-energy-density plasmas with strong self-emission. Several different configurations were tested to improve the brightness of the Si He-alpha x-ray line emission at a photon energy of 1865 eV from high-energy (> 1 kJ), short-pulse (-20 ps), laser-driven backlighter targets. The emission from low-density SiO2 foam targets, the effects of a laser prepulse, and Si targets with a CH "shield " that form a small cavity were compared to solid-density, flat Si targets. The CH "shield " targets showed the best performance with a > 5ximprovement in time-integrated emission and an x-ray pulse duration of similar to 25 ps with no measurable spectral shift of the Si He-alpha emission line. A conversion efficiency from laser light into Si He alpha photons on the order of 1 x 10(-5) was inferred from the data.

We present the usage of two-layer targets with laser-illuminated front-side microstructures for x-ray backlighter applications. The targets consisted of a silicon front layer and copper back side layer. The structured layer was irradiated by the 500-fs PHELIX laser with an intensity above 10^{20}Wcm^{-2}. The total emission and one-dimensional extent of the copper Kα x-ray emission as well as a wide spectral range between 7.9 and 9.0 keV were recorded with an array of crystal spectrometers. The measurements show that the front-side modifications of the silicon in the form of conical microstructures maintain the same peak brightness of the Kα emission as flat copper foils while suppressing the thermal emission background significantly. The observed Kα source sizes can be influenced by tilting the conical microstructures with respect to the laser axis. Overall, the recorded copper Kα photon yields were in the range of 10^{11}sr^{-1}, demonstrating the suitability of these targets for probing applications without subjecting the probed material to additional heating from thermal line emission.

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.