[en] This cumulative thesis summarizes experimental and theoretical results on cooling of ion beams using single-frequency, single-mode tabletop laser systems. It consists of two parts. One deals with experiments on laser-cooling of ion beams at relativistic energies, the other with simulations of stopping and sympathetic cooling of ions for precision in-trap experiments. In the first part, experimental results are presented on laser-cooling of relativistic C³⁺ ion beams at a beam energy of 122 MeV/u, performed at the Experimental Storage Ring (ESR) at GSI. The main results presented in this thesis include the first attainment of longitudinally space-charge dominated relativistic ion beams using pure laser-cooling. The second part lists theoretical results on stopping and sympathetic cooling of ions in a laser-cooled one-component plasma of singly charged ²⁴Mg ions, which are confined in a three-dimensional harmonic trap potential. (orig.)

[en] In the Travelling-wave Thomson-scattering (TWTS) scheme ultrashort and narrow-band light pulses in the X-Ray region of the spectrum are created by scattering high intensity laser pulses from relativistic electron bunches. TWTS uses lasers with a pulse front tilt in a side-scattering geometry to scale the interaction length into the centimeter to meter range. This is crucial for allowing the scattered radiation to act back on the electrons which eventually can lead to coherent amplification of the radiation as in a free electron laser (FEL). We study the electron dynamics in the laser field including back reaction effects and discuss the applicability of TWTS as a SASE-FEL.

[en] Measuring the transient plasma density structures of Laser-wakefield accelerators (LWFA) that are shorter than the drive laser on a μm-fs-scale is experimentally challenging, which complicates comparisons the of these results with numerical models from 3D-PIC simulations. Radiation spectra from LWFA plasmas on the other hand are straightforward to measure, but hard to calculate in realistic detail because it is computationally expensive (both CPU and memory) to calculate the radiation emitted by a complete PIC simulation. However, it would be very useful to know where to look for ''good'' radiation signatures that show quantitative details on the electron dynamics at electron injection. Here we present a highly-scalable, classical radiation code based on Lienard-Wiechert potentials, which runs on high-performance computing clusters using GPUs. The memory and disk-space footprint is reduced by directly integrating into the 3D-PIC code PicOnGPU. With this new code, it is possible to calculate logarithmic-scaled spectra from IR to X-ray wavelengths in arbitrary observation directions. In this talk we put the emphasis on the code architecture, the verification of the physics and on some first results.

[en] Laser-wakefield accelerators (LWFA) feature electron bunch durations ranging from several fs to tens of fs. Knowledge and control of the electron bunch duration is vital to the design of future table-top, X-ray light-sources for laser-synchronized pump-probe experiments, ranging from betatron radiation, Thomson scattering to FELs. Due to the nonlinear nature of the laser-wakefield electron injection and small changes in initial experimental conditions the electron bunch properties are often subject to large shot-to-shot variations, which requires diagnostics working not only at ultrashort time-scales but also at single-shot. We aim for measurements of the LWFA electron bunch duration and bunch substructure at single-shot by analysing the coherent and incoherent transition radiation spectrum. Our ultra-broadband spectrometer ranges from the UV (200 nm) to the mid-IR (12 μm), which allows to resolve time-scales from 0.7 to 40 fs. The prism and grating-based spectrometer divides and maps the spectrum onto three detector systems (UV/VIS;NIR;MIR) of staggered, increasing resolution towards lower wavelengths. Here we present the experimental approach, scope and current status of our spectrometer project.

[en] The properties of electron bunch based on the Laser-Wakefield accelerators (LWFA) vary from shot to shot due to changes in the environment, such as gas jet profile or laser pointing. In order to understand the properties of these ultra-short electron bunches like bunch duration and bunch substructure in the range of 0.7 to 40 fs we are building a broadband-spectrometer for measuring coherent and incoherent transition radiation (TR). Our TR-spectrometer is able to measure the TR-spectrum from a thin Al-foil in a single shot experiment from UV (200 nm) to mid-IR (12 μm) by means of a CCD detector for the UV to VIS range and two array detectors for the NIR and MIR range. In this poster we present our design and calibration results of the detectors.

[en] Recent laser-ion acceleration experiments performed at the 150 TW Draco laser in Dresden, Germany, have demonstrated the importance of a precise understanding of the electron dynamics in solids on an ultra-short time scale. For example, with ultra-short laser pulses a description based purely on the evolution of a thermal electron ensemble, as in standard TNSA models, is not sufficient anymore. Rather, non-thermal effects during the ultra-short intra-pulse phase of laser-electron interaction in solids become important for the acceleration of ions when the laser pulse duration is in the order of only a few tens of femtoseconds. While the established maximum ion energy scaling in the TNSA regime goes with the square root of the laser intensity, for such ultra short pulse durations the maximum ion energy is found to scale linear with laser intensity, motivating the interest in such laser systems. Investigating the influence of laser pulse contrast, laser polarization and laser incidence angle on the proton maximum energy and angular distribution, we present recent advances in the description of the laser interaction with solids, focusing on the implications of intra-pulse non-thermal phenomena on the ion acceleration.

[en] We present a systematic investigation of ultra-short pulse laser acceleration of protons yielding unprecedented maximum proton energies of 17 MeV using the Ti:Sapphire lased high power laser of 100 TW Draco at the Research Centre Dresden-Rossendorf. For plain few micron thick foil targets a linear scaling of the maximum proton energy with laser power is observed and attributed to the short acceleration period close to the target rear surface. Although excellent laser pulse contrast was available slight deformations of the target rear were found to lead to a predictable shift of the direction of the energetic proton emission away from target normal towards the laser direction. The change of the emission characteristics are compared to analytical modelling and 2D PIC simulations.

[en] Laser prepulses and pedestals can have significant effect on the acceleration of ions during the main pulse. For example, even though the prepulse intensity level usually is some orders of magnitude below that of the main pulse, due to the long timespan between the prepulse and the main pulse this can be sufficient for the plasma to expand significantly. For example, this can cause the laser absorption to increase, the density gradients to faint and the different ion species to separate. We study the plasma dynamics via 2D collisional PIC simulation including several ion species and a dynamic ionization of a realistic target model. We discuss the implications this has for experimental conditions e.g. for ion acceleration from mass limited targets.

[en] Recent experimental results on the filamentation of laser accelerated proton beams at high laser irradiation intensities are compared to particle-in-cell simulations. In simulations, several qualitatively different mechanisms of filamentation of electrons can be observed. Depending on the specific laser and target parameters such as flatness or density, the relative role of individual electron instabilities can be actively controlled. It is demonstrated how filamentation of electron currents going into the target and heating the rear surface can translate into ion filamentation which consequently exhibit strong correlation with the front side laser-electron instability physics. The impact on ion energy scaling are discussed. Experimental observation of proton filamentation can thus be a valuable diagnostics of the laser-electron interaction at the foil front surface. We moreover propose and discuss other more direct techniques for probing spatio-temporal electron density and ionization.

[en] We study the generation of hot electron currents in solid targets that are generated when an ultra-intense laser beam interacts with the solid. Simulations were performed with highly idealized parameters in order to allow direct comparison to existing and new models that often assume idealized conditions. We compare our results with popular existing scaling laws and show for example that the simple scaling j gamma*n_c does not apply, especially when the electron energy is derived from the ponderomotive or similar scalings or when the laser intensity is large. We demonstrate the impact of correctly modeling the hot electron current including its temporal structure on bulk electron heating and finally build a model that is in almost perfect agreement with simulations.