Time-Of-Flight (TOF) methods are very effective to detect particles accelerated in laser-plasma interactions, but they show significant limitations when used in experiments with high energy and intensity lasers, where both high-energy ions and remarkable levels of ElectroMagnetic Pulses (EMPs) in the radiofrequency-microwave range are generated. Here we describe a novel advanced diagnostic method for the characterization of protons accelerated by intense matter interactions with high-energy and high-intensity ultra-short laser pulses up to the femtosecond and even future attosecond range. The method employs a stacked diamond detector structure and the TOF technique, featuring high sensitivity, high resolution, high radiation hardness and high signal-to-noise ratio in environments heavily affected by remarkable EMP fields. A detailed study on the use, the optimization and the properties of a single module of the stack is here described for an experiment where a fast diamond detector is employed in an highly EMP-polluted environment. Accurate calibrated spectra of accelerated protons are presented from an experiment with the femtosecond Flame laser (beyond 100 TW power and ~ 10¹⁹ W/cm²intensity) interacting with thin foil targets. The results can be readily applied to the case of complex stack configurations and to more general experimental conditions.

We have recently proposed a new technique of plasma tailoring by laser-driven hydrodynamic shockwaves generated on both sides of a gas jet [Marquès et al., Phys. Plasmas 28, 023103 (2021)]. In a continuation of this numerical work, we study experimentally the influence of the tailoring on proton acceleration driven by a high-intensity picosecond laser in three cases: without tailoring, by tailoring only the entrance side of the picosecond laser, and by tailoring both sides of the gas jet. Without tailoring, the acceleration is transverse to the laser axis, with a low-energy exponential spectrum, produced by Coulomb explosion. When the front side of the gas jet is tailored, a forward acceleration appears, which is significantly enhanced when both the front and back sides of the plasma are tailored. This forward acceleration produces higher-energy protons, with a peaked spectrum, and is in good agreement with the mechanism of collisionless shock acceleration (CSA). The spatiotemporal evolution of the plasma profile is characterized by optical shadowgraphy of a probe beam. The refraction and absorption of this beam are simulated by post-processing 3D hydrodynamic simulations of the plasma tailoring. Comparison with the experimental results allows estimation of the thickness and near-critical density of the plasma slab produced by tailoring both sides of the gas jet. These parameters are in good agreement with those required for CSA.

Single crystal diamond detectors are widely employed in laser-induced plasma experiments to retrieve information about particles generated from the interaction. In particular, diamonds are used as Time of Flight (TOF) detectors featured by good sensitivity, high radiation hardness and fast response time. In this work, we provide a detailed characterization of two different types of electrodes configuration retrieving their charge collection efficiency, temporal response, and effective active area. The so obtained information are then used to compute calibrated proton spectra from the signals collected by the two investigated detectors employed in TOF schemes during an experimental campaign performed with the femtosecond FLAME laser (reaching >100 TW power and ~10¹⁹ W/cm² intensity) interacting with thin foil targets. Despite the different detection characteristics of the two diamond detectors, consistent information about the detected protons were obtained.

The time-of-flight technique coupled with semiconductor detectors is a powerful instrument to provide real-time characterization of ions accelerated because of laser–matter interactions. Nevertheless, the presence of strong electromagnetic pulses (EMPs) generated during the interactions can severely hinder its employment. For this reason, the diagnostic system must be designed to have high EMP shielding. Here we present a new advanced prototype of detector, developed at ENEA-Centro Ricerche Frascati (Italy), with a large-area (15 mm × 15 mm) polycrystalline diamond sensor having 150 μm thickness. The tailored detector design and testing ensure high sensitivity and, thanks to the fast temporal response, high-energy resolution of the reconstructed ion spectrum. The detector was offline calibrated and then successfully tested during an experimental campaign carried out at the PHELIX laser facility ( ${E}_L\sim$ 100 J, ${\tau}_L = 750$ fs, ${I}_L\sim \left(1{-}2.5\right)\times {10}^{19}$ W/cm²) at GSI (Germany). The high rejection to EMP fields was demonstrated and suitable calibrated spectra of the accelerated protons were obtained.

Particle-induced x-ray emission (PIXE) is a well-established ion-beam analysis technique, enabling quantitative measurement of the elemental composition of a sample surface under an ambient atmosphere with an external beam, which significantly simplifies the measurements, and is strictly necessary for those samples that cannot sustain a vacuum environment. Few-MeV electrostatic proton accelerators are used today in PIXE systems. We present here an external beam PIXE methodology based on a compact laser-driven proton accelerator. A 10-TW class ultrashort laser is used to generate a few-MeV proton beam, and a compact transport magnetic beamline is used to collect and transport the proton beam and to prevent unwanted fast electrons from reaching the sample. An x-ray CCD camera in single-photon detection mode is used to retrieve the spectrum of radiation emitted by the samples upon proton irradiation in air. Elemental composition analysis is performed and validated against standard energy-dispersive x-ray spectroscopy, demonstrating quantitative and accurate external beam PIXE analysis with compact laser-driven accelerators.

The aneutronic ¹¹B(p, α)2α fusion reaction driven by the interaction of high-energy lasers with matter has become a popular topic of research, since it represents a potential long-term goal alternative to the most studied deuterium-tritium reaction. However, the detection of the typical ionic products, especially alpha particles, of this low-rate fusion reaction is a challenging issue, due to their low flux. One of the diagnostic devices that can be implemented in laser-driven proton-boron fusion experiments is a Thomson spectrometer (TS), which is capable of detecting and discriminating ions according to their mass-to-charge ratio (A/Z, where A is the mass number and Z is the atomic number of the ions). In this work, we report on the ultimate test of a TS, which was designed and developed at the ENEA Research Centre in Frascati, Italy, in the context of a p + ¹¹B fusion experiment. Our device—designed to have high sensitivity and a robust shielding against electromagnetic pulses (EMPs)—was implemented at the PALS laser facility (∼700 J in ∼350 ps pulses) at a distance of 367 mm from the laser-plasma interaction point. We analyse here the measured signals obtained with our device, focusing on the assessment of their signal-to-background ratio. Despite the presence of strong EMPs and background radiation at such a short distance from the laser-irradiated target, the TS proved to be suitable for effectively detecting protons and heavier ions stemming from the plasma source.