[en] Today's most intense light fields that can be produced in a laboratory are generated within the focus of high-intensity laser pulses. These fields of up to 10¹² V/cm are able to ionize light elements down to the bare nucleus by field-ionization. During the interaction of an intense laser pulse with solid matter not only field-ionization but also collisional heating leads to the generation of a hot and dense plasma. A high-intensity laser, exceeding 10¹⁸ W/cm², interacting with this plasma accelerates electrons up to relativistic energies. In the remaining solid target material these electrons are decelerated, generating brilliant x-ray line radiation as well as short-pulsed bremsstrahlung with energies up to a few hundreds of megaelectronvolts. This work deals with the generation of such laser based high energy x-ray radiation.The dependence on laser intensity of the generation of K_α-radiation at relativistic intensities is discussed. Secondly, hard bremsstrahlung emission is used to induce nuclear reactions and to measure a photo reaction cross section in ¹²⁹I. These experiments are only feasible with very high laser intensities. Therefore the multi-Terawatt Ti:sapphire laser in Jena has been upgraded to one of the most intense tabletop lasers worldwide. It now routinely delivers pulses of 360 mJ energy within a focal spot area of 5 μm² and a pulse duration of minimum 60 fs. This results in peak intensities of up to 10²⁰ W/cm²

[en] This paper reports on an vitro study performed to examine the ability of current-day radiography for detecting metaphyseal bone loss. A block was cut from the anterior aspect of a cadaveric distal femur, sequential sections (approximately 4% of the BMC of the block) were cut from the block, and a fat-equivalent material was substituted in to the void. Following removal of each bone section, the femur was placed in a water bath, a lateral radiography was taken, and the ash content of the section was determined. Five readers each evaluated over 100 combinations of two radiographs side by side, noting whether there was no difference or whether one femur's region of interest was denser. The readings were compared with bone mineral differences as determined by ashing. All readers identified losses of 25% or more, and 5%-10% losses were seen by four of five readers half of the time

[en] High energy gamma rays, produced via ultra intense laser-gas interactions have been used to induce photo-proton reactions in various materials. The Jena multi-terawatt, (I=5x10''19 W/cm''2, 80 fs) table-top laser is focused into a He gas jet (10''19 cm''-3), generating a relativistic plasma channel, while the stability of the channel formation is monitored with a 2ω probe beam. Electrons in the relativistic channel are accelerated to energies of ∼5-40MeV and have a quasi exponential energy profile with temperatures of the order of 10 MeV. the electrons are incident on a primary converter target (tantalum) og high proton number (z), thus generating high energy Bremsstrahlung photons, which can induce (γ, n) and (γ, p) reactions in a secondary target. Specifically, secondary targets of various z (magnesium, titanium, zinc and molybdenum) have been investigated, to compare the ratios of (γ, p) and (γ, n) reactions as a function of z. Photonuclear data describing the interaction of photons with atomic nuclei are of great importance for a variety of applications, such as radiation shielding, radiotherapy and possible transmutation studies. While the majority of work carrie out using both conventional nuclear techniques and laser plasma produced photons has looked at photo-neutron reactions, it has been highlighted that the charged particle emission is as important, especially in the low z range, where the threshold energies and cross sections may be very similar. (Author)

[en] Plasmas are attractive media for the next generation of compact particle accelerators because they can sustain electric fields larger than those in conventional accelerators by three orders of magnitude. However, until now, plasma-based accelerators have produced relatively poor quality electron beams even though for most practical applications, high quality beams are required. In particular, beams from laser plasma-based accelerators tend to have a large divergence and very large energy spreads, meaning that different particles travel at different speeds. The combination of these two problems makes it difficult to utilize these beams. Here, we demonstrate the production of high quality and high energy electron beams from laser-plasma interaction: in a distance of 3 mm, a very collimated and quasi-monoenergetic electron beam is emitted with a 0.5 nanocoulomb charge at 170 ± 20 MeV. In this regime, we have observed very nonlinear phenomena, such as self-focusing and temporal self-shortenning down to 10 fs durations. Both phenomena increase the excitation of the wakefield. The laser pulse drives a highly nonlinear wakefield, able to trap and accelerate plasma background electrons to a single energy. We will review the different regimes of electron acceleration and we will show how enhanced performances can be reached with state-of-the-art ultrashort laser systems. Applications such as gamma radiography of such electron beams will also be discussed

No abstract available

[en] Powerful table-top lasers are now available in the laboratory and can be used to induce nuclear reactions. We report the first demonstration of nuclear fission using a high repetition rate table-top laser with intensities of 10²⁰ W/cm². Actinide photo-fission has been achieved in both ²³⁸U and ²³²Th from the high-energy Bremsstrahlung radiation produced by laser acceleration of electrons. The fission products were identified by time-resolved γ-spectroscopy. (authors)

[en] The spatial structure of the Kα emission from Ti targets irradiated with a high intensity femtosecond laser has been studied using a two-dimensional monochromatic imaging technique. For laser intensities I<5x10¹⁷ W/cm², the observed spatial structure of the Kα emission can be explained by the scattering of the hot electrons inside the solid with the help of a hybrid particle-in-cell/Monte Carlo model. By contrast, at the maximum laser intensity I=7x10¹⁸ W/cm² the half-width of the Kα emission was 70 μm compared to a laser-focus half-width of 3 μm. Moreover, the main Kα peak was surrounded by a halo of weak Kα emission with a diameter of 400 μm and the Kα intensity at the source center did not increase with increasing laser intensity. These three features point to the existence of strong self-induced fields, which redirect the hot electrons over the target surface

[en] Fusion neutrons from a heavy water droplet target irradiated with laser pulses of 3x10¹⁹ W/cm² and from a deuterated secondary target are observed by a time-of-flight (TOF) neutron spectrometer. The observed TOF spectrum can be explained by fusion of deuterium ions simultaneously originating from two different sources: ion acceleration in the laser focus by ponderomotively induced charge separation and target-normal sheath acceleration off the target rear surface. The experimental findings agree well with 3D particle-in-cell simulations

[en] We have measured the temporal shortening of an ultraintense laser pulse interacting with an underdense plasma. When interacting with strongly nonlinear plasma waves, the laser pulse is shortened from 38±2 fs to the 10-14 fs level, with a 20% energy efficiency. The laser ponderomotive force excites a wakefield, which, along with relativistic self-phase modulation, broadens the laser spectrum and subsequently compresses the pulse. This mechanism is confirmed by 3D particle in cell simulations

[en] Photo-nuclear reactions were investigated using a high power table-top laser. The laser system at the University of Jena (I ∼ 3-5x10¹⁹ W cm^-2) produced hard bremsstrahlung photons (kT∼2.9 MeV) via a laser-gas interaction which served to induce (γ, p) and (γ, n) reactions in Mg, Ti, Zn and Mo isotopes. Several (γ, p) decay channels were identified using nuclear activation analysis to determine their integral reaction yields. As the laser-generated bremsstrahlung spectra stretches over the energy regime dominated by the giant dipole resonance (GDR), these yield measurements were used in conjunction with theoretical estimates of the resonance energies E_res and their widths Γ_res to derive the integral reaction cross-section σ^int(γ,p) for ²⁵Mn, ^48,49Ti, ⁶⁸Zn and ^97,98Mo isotopes for the first time. This study enabled the determination of the previously unknown σ^int(γ,n)/σ^int(γ,p) cross-section ratios for these isotopes. The experiments were supported by extensive model calculations (Empire) and the results were compared to the Thomas-Reiche-Kuhn (TRK) dipole sum rule as well as to the experimental data in neighboring isotopes and good agreement was observed. The Coulomb barrier and the neutron excess strongly influence the σ^int(γ,n)/σ^int(γ,p) ratios for increasing target proton and neutron numbers