Exploring phase contrast imaging with a laser-based Kα x-ray source up to relativistic laser intensity

Enriched traffic datasets for the city of Madrid: Integrating data from traffic sensors, the road infrastructure, calendar data and weather data

The proliferation of urban areas and the concurrent increase in vehicular mobility have escalated the urgency for advanced traffic management solutions. This data article introduces two traffic datasets from Madrid, collected between June 2022 and February 2024, to address the challenges of traffic management in urban areas. The first dataset provides detailed traffic flow measurements (vehicles per hour) from urban sensors and road networks, enriched with weather data, calendar data and road infrastructure details from OpenStreetMap. This combination allows for an in-depth analysis of urban mobility. Through preprocessing, data quality is ensured by eliminating inconsistent sensor readings. The second dataset is enhanced for advanced predictive modelling. It includes time-based transformations and a tailored preprocessing pipeline that standardizes numeric data, applies one-hot encoding to categorical features, and uses ordinal encoding for specific features. In constructing the datasets, we initially employed the k-means algorithm to cluster data from multiple sensors, thereby highlighting the most representative ones. This clustering can be adapted or modified according to the user's needs, ensuring flexibility for various analyses and applications. This work underscores the importance of advanced datasets in urban planning and highlights the versatility of these resources for multiple practical applications. We highlight the relevance of the collected data for a variety of essential purposes, including traffic prediction, infrastructure planning, studies on the environmental impact of traffic, event planning, and conducting simulations. These datasets not only provide a solid foundation for academic research but also for designing and implementing more effective and sustainable traffic policies. Furthermore, all related datasets, source code, and documentation have been made publicly available, encouraging further research and practical applications in traffic management and urban planning.

Vacuum-free femtosecond fiber laser microplasma X-ray source for radiography

Radiographic imaging using X-rays is a tool for basic research and applications in industry, materials science, and medical diagnostics. In this article, we present a novel approach for the generation of X-rays using a vacuum-free microplasma by femtosecond fiber laser. By tightly focusing a laser pulse onto a micrometer-sized solid density near-surface plasma from a rotating copper target, we demonstrate the generation of Cu K-photons (8-9 keV) with high yield ∼ 1.6 × 109 phot/s/2π, and with a source size diameter of approximately 10 microns. Femtosecond fiber laser allows working with a high repetition rate (∼2 MHz) and moderate energy levels (10-40 µJ), ensuring the effective quasi-continuous generation of X-ray photons. Furthermore, we introduce a hybrid scheme that combines the tightly focusing laser-plasma X-ray generator with an online control unit for microplasma size source based on the back-reflected second harmonic generated in the laser-induced microplasma. The compactness and high performance of this vacuum-free femtosecond fiber laser microplasma X-ray source makes it a promising solution for advanced radiographic applications. Our preliminary results on the creation of a microfocus X-ray source provide insights into the feasibility and potential of this innovative approach.

Experimental investigation of size broadening of a Kα x-ray source produced by high intensity laser pulses

The size of a hard Kα x-ray source ([Formula: see text] = 17.48 keV) produced by a high intensity femtosecond laser interacting with a solid molybdenum target is experimentally investigated for a wide range of laser intensity (I ~ 1017-2.8 × 1019 W/cm2) and for four values of the temporal contrast ratio (6.7 × 107 < CR < 3.3 × 1010). Results point out the size enlargement of the x-ray source with the increase of laser intensity and with the deterioration of temporal contrast. It amounts up to sixteen times the laser spot size at the highest laser intensity and for the lowest temporal contrast ratio. Using hydrodynamic simulations, we evaluate the density scale length of the pre-plasma L/λ just before the main pulse peak. This allows us to show that a direct correlation with the laser absorption mechanisms is not relevant to explain the large size broadening. By varying the thickness of the molybdenum target down to 4 µm, the impact of hot electron scattering inside the solid is also proved irrelevant to explain the evolution of both the x-ray source size and the Kα photon number. We deduce that the most probable mechanism yielding to the broadening of the source size is linked to the creation of surface electromagnetic fields which confine the hot electrons at the solid surface. This assumption is supported by dedicated experiments where the evolution of the size enlargement of the x-ray source is carefully studied as a function of the laser focal spot size for the highest contrast ratio.

Compact high-flux hard X-ray source driven by femtosecond mid-infrared pulses at a 1 kHz repetition rate

A novel, to the best of our knowledge, table-top hard X-ray source driven by femtosecond mid-infrared pulses provides 8 keV pulses at a 1 kHz repetition rate with an unprecedented flux of up to 1.5×10¹² X-ray photons/s. Sub-100 fs pulses at a center wavelength of 5 µm and multi-millijoule energy are generated in a four-stage optical parametric chirped-pulse amplifier and focused onto a thin Cu tape target. Electrons are extracted from the target and accelerated in a vacuum up to 100 keV kinetic energy during the optical cycle; the electrons generate a highly stable K α photon flux from the target in a transmission geometry.

Laser-driven x-ray and proton micro-source and application to simultaneous single-shot bi-modal radiographic imaging

Radiographic imaging with x-rays and protons is an omnipresent tool in basic research and applications in industry, material science and medical diagnostics. The information contained in both modalities can often be valuable in principle, but difficult to access simultaneously. Laser-driven solid-density plasma-sources deliver both kinds of radiation, but mostly single modalities have been explored for applications. Their potential for bi-modal radiographic imaging has never been fully realized, due to problems in generating appropriate sources and separating image modalities. Here, we report on the generation of proton and x-ray micro-sources in laser-plasma interactions of the focused Texas Petawatt laser with solid-density, micrometer-sized tungsten needles. We apply them for bi-modal radiographic imaging of biological and technological objects in a single laser shot. Thereby, advantages of laser-driven sources could be enriched beyond their small footprint by embracing their additional unique properties, including the spectral bandwidth, small source size and multi-mode emission.

Here the authors show a synchronized single-shot bi-modal x-ray and proton source based on laser-generated plasma. This source can be useful for radiographic and tomographic imaging.

Next-Generation Hardware Advances in CT: Cardiac Applications

Impending major hardware advances in cardiac CT include three areas: ultra-high-resolution (UHR) CT, photon-counting CT, and phase-contrast CT. Cardiac CT is a particularly demanding CT application that requires a high degree of temporal resolution, spatial resolution, and soft-tissue contrast in a moving structure. In this review, cardiac CT is used to highlight the strengths of these technical advances. UHR CT improves visualization of calcified and stented vessels but may result in increased noise and radiation exposure. Photon-counting CT uses multiple photon energies to reduce artifacts, improve contrast resolution, and perform material decomposition. Finally, phase-contrast CT uses x-ray refraction properties to improve spatial and soft-tissue contrast. This review describes these hardware advances in CT and their relevance to cardiovascular imaging.

Proof-of-concept Talbot-Lau x-ray interferometry with a high-intensity, high-repetition-rate, laser-driven K-alpha source

Talbot-Lau x-ray interferometry is a grating-based phase-contrast technique, which enables measurement of refractive index changes in matter with micrometric spatial resolution. The technique has been established using a variety of hard x-ray sources, including synchrotron, free-electron lasers, and x-ray tubes, and could be used in the optical range for low-density plasmas. The tremendous development of table-top high-power lasers makes the use of high-intensity, laser-driven K-alpha sources appealing for Talbot-Lau interferometer applications in both high-energy-density plasma experiments and biological imaging. To this end, we present the first, to the best of our knowledge, feasibility study of Talbot-Lau phase-contrast imaging using a high-repetition-rate laser of moderate energy (100 mJ at a repetition rate of 10 Hz) to irradiate a copper backlighter foil. The results from up to 900 laser pulses were integrated to form interferometric images. A constant fringe contrast of 20% is demonstrated over 100 accumulations, while the signal-to-noise ratio continued to increase with the number of shots. Phase retrieval is demonstrated without prior ex-situ phase stepping. Instead, correlation matrices are used to compensate for the displacement between reference acquisition and the probing of a PMMA target rod. The steps for improved measurements with more energetic laser systems are discussed. The final results are in good agreement with the theoretically predicted outcomes, demonstrating the applicability of this diagnostic to a range of laser facilities for use across several disciplines.