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We put forward a concrete experimental setup allowing to measure light-by-light scattering in the collision of two optical high-intensity laser beams at state-of-the-art high-field facilities operating petawatt class laser systems. Our setup uses the same focusing optics for both laser beams to be collided and employs a dark-field approach for the detection of the single-photon-level nonlinear quantum vacuum response in the presence of a large background. Based on an advanced modeling of the colliding laser fields, we in particular provide reliable estimates for the prospective numbers of signal photons scattered into the dark-field for various laser polarizations., Comment: 26 pages, 5 figures; matches accepted journal version

The Centre for Advanced Laser Applications (CALA) in Garching near Munich features the ATLAS 3000 laser system, which can deliver up to 3\,PW within a pulse length of 20\,fs. It is the driver for the Laser-driven ION (LION) beamline, which aims to accelerate protons and carbons for applications. For commissioning, we currently operate with 5\,J on target in 28\,fs. A $20\degree$ off-axis parabolic mirror focuses the 28\,cm diameter laser-beam down to a micrometer-sized spot, where a vacuum-compatible wave-front sensor is used in combination with a deformable mirror for focus optimization. The nano-Foil Target Positioning System (nFTPS) can replace targets with a repetition rate of up to 0.5\,Hz and store up to 19 different target foils. A dipole magnet in a wide-angle spectrometer configuration deflects ions onto a CMOS detector for an online read-out. Commissioning started mid 2019 with regular proton acceleration using nm-thin plastic foils as targets. Since then proton cut-off energies above 20\,MeV have been regularly achieved. The amount of light traveling backwards from the experiment into the laser is constantly monitored and 5\,J on target have been determined as the current limit to prevent damage in the laser. Protons with a kinetic energy of 12\,MeV are stably accelerated with the given laser parameters and are suitable for transport with permanent magnet quadrupoles towards our application platform. We have performed parameter scans varying target thicknesses to optimize for highest and most stable proton numbers at 12\,MeV kinetic energy, and investigated shot-to-shot particle number stability for the best parameters., Comment: Proceedings to the SPIE Optics + Optoelectronics 2021

High power short pulse lasers provide a promising route to study the strong field effects of the quantum vacuum, for example by direct photon-photon scattering in the all-optical regime. Theoretical predictions based on realistic laser parameters achievable today or in the near future predict scattering of a few photons with colliding Petawatt laser pulses, requiring single photon sensitive detection schemes and very good spatio-temporal filtering and background suppression. In this article, we present experimental investigations of this photon background by employing only a single high power laser pulse tightly focused in residual gas of a vacuum chamber. The focal region was imaged onto a single-photon sensitive, time gated camera. As no detectable quantum vacuum signature was expected in our case, the setup allowed for characterization and first mitigation of background contributions. For the setup employed, scattering off surfaces of imperfect optics dominated below residual gas pressures of $1\times 10^{-4}$ mbar. Extrapolation of the findings to intensities relevant for photon-photon scattering studies is discussed., Comment: 18 pages, 8 figures

Single-shot laser-induced damage threshold (LIDT) measurements of multi-type free-standing ultrathin foils were performed in vacuum environment for 800 nm laser pulses with durations {\tau} ranging from 50 fs to 200 ps. Results show that the laser damage threshold fluences (DTFs) of the ultrathin foils are significantly lower than those of corresponding bulk materials. Wide band gap dielectric targets such as SiN and formvar have larger DTFs than those of semiconductive and conductive targets by 1-3 orders of magnitude depending on the pulse duration. The damage mechanisms for different types of targets are studied. Based on the measurement, the constrain of the LIDTs on the laser contrast is discussed.

The maximum energy loss (Bragg peak) located near the end of range is a characteristic feature of ion stopping in matter, which generates an acoustic pulse, if ions are deposited into a medium in adequately short bunches. This so-called ionoacoustic effect has been studied for decades, mainly for astrophysical applications, and it has recently found renewed interest in proton therapy for precise range measurements in tissue. After detailed preparatory studies with 20 MeV protons at the MLL tandem accelerator, ionoacoustic range measurements were performed in water at the upgraded SIS18 synchrotron of GSI with 238U and 124Xe ion beams of energy about 300 MeV/u, and 12C ions of energy about 200 MeV/u using fast beam extraction to get 1 microsecond pulse lengths. Acoustic signals were recorded in axial geometry by standard piezo-based transducers at a 500 kHz mean frequency and evaluated in both the time and frequency domains. The resulting ranges for the different ions and energies were found to agree with Geant4 simulations as well as previous measurements to better than 1%. Given the high accuracy provided by ionoacoustic range measurements in water and their relative simplicity, we propose this new method for stopping power measurements for heavy ions at GeV energies and above. Our experimental results clearly demonstrate the potential of an ionoacoustic particle monitor especially for very intense heavy ion beams foreseen at future accelerator facilities., Comment: 22 pages, 15 figures, 3 tables, submitted to Nucl Instr Meth A

Today's high-power laser systems are capable of reaching photon intensities up to $10^{22}$ W/cm^2, generating plasmas when interacting with material. The high intensity and ultrashort laser pulse duration (fs) make direct observation of plasma dynamics a challenging task. In the field of laser-plasma physics and especially for the acceleration of ions, the spatio-temporal intensity distribution is one of the most critical aspects. We describe a novel method based on a single-shot (i.e. single laser pulse) chirped probing scheme, taking nine sequential frames at framerates up to THz. This technique, to which we refer as temporally resolved intensity contouring (TRIC) enables single-shot measurement of laser-plasma dynamics. Using TRIC, we demonstrate the reconstruction of the complete spatio-temporal intensity distribution of a high-power laser pulse in the focal plane at full pulse energy with sub picosecond resolution., Comment: Daniel Haffa, Jianhui Bin and Martin Speicher are corresponding authors

The shape of a wave carries all information about the spatial and temporal structure of its source, given that the medium and its properties are known. Most modern imaging methods seek to utilize this nature of waves originating from Huygens' principle. We discuss the retrieval of the complete kinetic energy distribution from the acoustic trace that is recorded when a short ion bunch deposits its energy in water. This novel method, which we refer to as Ion-Bunch Energy Acoustic Tracing (I-BEAT), is a generalization of the ionoacoustic approach. Featuring compactness, simple operation, indestructibility and high dynamic ranges in energy and intensity, I-BEAT is a promising approach to meet the needs of petawatt-class laser-based ion accelerators. With its capability of completely monitoring a single, focused proton bunch with prompt readout it, is expected to have particular impact for experiments and applications using ultrashort ion bunches in high flux regimes. We demonstrate its functionality using it with two laser-driven ion sources for quantitative determination of the kinetic energy distribution of single, focused proton bunches., Comment: Paper: 17 Pages, 3 figures Supplementary Material 16 pages, 7 figures