Amplitude Technologies (France)

In this work, investigations of the interaction between borosilicate glass and three laser regimes are presented: repetitive single pulse, MHz-burst, and GHz-burst. Experiments were carried out using an ultrafast industrial laser system and galvanometric scanning to inscribe bulk modifications inside borosilicate glass (N-BK7) samples. By varying pulse or burst energy and scanning velocity, we produced a wide range of in-volume modification morphologies. This approach enabled to classify modifications and establish processing maps for each regime. Results show that the single-pulse regime is more suited for generating large, defect-free bulk modifications with a teardrop shape, while the MHz-burst regime increases the probability of defect formation, including voids and local cracking. These defects become even more pronounced under GHz-burst irradiation, where the lower energy per pulse results in absorption mainly near the focal point, leading to crack formation. Overall, this work provides a comprehensive understanding of glass behavior under femtosecond laser irradiation and provides guidelines for selecting laser conditions suitable for transparent glass welding.

Laser-plasma accelerators emerge as ultra-compact and versatile sources for numerous applications. Although the acceleration length is short (a few millimeters), they typically require large-scale infrastructures including ultra-high-power lasers, vacuum chambers and strict stability for temperature and humidity. As a result, most experiments are conducted in laboratories in large areas with controlled environments. Here, we present a highly compact (footprint of ~ 9 m²) and transportable system capable of generating electrons and photons in the MeV range at high repetition rates (up to 10 Hz) with average charge levels of 0.5 nC and up to 1 nC. This achievement shows the feasibility of performing laser-plasma acceleration outside of laboratory environments with a transportable system, significantly expanding the potential for practical applications.

Development trends of high intensity laser systems points in the direction of increasing the repetition rate towards 10 Hz and beyond, while reliability and stability is also greatly improved [1], [2]. Next generation of particle and high harmonic beamlines require stable temporal compression of the driver pulses together with high spatio-temporal quality. Operation of the HFPW laser of the ALPS Facility of ELI ERIC has been recently demonstrated at the 700 TW level at 10 Hz repetition rate [3]. Intensity contrast and spectral stability requirements of experiments push the boundaries of currently available laser frontends. Furthermore, the high repetition rate and consequently the high average power also put a high demand on the final amplifiers, and on the vacuum compressor optical elements.

Segmentation of individual thigh muscles in MRI images is essential for monitoring neuromuscular diseases and quantifying relevant biomarkers such as fat fraction (FF). Deep learning approaches such as U-Net have demonstrated effectiveness in this field. However, the impact of reducing neural network complexity remains unexplored in the FF quantification in individual muscles. U-Net architectures with different complexities have been compared for the quantification of the fat fraction in each muscle group selected in the central part of the thigh region. The corresponding performance has been assessed in terms of Dice score (DSC) and FF quantification error. The database contained 1450 thigh images from 59 patients and 14 healthy subjects (age: 47 ± 17years, sex: 36F, 37M). Ten individual muscles were segmented in each image. The performance of each model was compared to nnU-Net, a complex architecture with 4.35 107 parameters, 12.8 Gigabytes of peak memory usage and 167h of training time. As expected, nnU-Net achieved the highest DSC (94.77 ± 0.13%). A simpler U-Net (5.81 105 parameters, 2.37 Gigabytes, 14h of training time) achieved a lower DSC but still above 90%. Surprisingly, both models achieved a comparable FF estimation. The poor correlation between observed DSC and FF indicates that less complex architectures, reducing GPU memory utilization and training time, can still accurately quantify FF.

International audience

ABSTRACT This paper describes technical details and new scientific opportunities offered by the new High Power Laser Facility at the ESRF, opened to users since 2022. This facility enables laser-induced dynamic compression experiments probed by ultra-fast X-ray Absorption Spectroscopy at beamline ID24-ED. This capability allows to reach and probe more extreme pressure and temperature states and higher strain rates with respect to static compression, addressing open questions in fundamental, planetary and material science.