Coulomb driven energy boost of heavy ions for laser plasma acceleration

An unprecedented increase of kinetic energy of laser accelerated heavy ions is demonstrated. Ultra thin gold foils have been irradiated by an ultra short laser pulse at an intensity of $6\times 10^{19}$ W/cm$^{2}$. Highly charged gold ions with kinetic energies up to $> 200$ MeV and a bandwidth limited energy distribution have been reached by using $1.3$ Joule laser energy on target. $1$D and $2$D Particle in Cell simulations show how a spatial dependence on the ions ionization leads to an enhancement of the accelerating electrical field. Our theoretical model considers a varying charge density along the target normal and is capable of explaining the energy boost of highly charged ions, leading to a higher efficiency in laser acceleration of heavy ions

Energetic beams of negative and neutral hydrogen from intense laser plasma interaction

One of the most striking demonstrations of intermolecular forces is the tension at the surface of liquid n-alkanes. The prediction of surface tension is important in the design of distillation towers, extraction units and tower internals such as bubble caps and trays, since it has a considerable influence on the transfer of mass and energy across interfaces. Surface tension data are needed wherever foaming emulsification, droplet formation or wetting are involved. They are also required in a number of equations for two-phase flow calculations and for determining the flow regime. Petroleum engineers are especially interested in the surface tension in the extraction of crude oil to add surfactants to modify the interfacial properties between crude oil and the geological reservoir to improve production and increase oil yields. In this work, a simple computer program using Arrhenius-type asymptotic exponential function, Vandermoned matrix and Matlab technical computing language, is developed for the estimation of surface tension of paraffin hydrocarbons as a function of molecular weight and temperature. The surface tension is calculated for temperatures in the range of 250 to 440 K and paraffin hydrocarbons molecular weights between 30 and 250. The proposed numerical technique is superior owing to its accuracy and clear numerical background, wherein the relevant coefficients can be retuned quickly if more data become available in the future. Estimations are found to be in excellent agreement with the reliable data in the literature with average absolute deviation being less than 2%

Towards understanding excited state properties of organic molecules using time resolved soft X ray absorption spectroscopy

The extension of the pump probe approach known from UV VIS spectroscopy to very short wavelengths together with advanced simulation techniques allows a detailed analysis of excited state dynamics in organic molecules or biomolecular structures on a nanosecond to femtosecond time level. Optical pump soft X ray probe spectroscopy is a relatively new approach to detect and characterize optically dark states in organic molecules, exciton dynamics or transient ligand to metal charge transfer states. In this paper, we describe two experimental setups for transient soft X ray absorption spectroscopy based on an LPP emitting picosecond and sub nanosecond soft X ray pulses in the photon energy range between 50 and 1500 eV. We apply these setups for near edge X ray absorption fine structure NEXAFS investigations of thin films of a metal free porphyrin, an aggregate forming carbocyanine and a nickel oxide molecule. NEXAFS investigations have been carried out at the carbon, nitrogen and oxygen K edge as well as on the Ni L edge. From time resolved NEXAFS carbon, K edge measurements of the metal free porphyrin first insights into a long lived trap state are gained. Our findings are discussed and compared with density functional theory calculation

Ultrafast NEXAFS spectroscopy in the lab using laser based sources and advanced X ray optics

Laboratory based laser driven short pulse X ray sources like laser produced plasmas LPP and high harmonic generation HHG exhibit a great potential for spectroscopy in the soft X ray range. These sources are complementary to large scale facilities like synchrotrons or free electron lasers. For applications of LPP or HHG sources for time resolved X ray absorption spectroscopy in the water window or beyond a high photon flux is crucial. The available photon flux strongly depends on energy, pulse duration and repetition rate of the pump laser. Depending on the experimental needs in time resolved experiments pulse durations of the X ray pulse ranging from nanoseconds to sub femtoseconds are required. In our contribution we will present a highly brilliant LPP source emitting soft X rays in the photon energy range between 50 and 1500 eV based on CPA and thin disk laser technology as well as the high average power thin disk laser based OPCPA system for high photon flux HHG. In addition we present a new generation of reflection zone plates on spherical substrates, that promises a remarkable high resolution over a wide spectral range making it an ideal and highly efficient diffractive optic for time resolved NEXAFS experiments in the la

Parametric study of cycle modulation in laser driven ion beams and acceleration field retrieval at femtosecond timescale

High-frequency modulations appearing in the kinetic energy distribution of laser-accelerated ions are proposed for retrieving the acceleration field dynamics at the femtosecond timescale. Such an approach becomes possible if the laser-cycling field modulates the particle density in the ion spectra and produces quasitime stamps for analysis. We investigate target and laser parameters determining this effect and discuss the dependencies of the observed modulation. Our findings refine a basic mechanism, the target normal sheath acceleration, where an intense and ultrafast laser pulse produces a very strong electrical field at a plasma-vacuum interface. The field decays rapidly due to energy dissipation and forms a characteristic spectrum of fast ions streaming away from the interface. We show that the derived decay function of the field is in accordance with model predictions of the accelerating field structure. Our findings are supported by two-dimensional particle-in-cell simulations. The knowledge of the femtosecond field dynamics helps to rerate optimization strategies for laser ion acceleration