This PDF file contains the front matter associated with SPIE Proceedings Volume 12583, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Modern laser-based accelerators for ions reach peak kinetic ion energies of > 100MeV, over 1MA of total beam currents with only a few picoseconds of bunch duration in close vicinity to the target at ≈ 1 Hz repetition rate and with a high controllability. Thus, the number of potential applications is growing rapidly. This raises a high interest in the processes of ion-matter-interactions in the energy deposition region of these ultra-intense particle bunches. In our recent experiments we investigated these interactions by single-shot time-resolved optical streaking of the energy deposition region of laser-accelerated proton bunches in liquid water. The absolute timing reference provided by the x-rays emitted from the laser-plasma-interaction and the sub-ps time resolution revealed that ionized electrons solvate > 20 ps delayed compared to experiments with lower deposited energy density. In this paper we discuss first approaches to explain these observations by micro-dosimetric considerations regarding the background molecules excitation of vibration states and polarization. This is highly relevant for applications, e.g. to understand the FLASH-effect in radio-biology. We further present the planned experiments at the Centre for Advanced Laser Applications where these phenomena will be investigated in more detail with advanced diagnostics.

Non-destructive material characterization exploiting radiation sources is of crucial importance in several fields ranging from the characterization of artworks to environmental monitoring. For instance, Ion Beam Analysis techniques exploiting particle accelerators stand for their unparalleled detection capabilities. However, the wide use of these techniques is limited by the large costs and dimensions of the exploited sources. In this framework, laser-driven particle acceleration represents a promising alternative to conventional sources since it can address some of their limitations. It relies on the interaction of a super-intense ultrashort laser pulse with a target material to accelerate high-energy electrons and ion bunches. Laser-driven radiation sources are potentially more compact and cheaper than particle accelerators. Moreover, the same laser source can provide different radiations by acting on the target configuration. Besides electrons and ions, high-energy photons and neutrons can be produced by exploiting suitable converter materials. Lastly, the particle energies can be controlled by tuning both the laser intensity and target properties. Here, we show some of the most recent results related to the application of laser-driven radiation sources to materials characterization. Our strategy is based on advanced near-critical Double-Layer Targets (DLT) to enhance the acceleration process. By means of experimental and numerical tools, we show how laser-driven protons, electrons, photons, and neutrons can be exploited for surface and bulk elemental analysis, as well as radiography. Notably, DLTs allow for satisfying the requirements of the techniques, in terms of energies and fluxes, with reduced laser requirements.

A major challenge facing the study of radiation in matter on ultrafast time scales is the need for an absolute timing reference. Typically, these type of experiments are performed using pulses of ions from radio frequency accelerators which have nanosecond scale pulse durations and timing jitter making high temporal resolution measurements difficult to achieve. Here, we show that a combination of a highly synchronised probe pulse with a muti-species laser-driven radiation source can allow for the absolute timing of radiation in matter. This is primarily due to the generation of a X-ray calibration fiducial enabling the study of ion-induced dynamics in matter on ultrafast timescales.

The new short focal length experimental beamline at the BELLA PW, called iP2, was commissioned up to 17 J laser pulse energy, corresponding to a peak intensity of 1.2 × 10²¹ W/cm² on target, based on a measured focal spot size with FWHM 2.7 μm and Gaussian equivalent pulse length of 40 fs. The ion acceleration performance was measured under variation of the laser pulse energy and length, and the laser spot size on target. A maximum proton energy of ∼ 40 MeV was observed in the target normal sheath acceleration regime using 13 μm thick Kapton foil targets. Surveys outside the radiation shielded accelerator cave showed very low radiation levels and there was no measurable activation of experimental installations after performing several tens of shots on target. Back reflections of the laser pulse from the target interaction were monitored and partially mitigated, but ultimately caused damage in the laser frontend. This prohibited further increase of the laser pulse energy beyond 17 J. Implementation of a double plasma mirror is expected to sufficiently suppress back reflections to allow for iP2 experiments at the full BELLA PW pulse energy.

Laser Plasma Accelerators (LPAs), reaching gigavolt-per-centimeter accelerating fields, can generate high peak current, low emittance and GeV class electron beams that can be qualified by a Free Electron Laser (FEL) application. We report here on the commissioning of the COXINEL beamline driven by the HZDR plasma accelerator and experimental demonstration of FEL lasing at 270 nm in a seeded configuration. We also present the transport and characterization of LPA based beams using different imaging systems along the beamline. The use of a streak camera and a UV spectrometer enable to align the seed and the electron beam in the temporal, spectral and transverse domains. Furthermore, the appearance of interference fringes, resulting from the interaction between the phase-locked emitted radiation and the seed, confirms longitudinal coherence, representing an essential feature of seeded FELs. These results are comforted by ELEGANT and GENESIS simulations.

Target pre-heating has proven to be beneficial for laser-driven heavy-ion acceleration. As it allows to remove omnipresent carbohydrate surface contaminants, heating can affect the cutoff energy and increase the efficient acceleration of heavy ions as, e.g., required for the novel fission-fusion nuclear reaction scheme where kinetic energies of fissile species around 7 MeV/u are targeted. At the Centre for Advanced Laser Applications in Garching we use a 3W Nd:YAG cw laser to heat the (in our case gold) target foil in order to investigate the dependency of efficient gold ion acceleration on heating parameters. For real-time assessment of the surface temperature the thermal spectrum is measured with a NIR spectrometer to which Planck’s law is fitted.

Publisher's Note: This paper, originally published on 8 June 2023, was replaced with a corrected/revised version on 3 October 2023. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.