Jens Hartmann

A novel approach to electron data background treatment in an online wide-angle spectrometer for laser-accelerated ion and electron bunches

Laser-based ion acceleration is driven by electrical fields emerging when target electrons absorb laser energy and consecutively leave the target material. A direct correlation between these electrons and the accelerated ions is thus to be expected and predicted by theoretical models. We report on a modified wide-angle spectrometer, allowing the simultaneous characterization of angularly resolved energy distributions of both ions and electrons. Equipped with online pixel detectors, the RadEye1 detectors, the investigation of this correlation gets attainable on a single shot basis. In addition to first insights, we present a novel approach for reliably extracting the primary electron energy distribution from the interfering secondary radiation background. This proves vitally important for quantitative extraction of average electron energies (temperatures) and emitted total charge.

Integrated double-plasma-mirror targets for contrast enhancement in laser ion acceleration

We introduce a target concept for laser-driven ion acceleration with ultrashort, highly intense laser pulses that includes an integrated double plasma mirror for contrast enhancement. It comprises three nanometer thin plastic foils, embedded in a small metal structure, which ensures precise mounting. The geometry allows to apply a double plasma mirror directly in front of a target foil within the converging beam, enabling moderate-energy (~1 J) laser systems to reach the required fluence of several hundred J/cm2 on the plasma mirrors. During an experimental campaign, performed at the Laboratory for Extreme Photonics in Munich, we observed proton energies increased by a factor of three using this new target, which is attributed to an enhanced laser contrast after the integrated double plasma mirrors.

The spatial contrast challenge for intense laser-plasma experiments

Achieving the highest peak intensity possible is a key requirement of a majority of laser-plasma experiments. This requires confining laser energy to a small volume. The experimental determination of the spatial focus distribution is therefore important, especially to connect theoretical and experimental results. In this paper, we revise a new method to evaluate the spatial performance of a laser focus. Obtaining low- and high-dynamic-range (LDR/HDR) images of the laser focus profile is described for a typical high-intensity laser setup, and present data from our case study. We compare standard evaluation procedures based on both images quantitatively and determine the accuracies and associated errors. A spread out intensity distribution below the detection limit of the LDR is observed in the HDR acquisition. Our evaluation reveals that only considering LDR can overestimate the enclosed energy as well as the peak intensity by factors of 1.5. With our method we estimate the required dynamic range for this case to 4 orders of magnitude. Our discussion sheds light on possible causes for the deteriorative effect to targets in the vicinity of the primary focal spot.

Laser interactions with micro-targets for imaging applications

Relativistic laser-plasma interactions as drivers for intense and energetic bursts of proton, electron and photon radiation have been studied for more than a decade [1,2,3]. Much of the attention is driven by their potential use in medical physics, to build compact and affordable sources for diagnostics and therapy. So far, these efforts were focused on single species radiation, meaning either ions, electrons or photons, whilst regarding the respective other species as a disturbance [4,5,6].

Laser-driven ION (LION) acceleration at the centre for advanced laser applications (CALA)

Irradiating thin foils with very intense laser pulses results in the emission of swift ion bunches. These laser-accelerated ions exhibit properties that substantially differ from conventionally accelerated particles. A large number of a variety of ion species distributed over a broad energy and angular spectrum are confined to very short bunch durations and are sought to enable novel applications [1]. For many years these properties have been studied and optimized mainly by investigating the interaction process of intense lasers pulses with plasmas in exemplary experiments [2].

Considerations on employing a PMQ-doublet for narrow and broad proton energy distributions

Abstract We simulated a doublet of permanent magnet quadrupoles (PMQs) to estimate the sensitivity on positioning precision and its impact on the spectral properties of transported protons. The study guided the construction and testing of a focusing setup for laser-accelerated proton bunches with energies between 6 and 10 MeV. Our results shed light on possible applications that may arise from broad input particle spectra.