Beam Size Research Articles

Commissioning of a gantry beamline with rotator at a synchrotron-based ion therapy center

This paper provides an overview of the worldwide first commissioning of a gantry beamline with a rotator at the MedAustron synchrotron-based proton/ion cancer therapy facility in Wiener Neustadt, Austria. The gantry beamline consists of the high energy beam transfer (HEBT) line and the gantry beam transport system. It transports the beam from the synchrotron to the gantry-room isocenter. The HEBT transports the beam from the synchrotron to the gantry entrance, which is the coupling point between the HEBT and the gantry. The rotator is one of the HEBT modules, thus it is an integral part of the gantry beamline. The MedAustron rotator is the worldwide first rotator system used to match slowly extracted asymmetric beams from the synchrotron to the rotating gantry. In this paper, main attention is paid to ion-optical and beam-alignment aspects of the beamline commissioning. A novel orbit-correction and beam-alignment technique has been developed specifically for the beamline with the rotator. While the theoretical concept of the rotator has existed for almost two decades, the MedAustron rotator is the first hardware implementation of this concept all over the world. The presented overview of the beamline commissioning includes a description of the principal technical solutions and main results of the first beam-transport measurements. Since the measured beam size and beam position agree well with theoretical predictions, one can conclude that the proof-of-concept of the rotator-matching has been successfully accomplished. Published by the American Physical Society 2024

Single high-energy arc proton therapy with Bragg peak boost (SHARP).

Because of the co-location of critical organs at risk, base of skull tumours require steep dose gradients to achieve the prescribed dosimetric criteria. When available, proton beam therapy (PBT) is often considered a desirable modality for these cases, but in many instances, compromises in target coverage are still required to achieve critical organ at risk (OAR) tolerance doses. A number of techniques have been proposed to further improve the penumbra of PBT. In the current study, we propose a novel, collimator-free treatment planning technique that combines high-energy shoot-through proton beams with conventional Bragg peak spot placement. The small spot size of the high-energy pencil beams provides a sharp penumbra at the target boundary, and the Bragg peak spots provide a higher linear energy transfer (LET) boost to the target centre. Three base of skull chordoma patients were retrospectively planned with three different PBT treatment planning techniques: (1) conventional intensity-modulated proton therapy (IMPT); (2) high-energy proton arc therapy (HE-PAT); and (3) the novel technique combining HE-PAT and IMPT, referred to as single high-energy arc with Bragg peak boost (SHARP). The Monaco 6 treatment planning system was used. SHARP was found to improve the PBT penumbra in the plane perpendicular to the HE-PAT beams. Minimal penumbra differences were observed in the plane of the HE-PAT beams. SHARP reduced dose-averaged LET to surrounding organs at risk. A novel PBT treatment planning technique was successfully implemented. Initial results indicate the potential for SHARP to improve the penumbra of PBT treatments for base of skull tumours.

Sub-micrometre focusing of intense 100 keV X-rays with multilayer reflective optics.

A high-flux sub-micrometre focusing system was constructed using multilayer focusing mirrors in Kirkpatrick-Baez geometry for 100 keV X-rays. The focusing mirror system had a wide bandwidth of 5% and a high peak reflectivity of 74%. Performance was evaluated at the undulator beamline BL05XU of SPring-8, which produced an intense 100 keV X-ray beam with a bandwidth of 1%. When the light source was focused directly in both vertical and horizontal directions, the beam size was measured to be 0.32 µm (V) × 5.3 µm (H) with a flux of 1 × 1012 photons s-1. However, when a limited horizontal slit was used to form a secondary source, the focusing beam size decreased to 0.25 µm (V) × 0.26 µm (H) with a flux of 6 × 1010 photons s-1. The 200 nm line and space patterns of a Siemens star chart made of tantalum were clearly resolved by the absorption contrast of the focused beam. This 100 keV focusing system is applicable to various fields of nondestructive analyses with sub-micrometre resolutions.

Optimization of synchrotron radiation parameters using swarm intelligence and evolutionary algorithms.

Alignment of each optical element at a synchrotron beamline takes days, even weeks, for each experiment costing valuable beam time. Evolutionary algorithms (EAs), efficient heuristic search methods based on Darwinian evolution, can be utilized for multi-objective optimization problems in different application areas. In this study, the flux and spot size of a synchrotron beam are optimized for two different experimental setups including optical elements such as lenses and mirrors. Calculations were carried out with the X-ray Tracer beamline simulator using swarm intelligence (SI) algorithms and for comparison the same setups were optimized with EAs. The EAs and SI algorithms used in this study for two different experimental setups are the Genetic Algorithm (GA), Non-dominated Sorting Genetic Algorithm II (NSGA-II), Particle Swarm Optimization (PSO) and Artificial Bee Colony (ABC). While one of the algorithms optimizes the lens position, the other focuses on optimizing the focal distances of Kirkpatrick-Baez mirrors. First, mono-objective evolutionary algorithms were used and the spot size or flux values checked separately. After comparison of mono-objective algorithms, the multi-objective evolutionary algorithm NSGA-II was run for both objectives - minimum spot size and maximum flux. Every algorithm configuration was run several times for Monte Carlo simulations since these processes generate random solutions and the simulator also produces solutions that are stochastic. The results show that the PSO algorithm gives the best values over all setups.

Effect of size factor and tapered angles on the shear behavior and strength of haunched beams reinforced with basalt fiber reinforced polymer rebars: Experimental and analytical study

Haunched beams are beams that exhibit varying effective depth over their span. This study includes an experimental and analytical analysis aimed at investigating the influence of size factor on the shear behavior of tapered beams reinforced with basalt fiber reinforced polymer BFRP bars. The main focus of this study revolves around investigating the effects of both inclination angle and size factor as key variables. In this study, a total of eight simply supported beams were tested. The beams were longitudinally reinforced with a 1% ratio of BFRP reinforcement, and separated into two equal groups. Each group consisted of one straight beam and three haunched beams. The haunched beams had varied tapering angles, namely 4⁰, 7.96⁰, and 11.86⁰. The first group is designated for the allocation of large beams, while the second group is designated for the allocation of small beams, which have a cross-section that is one-fourth the size of the large beams. The test results indicate that an increase in tapered angles leads to an increase in shear strength. Additionally, it was observed that smaller beams exhibited a greater normalized shear strength compared to larger beams with a significant rate as compared with straight beams. Subsequently, two equations were developed using the tested data, whereby one of them represents an optimal equation including a logical safety margin, while the other equation is characterized by a conservative equation, providing a substantial safety margin for predictions.

Synthesis of Nickel-Based Nanoparticles by Pulsed Laser Ablation in Liquids: Correlations between Laser Beam Power, Size Distribution and Cavitation Bubble Lifetime

Pulsed laser ablation in liquids (PLAL) is a colloidal synthesis technique attracting significant interest from the scientific community due to the quality of the nanoparticles being produced. In this type of synthesis protocol, the cavitation bubble plays a vital role during the synthesis of nanoparticles. This work studied the effect of the laser beam power on cavitation bubble lifetime. Three different laser beam power values (5.8 W, 7.5 W and 10.5 W) were used to irradiate a pure nickel target in de-ionized (DI) water to synthesize nickel-based nanoparticles. The optimal repetition rate maximizing the production of nanoparticles was determined by atomic emission spectroscopy for each laser beam power. It was determined that the optimal repetition rate increased exponentially with laser beam power, while the cavitation bubble lifetime decreased logarithmically with the laser beam power. Moreover, the effect of the laser beam power on the cavitation bubble lifetime also had an effect on the size distribution of the nanoparticles being produced; the smallest size distribution was obtained at the highest laser beam power.

Ammonia observations of Planck cold cores

Single-pointing observations of NH$_ $\,(1,1) and (2,2) were conducted toward 672 Planck Early Cold Cores (ECCs) using the Nanshan 26-m radio telescope. Out of these sources, a detection rate of 37<!PCT!> (249 cores) was achieved, with a $\,(1,1) hyperfine structure detected in 187 cores and $\,(2,2) emission lines detected in 76 of them. The detection rate of $ is positively correlated with the continuum emission fluxes at a frequency of 857\,GHz. Among the observed 672 cores, sim 22<!PCT!> have associated stellar and infrared objects within the beam size (sim 2arcmin ). This suggests that most of the cores in our sample may be starless. The kinetic temperatures of the cores range from 8.9 to 20.7\,K, with an average of 12.3\,K, indicating a coupling between gas and dust temperatures. The ammonia column densities range from 3.6\,times \,1014 to 6.07\,times $, with a median value of 2.04\,times $. The fractional abundances of ammonia range from 0.3 to 9.7\,times $, with an average of 2.7\,times $, which is one order of magnitude larger than that of massive star-forming (MSF) regions and infrared dark clouds (IRDCs). The correlation between thermal and nonthermal velocity dispersion of the NH$_ $\,(1,1) inversion transition indicates the dominance of supersonic nonthermal motions in the dense gas traced by $, and the relationship between these two parameters in Planck cold cores is weaker, with lower values observed for both parameters relative to other samples under our examination. The cumulative distribution shapes of line widths in the Planck cold cores closely resemble those of the dense cores found in regions of Cepheus, in addition to Orion L1630 and L1641, with higher values compared to Ophiuchus.

Integrated Deep Ultraviolet Doublet Metalens for Projection Imaging

Metalenses, with their unique modulation of light, are in great demand for many potential applications. As a proof-of-principle demonstration, we focus on designing SiO2 metalenses that operate in the deep ultraviolet region, specifically around 193 nm. Based on the deep ultraviolet metalens proposed in this paper, an integrated deep ultraviolet doublet metalens is further offered. When the incident light is a plane wave with a wavelength of 193 nm, the integrated doublet metalens can reduce the beam size by a factor of 4:1, and the emitted light is flat. The integrated doublet metalens can project the reticle image proportionally, making the projection image clear. The integrated doublet metalens has the best imaging effect at the propagation distance of 2 μm and can tolerate ±3 degrees of incident angle deviation. Our findings establish general and systematic strategies to guide the design of traditional optical lens arrays with excellent integrated doublet metalenses and pave the way for enhanced optical performance in the application of large-relative-aperture deep ultraviolet detection, deep ultraviolet microscope systems, laser beam combining systems, deep ultraviolet lithography systems, etc.

Comparative Study of the Behavior and Strength of Laterally Supported Steel Beams with Laterally Unsupported Steel Beams

A laterally supported beam is a beam that is supported along its length to prevent lateral buckling. Lateral support can be provided by bracing, sheathing, or other means to prevent the beam form deflecting laterally. This type of support is important in preventing the beam from failing under the influence of lateral loads, such as wind or seismic forces. In contrast, a laterally unrestrained beam is a beam that is not restraint(transversely) along its length which its top flange will be subjected to lateral torsional buckling. To prevent this type of buckling, both flanges of the section or at least its top flange must have lateral support. In a beam, if the flange or its compression region is sufficiently prevented from displacement and twisting, or when the compression flange is directly connected to the roof, the beam is considered braced at the same point. This paper aims to investigate the comparison of behavior and strength between fully laterally supported and laterally unsupported beams in steel structures. To carry out this study, extensive parametric analysis is performed by considering different sizes of beams, spacing of the lateral supports and comparing the strength of laterally supported beam compared with laterally unsupported beam by practical examples. The findings shows that if the steel beams have full lateral support, the plastic hinge is created at the point with the maximum moment and the strength of that beams is not limited by lateral torsional buckling. on the contrary, if the same steel beam does not have lateral support or the unbraced length of compression flange are very large, its strength is limited by lateral torsional buckling, and its strength is more than 15 % lower than if it has a continues lateral support.

Temporal and Spatial Beam Shaping in LPBF for Fine and Porous Ti-Alloy Structures for Regenerative Fuel Cell Applications

AbstractLaser Powder Bed Fusion (LPBF) presents itself as a potential method to produce thin porous structures, which have numerous applications in the medical and energy industries, due to its in-process pore formation capabilities. Particularly, regenerative fuel cells, which are capable of both producing and storing energy through the use of hydrogen-based electrochemical fuel cell and electrolysers, respectively, can benefit from the LPBF-induced porosity for it porous layer components in the electrode. Numerous studies have reported that process parameters, such as laser power, scan speed and hatch spacing, are key factors affecting the formation of pores in LPBF material due to their control over the energy density and melt pool formation during the build. Contemporary fibre lasers offer novel temporal and spatial beam shaping capabilities. Temporal laser control means that the laser can use pulsed wave (PW) or single point exposure (SPE), and spatial beam shaping refers to variations in the intensity distribution of the laser, which can be modulated from Gaussian to ring shape via the use of multi-core fibers. These have seldom been studied in combination with LPBF. Therefore, the aim of this study was to utilise temporal and spatial beam shaping in LPBF to produce thin porous structures. To do this, PW and SPE laser temporal strategies were utilised and the duty cycle (which relates the on and off time of the laser) was varied between 50% and 100%. Beam shape indexes 0 (Gaussian), 3 and 6 (ring) were also investigated alongside more standard LPBF process parameters such as laser power and scan speed to manufacture thin porous walls, as well as fine struts. The thinnest wall obtained was 130 μm thick, while the smallest strut had a diameter of 168 μm. The duty cycle had a clear effect on the porosity of thin walls, where a duty cycle of 50% produced the highest number of porous walls and had the highest porosity due to its ability to control the intensity of the energy density during the LPBF process. The different beam shape indexes corresponded to different spatial distribution of the power density, and hence, modifying the temperature distribution in the meltpool during the laser material interaction. Beam shape index 6 (corresponding to a ring mode with lower peak irradiance) created more porous specimens and smaller meltpool sizes, with respect to its beam size. Overall, this study showed that temporal and spatial control of the beam (through duty cycle and beam shape index) are powerful tools which can control the distribution and intensity of the energy density during the LPBF process to produce thin porous structures for energy applications.

Automatic 4-mirrors system for alignment of high-power laser radiation

This paper presents the automated system for minimizing the deviation of the path of passage and the divergence of a secondary radiation source with parameters similar to ones of the main beam of a high-power Ti:Sa laser using mirrors in kinematic mounts on the motorized stages. As an alignment laser, the diode laser with a fiber output was used with radiation characteristics coinciding with the parameters of the main beam (wavelength, beam diameter). The successive approximation algorithm was used to minimize the beam deflection. The positioning accuracy and beam size matching were analyzed on the near-field camera and were equaled to 28.6 µm along the X-axis and 26.4 µm along the Y-axis. Beam size mismatch was equaled to 0.151 mm. The pointing accuracy was analyzed on the far-field sensor and equaled 15.34 µrad along the X axis and 12.03 µrad along the Y axis. The curvature of the wavefront was 0.06 µm.

High-resolution ALMA observations of compact discs in the wide-binary system Sz 65 and Sz 66

Context. Substructures in disc density are ubiquitous in the bright extended discs that are observed with high resolution. These substructures are intimately linked to the physical mechanisms driving planet formation and disc evolution. Surveys of star-forming regions find that most discs are in fact compact, less luminous, and do not exhibit these same substructures. It remains unclear whether compact discs also have similar substructures or if they are featureless. This suggests that different planet formation and disc evolution mechanisms operate in these discs. Aims. We investigated evidence of substructure within two compact discs around the stars Sz 65 and Sz 66 using high angular resolution observations with ALMA at 1.3 mm. The two stars form a wide-binary system with 6″.36 separation. The continuum observations achieve a synthesised beam size of 0″.026 × 0″.018, equivalent to about 4.0 × 2.8 au, enabling a search for substructure on these spatial scales and a characterisation of the gas and dust disc sizes with high precision. Methods. We analysed the data in the image plane through an analysis of reconstructed images, as well as in the uv plane by non-parametrically modelling the visibilities and by an analysis of the 12CO (2–1) emission line. Comparisons were made with highresolution observations of compact discs and radially extended discs. Results. We find evidence of substructure in the dust distribution of Sz 65, namely a shallow gap centred at ≈20 au, with an emission ring exterior to it at the outer edge of the disc. Ninety percent of the measured continuum flux is found within 27 au, and the distance for 12CO is 161 au. The observations show that Sz 66 is very compact: 90% of the flux is contained within 16 au, and 90% of the molecular gas flux lies within 64 au. Conclusions. While the overall prevalence and diversity of substructure in compact discs relative to larger discs is yet to be determined, we find evidence that substructures can exist in compact discs.

Uptake and accumulation mechanisms of hexachloroplatinate(IV) ions in the unicellular alga, Pseudococcomyxa simplex.

Platinum uptake was examined by adding hexachloroplatinate(IV) solution to the unicellular alga Pseudococcomyxa simplex. After the addition of platinum solution ([Pt] = 100mg/kg, pH 3.2-3.2) for a certain time, the cells were quickly frozen and subjected to μ-XRF (X-ray fluorescence) analysis using synchrotron X-rays. The beam size of approximately 1 micrometer allowed visualization of the platinum distribution within a single cell. On the other hand, we examined platinum uptake in enzyme-treated protoplasts and lyophilized cells and found that the platinum uptake concentrations in these samples were higher than in living in-vivo cells. Cell wall and cell metabolism were presumed to interfere with the uptake of hexachloroplatinate(IV) ions. All platinum ions taken up by the cells were reduced to divalent form. The effect of light on platinum addition was also investigated. When platinum was added under light conditions, some samples showed higher platinum accumulation than under shade conditions.

Ionic-resolution protoacoustic microscopy: A feasibility study.

Visualizing micro- and nano-scale biological entities requires high-resolution imaging and is conventionally achieved via optical microscopic techniques. Optical diffraction limits their resolution to ∼200 nm. This limit can be overcome by using ions with ∼1 MeV energy. Such ions penetrate through several micrometers in tissues, and their much shorter de Broglie wavelengths indicate that these ion beams can be focused to much shorter scales and hence can potentially facilitate higher resolution as compared to the optical techniques. Proton microscopy with ∼1 MeV protons has been shown to have reasonable inherent contrast between sub-cellular organelles. However, being a transmission-based modality, it is unsuitable for in vivo studies and cannot facilitate three-dimensional imaging from a single raster scan. Here, we propose proton-induced acoustic microscopy (PrAM), a technique based on pulsed proton irradiation and proton-induced acoustic signal collection. This technique is capable of label-free, super-resolution, 3D imaging with a single raster scan. Converting radiation energy into ultrasound enables PrAM with reflection mode detection, making it suitable for in vivo imaging and probing deeper than proton scanning transmission ion microscopy (STIM). Using a proton STIM image of HeLa cells, a coupled Monte Carlo+k-wave simulations-based feasibility study has been performed to demonstrate the capabilities of PrAM. We demonstrate that sub-50 nm lateral (depending upon the beam size and energy) and sub-micron axial resolution (based on acoustic detection bandwidth and proton beam pulse width) can be obtained using the proposed modality. By enabling visualization of biological phenomena at cellular and subcellular levels, this high-resolution microscopic technique enhances understanding of intricate cellular processes.

A modern approach to diagnostic methods of the cornea and aqueous humor of anterior chamber of the eye in patients with anterior uveitis, associated with spondyloarthritis

Anterior uveitis is the dominant clinical extra-articular manifestation of spondyloarthritis associated with the carriage of the human leukocyte antigen allele (HLA-B27), which may precede joint and spinal involvement. In 20–30% of cases, uveitis occurs with frequent relapses – up to 5–6 exacerbations per year, often has a protracted character and is poorly amenable to local anti-inflammatory therapy, which leads to a decrease in vision and a deterioration in the quality of life. Timely and accurate assessment of the severity of intraocular inflammation plays an important role in making a diagnosis and in choosing the right treatment tactics for treating anterior uveitis in patients with HLA-B27-associated spondyloarthritis. The current standard clinical approach to assessing inflammation is the presence and number of inflammatory cells in the anterior chamber aqua humor according to the SUN classification using slit lamp imaging. However, the assessment of SUN is very subjective. Moreover, the individual variability in anterior chamber cell count, which is the main diagnostic criterion for uveitis, can be exacerbated by certain testing conditions, such as the brightness of the slit lamp light bar, light beam size calibration, light source intensity. Advances in optical imaging technology, the application of the latest technologies and the improvement of already known methods offer new opportunities for an objective, accurate and quantitative assessment of inflammation. The article describes the possibilities of studying the cornea and the anterior chamber of the eye using anterior segment optical coherence tomography, confocal microscopy of the cornea and keratotopometry.

Timber-concrete composites (TCC) floors subjected to hogging moment

In this paper, the structural behaviour of timber precast concrete composite (TCC) beam-to-column subassemblies subjected to hogging bending moments is investigated. Full-scale testing and analytical modelling are undertaken on timber precast concrete composite joints and beams. The composite actions were transferred via coach (lag) screw shear connectors embedded in the small grout pockets. The laboratory tests were designed to determine the influence of the size and type of timber beams (i.e., laminated veneer lumber (LVL) or glued laminated timber (GLT)), size of screw shear connectors and amount of reinforcement (in the slabs) on the structural behaviour (i.e., load-displacement, stiffness, capacity, and ductility) of the TCC beam-to-column connections. The hogging moment capacity and stiffness of the TCC floors with nominal slab thickness of 80 mm and reinforcing ratio (in the range of 0.9–1.8%) were up to 24% and 17% higher than that of the bare timber beam, respectively. The size of coach screw shear connectors (in the range of 8–16 mm) had less than 13% effect on the capacity and stiffness. An analytical model for calculating the peak load and stiffness of the TCC beams under hogging bending moment is developed. The model is shown to perform well when compared to the collected test data.

Broadband sub-wavelength terahertz subsurface imaging using a solid-immersion lens

We demonstrate a broadband sub-wavelength terahertz (THz) imaging system by combining a solid-immersion lens (SIL) with a THz time-domain spectrometer (TDS). The imaging resolution of the system is enhanced in a wide spectral range (from 0.3 to 2.0 THz) with the aid of the SIL. The beam size is within 120–280 μm (0.28–0.8 λ) in the measured frequency range. Experimentally achieved imaging resolution enhancement results are consistent with the numerical simulation results. Unlike the previous reports on imaging systems using SIL, the beam size reduction by the SIL is more than a factor of nSIL (3.42) for all frequencies near the focal spot. An analytical calculation is employed to obtain insights into the beam size reduction mechanism and estimate the beam size in a given experimental condition. THz image of the WR1.9 waveguide is measured to highlight the broadband sub-wavelength imaging capability. The increased reflection from the waveguide near the cutoff frequency for TE10 and TE01 modes, inaccessible with other THz-TDS-based or continuous wave (CW) source-based THz imaging systems, is experimentally observed. In addition, we show the multispectral sub-wavelength images of subsurface structures by selecting the appropriate measurement time window of the temporal THz signal. THz images of a credit card show the sub-wavelength details of the card, including an IC chip, invisible due to the plastic cover. The experimental results highlight the potential applications of the imaging system in non-contact, non-destructive testing of the sub-wavelength scale structures in various fields.

Enhanced RBE of Particle Radiation Depends on Beam Size in the Micrometer Range.

High-linear energy transfer (LET) radiation, such as heavy ions is associated with a higher relative biological effectiveness (RBE) than low-LET radiation, such as photons. Irradiation with low- and high-LET particles differ in the interaction with the cellular matter and therefore in the spatial dose distribution. When a single high-LET particle interacts with matter, it results in doses of up to thousands of gray (Gy) locally concentrated around the ion trajectory, whereas the mean dose averaged over the target, such as a cell nucleus is only in the range of a Gy. DNA damage therefore accumulates in this small volume. In contrast, up to hundreds of low-LET particle hits are required to achieve the same mean dose, resulting in a quasi-homogeneous damage distribution throughout the cell nucleus. In this study, we investigated the dependence of RBE from different spatial dose depositions using different focused beam spot sizes of proton radiation with respect to the induction of chromosome aberrations and clonogenic cell survival. Human-hamster hybrid (AL) as well as Chinese hamster ovary cells (CHO-K1) were irradiated with focused low LET protons of 20 MeV (LET = 2.6 keV/µm) beam energy with a mean dose of 1.7 Gy in a quadratic matrix pattern with point spacing of 5.4 × 5.4 µm2 and 117 protons per matrix point at the ion microbeam SNAKE using different beam spot sizes between 0.8 µm and 2.8 µm (full width at half maximum). The dose-response curves of X-ray reference radiation were used to determine the RBE after a 1.7 Gy dose of radiation. The RBE for the induction of dicentric chromosomes and cell inactivation was increased after irradiation with the smallest beam spot diameter (0.8 µm for chromosome aberration experiments and 1.0 µm for cell survival experiments) compared to homogeneous proton radiation but was still below the RBE of a corresponding high LET single ion hit. By increasing the spot size to 1.6-1.8 µm, the RBE decreased but was still higher than for homogeneously distributed protons. By further increasing the spot size to 2.7-2.8 µm, the RBE was no longer different from the homogeneous radiation. Our experiments demonstrate that varying spot size of low-LET radiation gradually modifies the RBE. This underlines that a substantial fraction of enhanced RBE originates from inhomogeneous energy concentrations on the µm scale (mean intertrack distances of low-LET particles below 0.1 µm) and quantifies the link between such energy concentration and RBE. The missing fraction of RBE enhancement when comparing with high-LET ions is attributed to the high inner track energy deposition on the nanometer scale. The results are compared with model results of PARTRAC and LEM for chromosomal aberration and cell survival, respectively, which suggest mechanistic interpretations of the observed radiation effects.

Structure probing by holographic imaging at nanometer scale with X-ray lasers (SPHINX)

The SPHINX project aims generating femtosecond-exposure X-ray holograms of microscopic samples and of their internal parts with nanometer resolution. The application is based on a new implementation of the phase-contrast holography that overcomes the main limitations encountered in the current systems (most based on absorption-contrast), namely the low energy range, the limited detector granularity and the weak illumination. The combination of polycapillary lenses, large X-Ray CCD arrays with small pixel size and XFEL sources allows splitting the beam, focusing, magnification and phase-contrast imaging in the keV energy range. Due to the wavelength-dependent optical behavior of the samples, the refractive diffraction reduces the diffraction limit together with a fast drop of the characteristic angles, both essential for the resolving power (given the limited X-ray detector pitch), while also eliminating the shadow effect and giving access to full structure probing. The key parameters are defined by the focusing optics, which could be, according to the beam and sample sizes, a polycapillary micro semi-lens or a combination of the former with a parabolic monocapillary. The advantage of “non-perfect” optics (not providing a point-like focus) is their divergence, driven mostly by the single waveguide. This allows sending on the same detector area the diverging object and reference beams (Fresnel configuration), both provided by a single optical element, condition unreachable with a Fresnel lens or a crystal mirror. Moreover, the femtosecond exposure time on X-FELs permits holographic reconstruction of in-vivo cell elements, viruses and nanorobotic devices during ultrafast molecular processes, yet unexplored by imaging techniques.

Identification of a descriptive beam size metric for complex beam shapes

Traditionally, in laser processing, simple beam profiles such as Gaussian beam profiles or top-hat profiles have been widely used. Recently, more complex beam shapes have been theorised. A common question remains: which factors affect the process most significantly? The size of the laser beam or its energy distribution – and how can the size of a complex beam shape be defined? In this work, Rosenthal-style calculations are used to calculate the conduction-mode temperature fields resulting from various laser beam shapes. Commonly used methods are used to calculate the beam size, such as the second moment method and the 1/e2 method, correlating them with calculated melt pool dimensions. Using these methods, we investigate whether a single beam size metric is sufficient to provide insights into conduction-mode laser processing.