In our previous investigation of the excited-state Raman spectra of free flavin mononucleotide (FMN) and the light-oxygen-voltage (LOV) sensitive protein EL222, we observed intensity variations and a red shift in the N1-C2 stretching modes within the S1 state Raman spectroscopy of EL222. This phenomenon was attributed to potential S1/S2 state mixing. However, the existence of T1/T2 mixing in EL222 remained undetermined. To address this, we employed an avoided crossing model to simulate the influence of electronic state mixing on Raman spectroscopy. Our results indicate that mixing induces redshift or blueshift in the 0-1 Raman transition frequency and alters the equilibrium position, consequently affecting the corresponding Raman intensity. The analysis further suggests that S1/S2 state mixing in EL222 occurs within the weak coupling regime. Additionally, experimental data revealed potential Raman signatures indicative of T1/T2 mixing in EL222.

INTRODUCTION:Bacterial endospores are highly resistant to environmental stressors. Their resistance complicates sterilization efforts, leading to exploration of novel inactivation techniques. Radiation in the water window spectral range (284-543 eV), typically studied using synchrotron sources, offers high contrast for bio-imaging and potential for efficient spore inactivation due to its high absorption and shallow penetration. METHODS:A compact pulsed laser-plasma soft X-ray source was used to irradiate Bacillus subtilis spores in the water window spectral range. A combination of STEM-EDS and Geant4 Monte Carlo simulations provided data on spore geometry, elemental composition, and dose deposition. The spores were deposited on glass coverslips, dried, irradiated in vacuum, and resuspended for viability testing. Spore survival was assessed via colony-forming units, and the survival curve was fitted with a modified biphasic model. RESULTS:The decimation dose (D10) was reached in less than one second at a 10 Hz repetition rate, indicating high inactivation efficiency. Effective photoabsorption coefficients were calculated from simulations and validated against tabulated values. Average dose rates in the spore core reached 2.4 kGy·s-1, with peak values exceeding 1011 Gy·s-1. The survival curve exhibited biphasic kinetics with saturation behavior due to spore clustering. DISCUSSION:The study confirms that soft X-rays in the water window range are highly effective in rapidly inactivating bacterial spores. The efficiency is attributed to the spectral region's short attenuation lengths and high absorption cross-sections, aligning with data from conventional ionizing sources.

Excellent radiation hardness and time-position properties are required for future tracking systems at the High-Luminosity Large Hadron Collider (HL-LHC) or even beyond that in proposed experiments at the Future Circular Hadron Collider (FCC-hh). One of the very promising technologies is 3D pixel silicon sensors. In contrast to planar detectors, they were designed with n+ and p+ columns etched through the bulk, minimizing charge drift distance and improving timing. However, the peculiar geometry and electrode configuration of these sensors create non-uniformities in both the internal electric field and the weighting field, resulting in a broader time-walk and compromising the sensor’s time resolution. The complex three-dimensional distribution of electrodes and sensitive detector volumes presents significant challenges for detailed microscopic characterization of charge transport properties, which is indispensable for architecture optimization. Here, we present the first study allowing for the generation of comprehensive 3D mappings of timing parameters across the 3D pixel sensors volume. The micrometer spatial resolution was obtained by using laser-based transient current technique (TCT) with two-photon absorption (TPA). Two prototypic detectors with alternative electrode configurations, quadratic and hexagonal, have been examined and compared.

It remains uncertain whether excited electronic state mixing occurs in the flavin cofactor of the light-oxygen-voltage-sensing (LOV) domain. In this study, we present transient absorption and femtosecond stimulated Raman spectra of both free and EL222 binding flavin mononucleotide (FMN). We observed a change in the shape of the excited-state absorption around 800 nm in the S1 state transient absorption after binding to EL222, alongside a relative intensity increase of the N1-C2 and C2═O2 stretching modes in the S1 state Raman spectra. Based on the previous calculated geometric differences between the ππ* and nπ* states, we propose a probable electronic state mixing in EL222 binding FMN. This mixing is favored by the nonsymmetric hydrogen bonding interaction between the flavin O4 atom and the asparagine residue and fewer hydrogen bonds with the O2 atom in EL222.

This paper describes performance enhancement developments to a closed-loop pump-driven wire-guided flow jet (WGJ) for ultrafast X-ray spectroscopy of liquid samples. Achievements include dramatically improved sample surface quality and reduced equipment footprint from 7 × 20 cm2 to 6 × 6 cm2, cost, and manufacturing time. Qualitative and quantitative measurements show that micro-scale wire surface modification yields significant improvements to the topography of the sample liquid surface. By manipulating their wettability, it is possible to better control the liquid sheet thickness and to obtain a smooth liquid sample surface, as demonstrated in this work.

Ultra-short electron beams are used as ultra-fast radiation source for radiobiology experiments aiming at very high energy electron beams (VHEE) radiotherapy with very high dose rates. Laser plasma accelerators are capable of producing electron beams as short as 1 fs and with tunable energy from few MeV up to multi-GeV with compact footprint. This makes them an attractive source for applications in different fields, where the ultra-short (fs) duration plays an important role. The time dynamics of the dose deposited by electron beams with energies in the range 50-250 MeV have been studied and the results are presented here. The results set a quantitative limit to the maximum dose rate at which the electron beams can impart dose.

X-ray spectroscopy is a demanded tool across multiple user communities. Here we report on a new station for X-ray emission spectroscopy at the Extreme Light Infrastructure Beamlines Facility. The instrument utilizes the von Hamos geometry and works with a number of different sample types, notably including liquid systems. We demonstrate a simple and reliable method for source position control using two cameras. This approach addresses energy calibration dependence on sample position, which is a characteristic source of measurement uncertainty for wavelength dispersive spectrometers in XES arrangement. We also present a straightforward procedure for energy calibration of liquid and powder samples to a thin film reference. The developed instrumentation enabled us to perform the first experimental determination of the Kα lines of liquidized K3Fe(CN)6 as well as powdered and liquidized FeNH4(SO4)2. Finally, we report on proof-of-principle use of a colliding jet liquid sample delivery system in an XES experiment.

A feasibility study conducted at the laser facility ELI Beamlines confirms that fs-laser pulses can produce Single Event Effect (SEE), Single Event Upset (SEU) and Single Event Burnout (SEB) conditions in irradiated Low Gain Avalanche Detectors (LGADs) and the corresponding PIN diodes. A comprehensive and systematic study on PIN and LGAD mortality has been conducted to experimentally determine the stability, instability, and irreversible damage thresholds for LGADs and PINs exploiting a fs-laser system. Thresholds are given as sets of two parameters: bias voltage and laser pulse energy (energy deposition threshold). Using the Two-Photon Absorption (TPA) - Transient Current Technique (TCT) to study the mechanism that triggers SEU/SEB conditions in LGADs, as a function of illumination position establishes this technique as a promising tool for more advanced explorations of SEE, not only in LGADs but also in other Si-based sensors. To achieve these results, a highly flexible and versatile fs-laser-based TCT experimental setup has been developed at ELI Beamlines, allowing two TCT modalities with the same setup: Single Photon Absorption (SPA) at 800 nm laser wavelength and TPA at 1550 nm.

The development of ultra-intense electron pulse for applications needs to be accompanied by the implementation of a practical dosimetry system. In this study four different systems were investigated as dosimeters for low doses with a very high-dose-rate source. First, the effects of ultra-short pulses were investigated for the yields of the Fricke dosimeter based on acidic solutions of ferrous sulfate; it was established that the yields were not significantly affected by the high dose rates, so the Fricke dosimeter system was used as a reference. Then, aqueous solutions of three compounds as fluorescence chemical dosimeters were utilized, each operated at a different solution pH: terephthalic acid - basic, trimesic acid - acidic, and coumarin-3-carboxylic acid (C3CA) - neutral. Fluorescence chemical dosimeters offer an attractive alternative to chemical dosimeters based on optical absorption for measuring biologically relevant low doses because of their higher sensitivity. The effects of very intense dose rate (TGy/ s) from pulses of fast electrons generated by a picosecond linear accelerator on the chemical yields of fluorescence chemical dosimeters were investigated at low peak doses (<20 Gy) and compared with yields determined under low-dose-rate irradiation from a 60 Co gamma-ray source (mGy/s). For the terephthalate and the trimesic acid dosimeters changes in the yields were not detected within the estimated (∼10%) precision of the experiments, but, due to the complexity of the mechanism of the hydroxyl radical initiated reactions in solutions of the relevant aromatic compounds, significant reductions of the chemical yield (–60%) were observed when the C3CA dosimeter was irradiated with the ultra-short pulses.

Gain suppression effects and destructive events caused by highly energetic single particles should be considered for the operation of LGADs in experiments. The performance of the LGADs depends on the particle's ionization density (energy loss) as well as incident angle, while large deposits of energy in the active zone of LGADs operated at high bias voltages can lead to the destructive break down of the sensor. Herein, we summarize the main findings from a study at the ELI Beamlines laser facility and from an ionized dense charge induced gain suppression (GS) study using a nuclear microbeam probe station and MeV ions at Ruder Boskovic Institute (RBI). The transient currents technique (TCT) with a fs-laser has been used for the SEB study, while the Ion Beam Induced Charge (IBIC) technique has been employed for the GS study.

Steady-state and transient absorption spectra with <50 fs time resolution were obtained for two conjugated polymers, both with ≈200 conjugated double bonds (N), constrained in planar, stable, polyene frameworks. Solutions of the polymers exhibit the same S2 → S1 → S* → S0 decay pathway observed for the N = 11-19 polyene oligomers and for zeaxanthin homologues with N = 11-23. Comparisons with the excited state dynamics of polydiactylene and a much longer, more disordered polyene polymer (poly(DEDPM)) show that the S2, S1, and S* lifetimes of the four polymers are almost identical. The S* signals in the polymers are assigned to absorption from vibrationally excited ground states. In spite of significant heterogeneities and variations in conjugation lengths in these long polyenes, their S0 → S2 absorptions are vibronically-resolved in room temperature solutions with electronic origins at ≈600 nm. The limiting wavelength for the S0 → S2 transitions is consistent with the persistence of bond length alternation in the electronic ground states and a HOMO-LUMO band gap in polyenes with N ≈ 200. The coincidence of the well-resolved S0 → S2 electronic origins and the convergence of the excited state lifetimes in the four polymers point to a common, "nearly infinite" polyene limit.

The orange carotenoid protein (OCP) is a structurally and functionally modular photoactive protein involved in cyanobacterial photoprotection. Recently, based on bioinformatic analysis and phylogenetic relationships, new families of OCP have been described, OCP2 and OCPx. The first characterization of the OCP2 showed both faster photoconversion and back-conversion, and lower fluorescence quenching of phycobilisomes relative to the well-characterized OCP1. Moreover, OCP2 is not regulated by the fluorescence recovery protein (FRP). In this work, we present a comprehensive study combining ultrafast spectroscopy and structural analysis to compare the photoactivation mechanisms of OCP1 and OCP2 from Tolypothrix PCC 7601. We show that despite significant differences in their functional characteristics, the spectroscopic properties of OCP1 and OCP2 are comparable. This indicates that the OCP functionality is not directly related to the spectroscopic properties of the bound carotenoid. In addition, the structural analysis by X-ray footprinting reveals that, overall, OCP1 and OCP2 have grossly the same photoactivation mechanism. However, the OCP2 is less reactive to radiolytic labeling, suggesting that the protein is less flexible than OCP1. This observation could explain fast photoconversion of OCP2.

Flavin mononucleotide (FMN) belongs to the large family of flavins, ubiquitous yellow-coloured biological chromophores that contain an isoalloxazine ring system. As a cofactor in flavoproteins, it is found in various enzymes and photosensory receptors, like those featuring the light-oxygen-voltage (LOV) domain. The photocycle of FMN is triggered by blue light and proceeds via a cascade of intermediate states. In this work, we have studied isolated FMN in an aqueous solution in order to elucidate the intrinsic electronic and vibrational changes of the chromophore upon excitation. The ultrafast transitions of excited FMN were monitored through the joint use of femtosecond stimulated Raman spectroscopy (FSRS) and transient absorption spectroscopy encompassing a time window between 0 ps and 6 ns with 50 fs time resolution. Global analysis of the obtained transient visible absorption and transient Raman spectra in combination with extensive quantum chemistry calculations identified unambiguously the singlet and triplet FMN populations and addressed solvent dynamics effects. The good agreement between the experimental and theoretical spectra facilitated the assignment of electronic transitions and vibrations. Our results represent the first steps towards more complex experiments aimed at tracking structural changes of FMN embedded in light-inducible proteins upon photoexcitation.

Formation yields of ˙OH radicals were precisely determined in aqueous solutions of coumarin-3-carboxylic acid and ferrous sulfate (i.e., Fricke dosimeter) exposed to 253.7 nm radiation delivered from a continuous source. Quantum yield of ˙OH radicals was determined as ∼0.08, i.e., roughly one out of twelve photons, efficiently absorbed in UV-illuminated solutions, produced one ˙OH radical. Energetically, a water molecule should undergo a correlated action of at least two 4.9 eV photons delivering enough energy for direct H-OH dissociation (5.0-5.4 eV). We suggest a mechanism based on an interaction of two water molecules, both in long-living triplet states. An intermolecular transfer of excitation energy provided a sufficient amount of energy for the dissociation of one water molecule into ˙OH and H˙ radicals. In an aqueous solution of phospholipids, quantum yields of hydroperoxides formed under these irradiation conditions decreased with total effectively absorbed energy (i.e. a dose), similar to the radiation chemical yields obtained during an exposure to ionizing radiation, such as gamma rays from radionuclide sources. Under 253.7 nm irradiation, one ˙OH radical causes a peroxidation of 34 phospholipid molecules. This implicates chain mechanism of the reaction.

An irreversible response of inorganic scintillators to intense soft xray laser radiation was investigated at the FLASH (Free-electron LASer in Hamburg) facility.Three ionic crystals, namely, Ce:YAG (cerium-doped yttrium aluminum garnet), PbWO 4 (lead tungstate), and ZnO (zinc oxide), were exposed to single 4.6 nm ultra-short laser pulses of variable pulse energy (up to 12 μJ) under normal incidence conditions with tight focus.Damaged areas produced with various levels of pulse fluences, were analyzed on the surface of irradiated samples using differential interference contrast (DIC) and atomic force microscopy (AFM).The effective beam area of 22.2 ± 2.2 μm 2 was determined by means of the ablation imprints method with the use of poly(methyl methacrylate) -PMMA.Applied to the three inorganic materials, this procedure gave almost the same values of an effective area.The single-shot damage threshold fluence was determined for each of these inorganic materials.The Ce:YAG sample seems to be the most radiation resistant under the given irradiation conditions, its damage threshold was determined to be as high as 660.8 ± 71.2 mJ/cm 2 .Contrary to that, the PbWO 4 sample exhibited the lowest radiation resistance with a threshold fluence of 62.6 ± 11.9 mJ/cm 2 .The threshold for ZnO was found to be 167.8± 30.8 mJ/cm 2 .Both interaction and material characteristics responsible for the damage threshold difference are discussed in the article.

The radiolytic changes in oxidation state for solutions of initially Np(V) and/or Np(VI) were investigated by gamma-irradiation in conjunction with UV/Vis spectroscopy of the aqueous phase. Samples were irradiated in varying concentrations of nitric acid, and with or without the presence of 30 % TBP in dodecane. At short irradiation times Np(V) was oxidized to Np(VI), even in the presence of the organic phase. Upon the radiolytic production of sufficient amounts of nitrous acid, reduction of Np(VI) to Np(V) occurred in both phases. This was accompanied by stripping of the previously extracted Np(VI). Nitric acid concentrations of 6 M mitigated this reduction.

In the framework of the ELI-Beamlines project, the HELL (High energy ELectron by Laser) platform will host an electron beamline with a dual aim: to explore innovative concepts of laser driven electron acceleration and to deliver a stable and reliable electron beam to external users, according to their specific needs. Because of this, it is crucial to identify the possible applications and their respective range of parameters. In order to accomplish this goal, Monte Carlo simulations of electron radiography and radiotherapy are performed and discussed. Once identified those parameter spaces, a beam transport line is studied and presented for each energy range. Finally, beam diagnostics are discussed.

We present the current status of ELI-Beamlines that will be the Czech pillar of the ELI (Extreme Light Infrastructure) project. The facility will make available high-brightness multi-TW ultrashort laser pulses at kHz repetition rate, 10 Hz repetition rate laser pulses at the petawatt level together with kilojoule nanosecond laser pulses that will be used for generation of 10 PW. These beamlines will be combined to generate X-ray secondary sources, to accelerate electrons, protons and ions and to study dense plasma and high-field frontier physics. These programs will be introduced together with the engineering program necessary for building a users' facility.

The redox chemistry of neptunium in irradiated 4 M nitric acid was investigated using gamma-ray irradiation and UV/Vis spectroscopic measurements. Irradiation caused changes in the abundances of Np(V) and Np(VI) regardless of the initial fractional components of these oxidation states. At low absorbed doses Np(V) was oxidized to Np(VI) in irradiated solution, due to its reaction with oxidizing, radiolytically-produced, free radicals. However, when sufficient radiolytically-produced nitrous acid accumulated, the reduction of Np(VI) to Np(V) occurred, even at this high nitric acid concentration. Neptunium(IV) was not produced. A kinetic model which incorporates the standard water radiolysis reactions, estimated radical yields for 4 M HNO3, and rate constants for neptunium reactions available from the literature was used to successfully reproduce the experimental results.