Sushil Singh

Real-time online diagnostics are essential for high-repetition-rate laser–plasma experiments, offering clear advantages over traditional, manually exchanged offline detectors, such as imaging plates, by eliminating the shot-to-shot processing time. Scintillator based detectors are widely used to measure bremsstrahlung radiation from laser–matter interactions, enabling the characterization of hot-electron distributions. In this study, we present absolute calibration of a lutetium–yttrium oxyorthosilicate crystal-based multilayer scintillator stack spectrometer performed at the MT25 microtron facility in Prague. Bremsstrahlung radiation was generated by irradiating a tungsten converter with monoenergetic electron beams in the energy range between 5 MeV and 22 MeV. The response of the individual crystal was measured and compared with the energy deposition calculated using the Fluktuierende Kaskade (FLUKA) Monte Carlo simulation. A linear correlation between signal response and energy deposition was obtained for all crystals within the experimental uncertainty, confirming detector linearity with the calibration factor 0.014 ± 0.002 ADU/keV (where ADU denotes the analog-to-digital unit). This calibration enables quantitative, real-time measurement of bremsstrahlung spectra and is valuable for particle acceleration, high-intensity laser–plasma experiments, laboratory astrophysics, warm dense matter, and inertial confinement fusion studies.

In this contribution, we present the results of a long-term study on radiofrequency and microwave electromagnetic pulse (EMP) emission, a phenomenon that is still not satisfactorily explained, performed at the PALS iodine laser system (1315 nm, 0.3 ns, up to 700 J on target). Using a comprehensive set of broadband diagnostics, including double ridged horn antennas, target current probe, along with special low-loss cables and oscilloscopes with sampling rates up to 100 GS/s, we observed an unprecedentedly broad EMP spectrum with frequencies significantly exceeding 10 GHz. Moreover, scaling experiments revealed a dependence of the spectral shape and its central frequency on the laser intensity, and this was further correlated with electron emission. This dependence indicates that in addition to the well-known influence of the eigenfrequencies of the experimental hardware (e.g., target, stalk, and chamber), processes associated with the expanding plasma can also play a dominant role, as demonstrated in this study. We believe that these new findings will not only contribute to EMP mitigation and deepen our understanding of fundamental physics, but also support high-tech applications such as EMP hardening, biomedical research, and defense technologies.

Recent advances in ion diagnostics for laser-induced plasma experiments have improved system design and data analysis. Measuring charged particle emissions from laser-irradiated targets provides valuable insights into laser–matter interactions. Among real-time diagnostics, Time-of-Flight (TOF) detectors are reliable systems for analyzing particle beam properties such as kinetic energy and shot-to-shot reproducibility. Diamond-based detectors are ideal for TOF measurements due to their fast response time, radiation hardness, and low leakage current. However, TOF detectors lack particle discrimination. To overcome this, a Multi Filter Diamond Array (MFDA) was developed using six nominally identical single crystal diamond detectors paired with aluminum foils of different thicknesses to exploit particle stopping power differences. The MFDA was tested at the Prague Asterix Laser System during an experimental campaign in the framework of the FUSION project, and data analysis was performed. A cross-validation with other diagnostics, including a Thomson Parabola Spectrometer and CR-39 detectors, is also presented.

The hybrid model combines deep neural networks (DNN) and large AI models, such as large language models (LLM), for enhanced clinical information retrieval (CIR) from electronic clinical records (ECR). While LLMs show promise for encoding complex medical data, they face challenges in user-dependent information, such as patient reports with encoded knowledge, accessing real-time data, and requiring extensive fine-tuning for clinical decision-making in online communication systems. To overcome these limitations, we introduce a Transformer-based Sequence (TBS) multimodal method that integrates representation learning with human expertise to encode and analyze intricate relationships within clinical data. This model improves predictive tasks and medical search accuracy, achieving F1-scores of 0.83-0.80, and outperforms baseline methods. Integrating AI-driven methodologies in healthcare has the potential to transform medical record analysis and utilization, resulting in enhanced patient outcomes and more personalized healthcare solutions.

In this work, we discuss the challenges related to the preliminary investigation of high repetition rate (HRR) experiments in the field of high energy density (HED) physics, and we present the results of preparation experiments done at the Prague Asterix Laser System (PALS) laser facility conducted with the aim of defining the needed developments in target design, real-time diagnostics and data collection needed to meet HRR requirements. Although the PALS laser facility is not an HRR facility, it has served as a valuable test bed for advancing diagnostic techniques and refining target design in preparation for HRR experimental platforms. HRR operation will result in improved statistical errors of the experimental results, in particular for experiments related to equation of state studies in extreme conditions.

Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering (SSRS) instability could reduce laser–plasma coupling and generate considerable fluxes of suprathermal hot electrons under interaction conditions envisaged for direct-drive schemes for inertial confinement fusion. Nonetheless, SSRS remains to date one of the least understood parametric instabilities. Here, we report the first angularly and spectrally resolved measurements of scattered light at laser intensities relevant for the shock ignition scheme (I ∼ 1016 W/cm2), showing significant SSRS growth in the direction perpendicular to the laser polarization. Modification of the focal spot shape and orientation, obtained by using two different random phase plates, and of the density gradient of the plasma, by utilizing exploding foil targets of different thicknesses, clearly reveals a different dependence of backward SRS (BSRS) and SSRS on experimental parameters. While convective BSRS scales with plasma density scale length, as expected by linear theory, the growth of SSRS depends on the spot extension in the direction perpendicular to laser polarization. Our analysis therefore demonstrates that under current experimental conditions, with density scale lengths Ln ≈ 60–120 μm and spot sizes FWHM ≈ 40–100 μm, SSRS is limited by laser beam size rather than by the density scale length of the plasma.

We experimentally demonstrate the generation of quasi-monoenergetic electron bunch at the end of the electron energy distribution. The experiment was conducted at the Prague Asterix Laser System where iodine laser supplies laser energy up to 600 J at the fundamental wavelength of 1.315 μm with a pulse duration of 350 ps. The thickness of different target materials (Cu, Sn, Ta, Pb) was varied between 10 and 25 μm. The energy spectrum of electrons was measured using an array of electron spectrometers at different angular directions with respect to the laser axis. Three frame femtosecond interferometry driven by a Ti:Sa laser was implemented to scan the changes in electron density during plasma ignition by the iodine laser. The experimental results indicate the generation of well-defined quasi-monoenergetic peaks in the electron energy distribution. The energy range of the measured quasi-monoenergetic peaks lies between 0.6 and 1.5 MeV; however, the energy spread of the distribution varies between 4% and 12%. These features were observed consistently in the electron spectrum and illustrate the quasi-monoenergetic electron beam generation by interaction of a sub-nanosecond laser beam with plasma. In addition, a comparison of electron spectra from spectrometers located in opposite directions relative to the position of the laser focus indicates the splitting of the electron cloud into plasma blocks during the acceleration of hot electrons by Coulomb repulsion. These findings can be applicable in fast electron beam-driven radiation sources, electromagnetic pulse generation, charge particle acceleration, and inertial fusion studies.

Driving of the nuclear fusion reaction p + 11B → 3α + 8.7 MeV under laboratory conditions by interaction between high-power laser pulses and matter has become a popular field of research, owing to its numerous potential applications: as an alternative to deuterium–tritium for fusion energy production, astrophysics studies, and alpha-particle generation for medical treatment. One possible scheme for laser-driven p–11B reactions is to direct a beam of laser-accelerated protons onto a boron (B) sample (the so-called “pitcher-catcher” scheme). This technique has been successfully implemented on large high-energy lasers, yielding hundreds of joules per shot at low repetition. We present here a complementary approach, exploiting the high repetition rate of the VEGA III petawatt laser at CLPU (Spain), aiming at accumulating results from many interactions at much lower energy, to provide better control of the parameters and the statistics of the measurements. Despite a moderate energy per pulse, our experiment allowed exploration of the laser-driven fusion process with tens (up to hundreds) of laser shots. The experiment provided a clear signature of the reactions involved and of the fusion products, accumulated over many shots, leading to an improved optimization of the diagnostics for experimental campaigns of this type. In this paper, we discuss the effectiveness of laser-driven p–11B fusion in the pitcher–catcher scheme, at a high repetition rate, addressing the challenges of this experimental scheme and highlighting its critical aspects. Our proposed methodology allows evaluation of the performance of this scheme for laser-driven alpha particle production and can be adapted to high-repetition-rate laser facilities with higher energy and intensity.