The pepper-pot method is a widely used technique, originally proposed for measuring the emittance of space-charge-dominated electron beams from radio-frequency photoinjectors. With recent advances in producing high-brightness electron beams via laser-wakefield acceleration (LWFA), the method has also been applied to evaluate emittance in this new regime. Here, the limitations of this method for measuring the emittance of LWFA electron beams are investigated, particularly in parameter regimes where the true beam emittance is overestimated. Conducting an experiment at the JETi200 laser system, we measured an upper bound for the geometric beam emittance of (26.2 + 7.3) mu mmrad using the pepper-pot method. This result is consistent with Geant4 Monte Carlo simulations of the pepper-pot diagnostic, with an input beam-emittance parameter that matches both PIC simulations of the laser-plasma accelerator and an independent measurement using the transient optical grating method.

Quantum field theory predicts a nonlinear response of the vacuum to strong electromagnetic fields of macroscopic extent. This fundamental tenet has remained experimentally challenging and is yet to be tested in the laboratory. A particularly distinct signature of the resulting optical activity of the quantum vacuum is vacuum birefringence. This offers an excellent opportunity for a precision test of nonlinear quantum electrodynamics in an uncharted parameter regime. Recently, the operation of the high-intensity laser ReLaX provided by the Helmholtz International Beamline for Extreme Fields (HIBEF) has been inaugurated at the High Energy Density (HED) scientific instrument of the European XFEL. We make the case that this worldwide unique combination of an x-ray free-electron laser and an ultra-intense near-infrared laser together with recent advances in high-precision x-ray polarimetry, refinements of prospective discovery scenarios, and progress in their accurate theoretical modelling have set the stage for performing an actual discovery experiment of quantum vacuum nonlinearity.

The laser-driven generation of relativistic electron beams in plasma and their acceleration to high energies with GV/m-gradients has been successfully demonstrated. Now, it is time to focus on the application of laser-plasma accelerated (LPA) beams. The "Accelerator Technology HElmholtz iNfrAstructure" (ATHENA) of the Helmholtz Association fosters innovative particle accelerators and high-power laser technology. As part of the ATHENAe pillar several different applications driven by LPAs are to be developed, such as a compact FEL, medical imaging and the first realization of LPA-beam injection into a storage ring. The latter endeavour is conducted in close collaboration between Deutsches Elektronen-Synchrotron (DESY), Karlsruhe Institute of Technology (KIT) and Helmholtz Institute Jena (HIJ). In the cSTART project at KIT, a compact storage ring optimized for short bunches and suitable to accept LPA-based electron bunches is in preparation. In this conference contribution we will introduce the 50 MeV LPA-based injector and give an overview about the project goals. The key parameters of the plasma injector will be presented. Finally, the current status of the project will be summarized.

This Technical Design Report presents a detailed description of all aspects of the LUXE (Laser Und XFEL Experiment), an experiment that will combine the high-quality and high-energy electron beam of the European XFEL with a high-intensity laser, to explore the uncharted terrain of strong-field quantum electrodynamics characterised by both high energy and high intensity, reaching the Schwinger field and beyond. The further implications for the search of physics beyond the Standard Model are also discussed.

Important progress has been achieved since the last PRC meeting towards establishing the necessary boundary conditions for enabling the realization of the first axion dark matter experiment with the necessary sensitivity to detect post-inflationary dark matter axions in the mass range around 100μeV. The project strategy has been refined, especially with respect to magnet development and procurement. Some important technological progress has been achieved in terms of development of the prototype booster. Given the necessary support from DESY and the other Madmax institutes, we believe a dark matter axion search experiment with starting date late 2025 is feasible. An important milestone in the timely realization of the project is the completion and operation of the prototype. We hereby ask the PRC to acknowledge the necessity and urgency of the fast implementation of the Madmax prototype. The Madmax collaboration very much appreciates the letter from the DESY Directorate expressing the interest of DESY to host and provide infrastructure and technical support for the iMadmax and Madmax experiments in addition to the current engagement of the group FH-ALPS. We ask the PRC to back this support and encourage DESY to explore options to further exploit DESYs’ expertise for Madmax:

High-order harmonic generation (HHG) through nonlinear interaction of intense laser beams with different systems is a promising source of bright, ultra-short bursts of extreme-ultraviolet radiation. High harmonics arise since the radiation is emitted as a train of attosecond pulses. A key objective is to achieve a single isolated pulse to allow time resolved measurements characterized by these pulses on an attosecond scale. We carried out experiments into JETI200 facility in Jena, Germany in order to characterize the properties of the harmonic radiation generated from a solid surface interaction, with the ultimate goal of employing temporal gating schemes to reduce the attosecond pulse train to a single pulse. The reason this laser is well suited for such experiment is a combination of its high power and the fact it is “quasi”-few-cycle(6.39 cycles) ideal for trying out gating scheme. Single attosecond pulses are possible from JETI200 under Oblique Incidence Condition

Energy coupling during relativistically intense laser-matter interactions is encoded in the attosecond motion of strongly driven electrons at the pre-formed plasma-vacuum boundary. Studying and controlling this motion can reveal details about the microscopic processes that govern a vast array of light-matter interaction physics and applications. These include research areas right at the forefront of extreme laser-plasma science such as laser-driven ion acceleration1, bright attosecond pulse generation2,3 and efficient energy coupling for the generation and study of warm dense matter4. Here we demonstrate attosecond control over the trajectories of relativistic electron bunches formed during such interactions by studying the emission of extreme ultraviolet (XUV) harmonic radiation. We describe how the precise addition of a second laser beam operating at the second harmonic of the driving laser pulse can significantly transform the interaction by modifying the accelerating potential provided by the fundamental frequency to drive strong coherent emission. Numerical particle-in-cell code simulations and experimental observations demonstrate that this modification is extremely sensitive to the relative phase of the two beams and can lead to significant enhancements in the resulting harmonic yield. This work also reveals that the ability to control these extreme interactions with attosecond precision is an essential requirement for generation of ultra-bright, high temporal contrast attosecond radiation for atomic and molecular pump-probe experiments5,6.

Experimental data supported by simulations indicate that the trajectories of relativistic electron bunches can be controlled at the attosecond timescale by precise adjustment of the relative phase in a two-colour field scheme. An enhancement in the harmonic yield is also reported. Energy coupling during relativistically intense laser–matter interactions is encoded in the attosecond motion of strongly driven electrons at the pre-formed plasma–vacuum boundary. Studying and controlling this motion can reveal details about the microscopic processes that govern a vast array of light–matter interaction phenomena, including those at the forefront of extreme laser–plasma science such as laser-driven ion acceleration1, bright attosecond pulse generation2,3 and efficient energy coupling for the generation and study of warm dense matter4. Here we experimentally demonstrate that by precisely adjusting the relative phase of an additional laser beam operating at the second harmonic of the driving laser it is possible to control the trajectories of relativistic electron bunches formed during the interaction with a solid target at the attosecond scale. We observe significant enhancements in the resulting high-harmonic yield, suggesting potential applications for sources of ultra-bright, extreme ultraviolet attosecond radiation to be used in atomic and molecular pump–probe experiments5,6.

We describe a novel method to improve the temporal intensity contrast (TIC) between the main pulse and prepulses in a high-power chirped-pulse amplification (CPA) laser system. Pre- and post-pulses originating from the limited extinction ratio of the polarization gating equipment are suppressed by carefully adjusting the round-trip times of the regenerative amplifiers (RAs) with respect to the oscillator. As a result, leaking pulses from earlier or later round-trips in the RAs are hidden below the temporal shape of the main pulse. The synchronization can easily be controlled by a contrast measurement on a picosecond time scale using a third-order cross-correlator that enables a sub-mm precise adjustment of the cavity lengths. Finally, a method based on spectral interference is introduced that can be used for a fine-adjustment of the cavity lengths for the daily operation, making this new method easy to implement into existing laser systems.

We present the first well-resolved experimental observation of the non-linear formation of a laser-driven plasma wave, its breaking leading to self-injection and acceleration of electrons in the wave's electric field in the regime of “Bubble-acceleration”.

At the Institute of Optics and Quantum Electronics in Jena, Germany, the currently most powerful diode-pumped solid-state laser system with 25-TW peak power Polaris is in operation. In this paper we give an overview about the dispersion management of the chirped pulse amplification in order to minimize the pulse duration and thus to maximize the intensity available for experiments. A detailed description of the stretcher and compressor design with a novel alignment routine is given as well as measurements for the pulse duration and the temporal contrast. The far field measurement of the beam focussed by an off-axis parabola yields a nearly diffraction limited focal spot.