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A novel differential laser-induced thermoelastic spectroscopy (D-LITES) was demonstrated. In D-LITES, one probe and one control laser beam with different modulation phases were combined to generate two quartz tuning fork (QTF) mechanical oscillations, which are pi out of phase. The powers of the two lasers were adjusted to balance out the background noise. The differential signal was acquired by demodulating the QTF piezoelectric signal. The D-LITES sensor had a compact and cost-effective one-path configuration and was able to realize dualgas detection. Carbon dioxide (CO2) and methane (CH4) were chosen as target gases to verify the D-LITES sensor performance. With the D-LITES technique, the background noise was greatly suppressed. The minimum detection limit (MDL) was improved by 9 times from 260 ppm to 29 ppm and 7.13 times from 0.385 ppm to 0.054 ppm for CO2 and CH4 detection, respectively., QC 20240912

The accuracy of composition measurements by atom probe tomography is often dependent on the selected operation mode as well as the applied measurement parameters. The detected hit characteristics, distinguishing between single and multiple events, along with the electric field, are also affected by parameter selection. In this study, atom probe tomography experiments were performed on a stoichiometric TiN coating in voltage as well as in laser-assisted mode with systematically varied laser pulse energies. The observed elemental compositions were compared with complementary ion beam analysis measurements. The influence of multiple detection events was investigated by two approaches: I) A modified local electrode served as a hardware filter, reducing multiple detection events from 78.8 % to 41.9 % and from 40.9 % to 5.6 % using voltage mode and laser-assisted APT (0.6 nJ), respectively, and II) unfiltered datasets were analyzed by data post processing. The latter allowed the study of ion species, particularly of emerging complex molecular ions associated with dissociation processes. Additionally, average electric fields were estimated and spatial considerations were made to investigate the evolution of charge state ratios and hit characteristics during the measurement. Filtering the measurements significantly improved the elemental accuracy. In voltage mode, hardware and software filtering reduced the discrepancy between reference and observed composition from 3.8 at.% to 2.1 at.% and 0.1 at.% within uncertainty limits. In laser-assisted mode, higher laser pulse energy increased the difference between unfiltered data and the reference composition, from 1.4 at.% (0.1 nJ) to 8.1 at.% (2.0 nJ). Ion species analysis of the datasets shows an increasing presence of complex ions (Ti2N) with raising laser pulse energy. Electric field studies reveal a decline from 40 V/nm in voltage mode to 36 V/nm applying a high laser pulse energy of 2.0 nJ, indicating insufficient field str

We report results from a study of the local structure of hydrated nanocrystalline 2 m films of the well known proton conductor BaZr1-xScxO3-x/2 with x = 0.45, 0.54 and 0.64, using infrared (IR) spectroscopy. The films were prepared by magnetron sputtering. Analysis of the IR spectra focused on the O–H stretching region (2000—3700 cm-1), which reveals the presence of several distinct O–H stretching bands for which the intensity and frequency of each band vary in an unsystematic manner with Sc concentration. The spectra for the two higher Sc concentrations, x = 0.54 and 0.64, exhibit a distinct, highly intense O–H stretching band centered at around 3400–3500 cm-1, which is assigned to relatively symmetric, weakly hydrogen-bonding, proton configurations. The spectrum for the lower Sc concentration, x = 0.45, does not feature such a band but a broader, weaker, O–H stretching band between approximately 2500 and 3700 cm-1, suggesting that the protons are more homogeneously distributed over a range of different local proton coordinations in this relatively weakly doped material. A comparison to the IR spectra of powder samples of similar compositions suggests that for x = 0.45, the spectra and proton coordination of films and powder samples are similar, whereas for x = 0.54 and 0.64, a larger fraction of protons seems to be located in weakly hydrogen-bonding proton configurations in the films compared to the respective powder samples.

We describe a method to compute photon–matter interaction and atomic dynamics with x-ray lasers using a hybrid code based on classical molecular dynamics and collisional-radiative calculations. The forces between the atoms are dynamically determined based on changes to their electronic occupations and the formation of a free electron cloud created from the irradiation of photons in the x-ray spectrum. The rapid transition from neutral solid matter to dense plasma phase allows the use of screened potentials, reducing the number of non-bonded interactions. In combination with parallelization through domain decomposition, the hybrid code handles large-scale molecular dynamics and ionization. This method is applicable for large enough samples (solids, liquids, proteins, viruses, atomic clusters, and crystals) that, when exposed to an x-ray laser pulse, turn into a plasma in the first few femtoseconds of the interaction. We present four examples demonstrating the applicability of the method. We investigate the non-thermal heating and scattering of bulk water and damage-induced dynamics of a protein crystal using an x-ray pump–probe scheme. In both cases, we compare to the experimental data. For single particle imaging, we simulate the ultrafast dynamics of a methane cluster exposed to a femtosecond x-ray laser. In the context of coherent diffractive imaging, we study the fragmentation as given by an x-ray pump–probe setup to understand the evolution of radiation damage in the time range of hundreds of femtoseconds.

The Joint European Torus (JET) has recently conducted its second deuterium-tritium (DT) experimental campaign DTE2, providing unique opportunity for studying both physics and engineering aspects of nuclear fusion plasmas. This also allowed the exploitation of new diagnostics and technologies that were not available during the first JET DT campaign held in 1997. Among these new instruments, the enhancement projects of the JET nuclear diagnostics lead to the development and installation of synthetic single crystal diamond detectors along different collimated line of sights. This paper describes the single crystal diamond-based diagnostic suite of the JET tokamak and the enhanced 14 MeV neutron diagnostic capabilities in terms of neutron yield and high resolution neutron spectroscopy. The diamond characterization measurements and the calibration procedure at JET are shown, together with performance of the diamond based neutron spectrometer as 14 MeV neutron yield monitor which allows the separation of 2.5 MeV and 14 MeV neutrons in trace tritium plasmas. The first high-resolution 14 MeV neutron spectroscopy measurements in neutral beam injection-heated DT plasmas are presented, allowing thermal and non-thermal neutron component separation. Prospects for the diagnose of DT burning plasmas such as ITER and SPARC will be presented.

QC 20240321

The ForMAX beamline at the MAX IV Laboratory provides multiscale and multimodal structural characterization of hierarchical materials in the nanometre to millimetre range by combining small- and wide-angle X-ray scattering with full-field microtomography. The modular design of the beamline is optimized for easy switching between different experimental modalities. The beamline has a special focus on the development of novel fibrous materials from forest resources, but it is also well suited for studies within, for example, food science and biomedical research., QC 20240325

We present a tunable (6.62-11.34 µm), singly-resonant, cascade optical parametric oscillator with intracavity pumping of BaGa2GeSe6 in the second stage and spectral narrowing realized by a Volume Bragg Grating acting on the signal wave of the first stage which serves as a pump for the second stage. The maximum energy achieved near 8 µm in the narrowband regime is 1.1 mJ at 100 Hz (spectral width: ∼20 cm−1, pulse duration: ∼7 ns). The overall conversion efficiency from 1 to 8 µm for broadband and narrowband operation is 4.0% and 3.1%, respectively, corresponding to quantum efficiencies of 31% and 23%., QC 20240202

This study focuses on enhancing the accuracy of hydrogen content verification in hydrogen-rich ultrathin materials relevant for sustainable energy applications. Ion beams are used for distinctive real-space detection leveraging elastic and inelastic interactions with hydrogen atoms. However, the lack of experimental reference data on electronic interactions poses a challenge to the accuracy of analytical techniques. We investigate the effect of absorbed hydrogen on the electronic energy deposition of 15N-ions in amorphous transition metal compounds, specifically V and Zr, covering concentrations >1H/M. Employing resonant nuclear reactions and Rutherford backscattering, the energy loss is found to increase considerably with hydrogen content, in line with Bragg's additivity. The electronic energy loss cross section for 15N-ions at 6.5 MeV measured (64.55±3.38) eV cm2/1015 atoms. Results are compared to semi-empirical and theoretical models. The findings improve hydrogen profiling accuracy using 15N-nuclear reaction analysis and enable unprecedented methods for hydrogen quantification by other, commonly available ion beams.

Excited state molecular dynamics simulations of the photoexcited phenyl azide have been performed. The semi-classical surface hopping approximation has enabled an unconstrained analysis of the electronic and nuclear degrees of freedom which contribute to the molecular dissociation of phenyl azide into phenyl nitrene and molecular nitrogen. The significance of the second singlet excited state in leading the photodissociation has been established through electronic structure calculations, based on multi-configurational schemes, and state population dynamics. The investigations on the structural dynamics have revealed the N−N bond separation to be accompanied by synchronous changes in the azide N−N−N bond angle. The 100 fs simulation results in a nitrene fragment that is electronically excited in the singlet manifold.

Resonant inelastic x-ray scattering (RIXS) is a major method for investigation of electronic structure and dynamics, with applications ranging from basic atomic physics to materials science. In RIXS applied to inversion-symmetric systems, it has generally been accepted that strict parity selectivity applies in the sub-kilo-electron volt region. In contrast, we show that the parity selection rule is violated in the RIXS spectra of the free homonuclear diatomic O2 molecule. By analyzing the spectral dependence on scattering angle, we demonstrate that the violation is due to the phase difference in coherent scattering at the two atomic sites, in analogy with Young's double-slit experiment. The result also implies that the interpretation of x-ray absorption spectra for inversion symmetric molecules in this energy range must be revised., QC 20240229

In this study, we compare the two prominent Light Detection and Ranging (LIDAR) technologies: Frequency Modulated Continuous Wave (FMCW) and Time of Flight (ToF). By constructing a setup capable of performing both LIDAR methods at the single photon level using a Superconducting Nanowire Single Photon Detector (SNSPD), we compare the accuracy and investigate the dependence of the resulting images and accuracy on the signal power and the corresponding signal to noise ratio. We demonstrate that both LIDAR methods are able to reconstruct 3D environments with a signal-to-noise ratio as low as 0.03. However, the accuracy of FMCW LIDAR is shown to degrade in the low photon regime, while ToF LIDAR accuracy is shown to be stable across the same range. Lastly, we use a median de-noising convolution filter to effectively combat the typical "salt and pepper" noise found in LIDAR images, further enhancing the performance of both methods., QC 20240314

We present time-resolved X-ray absorption spectra of ionized liquid water and demonstrate that OH radicals, H3O+ ions, and solvated electrons all leave distinct X-ray-spectroscopic signatures. Particularly, this allows us to characterize the electron solvation process through a tool that focuses on the electronic response of oxygen atoms in the immediate vicinity of a solvated electron. Our experimental results, supported by ab initio calculations, confirm the formation of a cavity in which the solvated electron is trapped. We show that the solvation dynamics are governed by the magnitude of the random structural fluctuations present in water. As a consequence, the solvation time is highly sensitive to temperature and to the specific way the electron is injected into water.

Three-dimensional (3D) micro-nano fabrication through two-photon polymerization (TPP) is a prominent approach for fabricating complex 3D structures. However, the existing techniques face limitations, such as small fabrication area, dependence on high numerical aperture (e.g., oil immersion) objective lenses, which are more expensive. We developed a 780 nm fs laser system integrated with a 2D galvanometer system and Z axis to create a 3D micro-nano printing system. A method to print arbitrarily complex 3D structures while maintaining an extremely high lateral spatial resolution of sub-100nm is proposed by using a cheap low numerical aperture objective lens with the laser power and exposure time precisely controlled. The impact of the laser power and exposure time on the resolution of 3D micro-nano processing is investigated, and we identify the optimal processing environment for achieving the best resolution. The printed linewidth of 62 nm was achieved without the use of an oil immersed objective lens, and only one laser beam was used instead of stimulated emission depletion. Microneedle arrays for animal injection were fabricated using this strategy, which can improve the performance of animal organoid repair. Our results suggest that TPP micro-nano fabrication is an effective method for processing microneedle arrays for biomedical engineering, with the ability to improve the processing resolution with a cheap low numerical aperture objectives lens (e.g., NA = 0.4) through meticulous control of laser power and exposure time. This approach opens up possibilities for affordable and scalable fabrication in sub-100nm structures., QC 20240301

Optical nanoscopy, also known as super-resolution optical microscopy, has provided scientists with the means to surpass the diffraction limit of light microscopy and attain new insights into nanoscopic structures and processes that were previously inaccessible. In recent decades, numerous studies have endeavored to enhance super-resolution microscopy in terms of its spatial (lateral) resolution, axial resolution, and temporal resolution. In this review, we discuss recent efforts to push the resolution limit of stimulated emission depletion (STED) optical nanoscopy across multiple dimensions, including lateral resolution, axial resolution, temporal resolution, and labeling precision. We introduce promising techniques and methodologies building on the STED concept that have emerged in the field, such as MINSTED, isotropic STED, and event-triggered STED, and evaluate their respective strengths and limitations. Moreover, we discuss trade-off relationships that exist in far-field optical microscopy and how they come about in STED optical nanoscopy. By examining the latest developments addressing these aspects, we aim to provide an updated overview of the current state of STED nanoscopy and its potential for future research., QC 20240122

In nonlinear microresonators with strong stimulated Raman scattering effect, it is difficult if not impossible to generate Kerr soliton microcombs with a small free spectral range (FSR) (< 100 GHz) due to the competition between the Raman and Kerr effects. In this article, we overcome this limitation by using odd-period photonic crystal microrings (PCMs). Numerical simulations on the silicon-on-insulator (SOI) PCM show that a small frequency shift (5 GHz) induced by the photonic crystal structure can moderately suppress the Raman effect, such that chaotic microcombs with a small FSR can be generated. With a larger frequency shift (e.g., >= 10 GHz), the Raman effect is significantly suppressed, and the soliton microcombs can be generated. For comparison, without the frequency shift, only Raman lasing can be achieved in a conventional microring. To investigate the applicability of the proposed method in other material platforms, we carried out simulations for the aluminium nitride (AlN) PCM. The results are comparable to those obtained on the SOI PCM. Our method opens a new approach to the generation of small FSR Kerr soliton microcombs in microresonators with strong Raman effect, which is important for expanding the available nonlinear platforms and applications such as telecommunications, radio-frequency photonics, and astronomical spectrographs., QC 20240201

The idea of using ultrashort X-ray pulses to obtain images of single proteins frozen in time has fascinated and inspired many. It was one of the arguments for building X-ray free-electron lasers. According to theory, the extremely intense pulses provide sufficient signal to dispense with using crystals as an amplifier, and the ultrashort pulse duration permits capturing the diffraction data before the sample inevitably explodes. This was first demonstrated on biological samples a decade ago on the giant mimivirus. Since then, a large collaboration has been pushing the limit of the smallest sample that can be imaged. The ability to capture snapshots on the timescale of atomic vibrations, while keeping the sample at room temperature, may allow probing the entire conformational phase space of macromolecules. Here we show the first observation of an X-ray diffraction pattern from a single protein, that of Escherichia coli GroEL which at 14 nm in diameter is the smallest biological sample ever imaged by X-rays, and demonstrate that the concept of diffraction before destruction extends to single proteins. From the pattern, it is possible to determine the approximate orientation of the protein. Our experiment demonstrates the feasibility of ultrafast imaging of single proteins, opening the way to single-molecule time-resolved studies on the femtosecond timescale., QC 20240125

Time-resolved X-ray photoelectron spectroscopy (TXPS) is a well-established technique to probe coherent nuclear wavepacket dynamics using both table-top and free-electron-based ultrafast X-ray lasers. Energy resolution, however, becomes compromised for a very short pulse duration in the sub-femtosecond range. By resonantly tuning the X-ray pulse to core-excited states undergoing Auger decay, this drawback of TXPS can be mitigated. While resonant Auger-electron spectroscopy (RAS) can recover the vibrational structures not hidden by broadband excitation, the full reconstruction of the wavepacket is a standing challenge. Here, we theoretically demonstrate how the complete information of a nuclear wavepacket, i.e., the populations and relative phases of the vibrational states constituting the wavepacket, can be retrieved from time-resolved RAS (TRAS) measurements. Thus, TRAS offers key insights into coupled nuclear and electronic dynamics in complex systems on ultrashort timescales, providing an alternative to leverage femtosecond and attosecond X-ray probe pulses., QC 20240115

Ever since the mid-1960’s, locking the phases of modes enabled the generation of laser pulses of duration limited only by the uncertainty principle, opening the field of ultrafast science. In contrast to conventional lasers, mode spacing in random lasers is ill-defined because optical feedback comes from scattering centres at random positions, making it hard to use mode locking in transform limited pulse generation. Here the generation of sub-nanosecond transform-limited pulses from a mode-locked random fibre laser is reported. Rayleigh backscattering from decimetre-long sections of telecom fibre serves as laser feedback, providing narrow spectral selectivity to the Fourier limit. The laser is adjustable in pulse duration (0.34–20 ns), repetition rate (0.714–1.22 MHz) and can be temperature tuned. The high spectral-efficiency pulses are applied in distributed temperature sensing with 9.0 cm and 3.3 × 10−3 K resolution, exemplifying how the results can drive advances in the fields of spectroscopy, telecommunications, and sensing., QC 20240115

This work describes a program for computing and analyzing the ultrafast (attosecond and femtosecond) nonlinear X-ray spectra of molecules at the multiconfigurational quantum chemistry level, called MCNOX. It is aimed at cutting-edge current and future photochemistry/photophysics applications enabled by X-ray free-electron lasers and high harmonic generation light sources. It can compute steady-state X-ray absorption spectroscopy (XAS) and three types of ultrafast nonlinear X-ray spectra: transient XAS, all-X-ray four-wave mixing, and stimulated Raman spectra. It is especially capable of picking out major electronic transitions, and further computing the natural transition orbitals for these transitions, which help finally yield the physical and chemical insights from complex signals. Following a research paradigm of "electronic structure-*molecular dynamics-*signal", in this paper, methods for the former two steps are reviewed, and then the theory, implementations, and technical details for signal simulations are presented along illustrative examples on uracil., QC 20240110

A procedure for automated low uncertainty assessment of empty cavity mode frequencies in Fabry-Pérot cavity based refractometry that does not require access to laser frequency measuring instrumentation is presented. It requires a previously well-characterized system regarding mirror phase shifts, Gouy phase, and mode number, and is based on the fact that the assessed refractivity should not change when mode jumps take place. It is demonstrated that the procedure is capable of assessing mode frequencies with an uncertainty of 30 MHz, which, when assessing pressure of nitrogen, corresponds to an uncertainty of 0.3 mPa.

The present study investigates the photofragmentation behavior of iodine-enhanced nitroimidazole-based radiosensitizer model compounds in their protonated form using near-edge X-ray absorption mass spectrometry and quantum mechanical calculations. These molecules possess dual functionality: improved photoabsorption capabilities and the ability to generate species that are relevant to cancer sensitization upon photofragmentation. Four samples were investigated by scanning the generated fragments in the energy regions around C 1s, N 1s, O 1s, and I 3d-edges with a particular focus on NO2+ production. The experimental summed ion yield spectra are explained using the theoretical near-edge X-ray absorption fine structure spectrum based on density functional theory. Born-Oppenheimer-based molecular dynamics simulations were performed to investigate the fragmentation processes.

The fast-ion phase-space distribution function in axisymmetric tokamak plasmas is completely described by the three constants of motion: energy, magnetic moment and toroidal canonical angular momentum. In this work, the observable regions of constants-of-motion phase-space, given a diagnostic setup, are identified and explained using projected velocities of the fast ions along the diagnostic lines-of-sight as a proxy for several fast-ion diagnostics, such as fast-ion D alpha spectroscopy, collective Thomson scattering, neutron emission spectroscopy and gamma-ray spectroscopy. The observable region in constants-of-motion space is given by a position condition and a velocity condition, and the diagnostic sensitivity is given by a gyro-orbit and a drift-orbit weighting. As a practical example, 3D orbit weight functions quantifying the diagnostic sensitivity to each point in phase-space are computed and investigated for the future COMPASS-Upgrade and MAST-Upgrade tokamaks.

Understanding “efficiency roll-off” (i.e., the drop in emission efficiency with increasing current) is critical if efficient and bright emissive technologies are to be rationally designed. Emerging light-emitting electrochemical cells (LECs) can be cost- and energy-efficiently fabricated by ambient-air printing by virtue of the in situ formation of a p-n junction doping structure. However, this in situ doping transformation renders a meaningful efficiency analysis challenging. Herein, a method for separation and quantification of major LEC loss factors, notably the outcoupling efficiency and exciton quenching, is presented. Specifically, the position of the emissive p-n junction in common singlet-exciton emitting LECs is measured to shift markedly with increasing current, and the influence of this shift on the outcoupling efficiency is quantified. It is further verified that the LEC-characteristic high electrochemical-doping concentration renders singlet-polaron quenching (SPQ) significant already at low drive current density, but also that SPQ increases super-linearly with increasing current, because of increasing polaron density in the p-n junction region. This results in that SPQ dominates singlet-singlet quenching for relevant current densities, and significantly contributes to the efficiency roll-off. This method for deciphering the LEC efficiency roll-off can contribute to a rational realization of all-printed LEC devices that are efficient at highluminance.

Biological structure determination has had new avenues of investigation opened due to the introduction of X-ray free-electron lasers (XFELs). These X-ray lasers provide an extreme amount of photons on ultrafast timescales used to probe matter, and in particular biomolecules. The high intensity of the X-rays destroys the sample, though not before structural information has been acquired. The unique properties of the probe provide the unprecedented opportunity to study the un-crystallized form of biological macromolecules, small crystals of biomolecules and their dynamics. In this work, we study processes in XFEL imaging experiments that could affect the achievable resolution of the protein structure in a diffraction experiment. Elastic scattering is the process which provides structural information and leaves the sample unperturbed. This interaction occurs far less often compared to damage inducing processes, such as photoabsorption, which leads to rapid ionization of the studied sample. By using density functional theory, we study the effect of ultrahigh charge states in small systems, such as amino acids and peptides, on the subsequent bond breaking and charge dynamics. Reproducible fragmentation patterns are studied in order to find features that could be understood in larger systems, such as proteins. Biomolecules are dynamical systems, and the currently used pulse duration is not short enough to outrun the movement of the atoms. The diffraction patterns acquired in an experiment are therefore an incoherent sum of slightly different conformations of the same system. Water can help to reduce these structural variations, but the water molecules themselves will then be a source of noise. Using classical molecular dynamics, we study the optimal amount of water that should be used to achieve the highest resolution. To simulate ultrafast molecular dynamics of larger systems such as proteins, we develop a hybrid Monte Carlo/molecular dynamics model. We utilize it to

We look into the problem of stochastic resetting with refractory periods. The model dynamics comprises diffusive and motionless phases. The diffusive phase ends at random time instants, at which the system is reset to a given position-where the system remains at rest for a random time interval, termed the refractory period. A pathway formulation is introduced to derive exact analytical results for the relevant observables in a broad framework, with the resetting time and the refractory period following arbitrary distributions. For the paradigmatic case of Poissonian distributions of the resetting and refractory times, in general with different characteristic rates, closed-form expressions are obtained that successfully describe the relaxation to the steady state. Finally, we focus on the single-target search problem, in which the survival probability and the mean first passage time to the target can be exactly computed. Therein, we also discuss optimal strategies, which show a non-trivial dependence on the refractory period.

Ultrafast Raman spectroscopy with attosecond pulses in the extreme ultraviolet and X-ray regime has been proposed theoretically for tracking the non-adiabatic dynamics of molecules in great detail. The large bandwidth of these pulses, which span several electronvolts within a couple of femtoseconds, provides a unique tool for tracking non-adiabatic phenomena. However, spectroscopy with classical light is limited by the time–bandwidth product of the probe laser pulse. In this work, we theoretically investigate an ultrafast Raman spectroscopy scheme that utilizes pairs of entangled photons. Our model simulations demonstrate that the dynamics in the vicinity of a conical intersection can be resolved with unprecedented resolution in the time and frequency domain.

The effect of Eu doping in the Tsai quasicrystal (QC) GdCd7.88 and its periodic 1/1 approximant crystal (AC) GdCd6 are investigated. This represents the first synthesis of Eu-containing stable QC samples, where three samples with the final composition Gd1-xEux Cd-7.6 +/-alpha at Eu doping concentrations x = 0.06, 0.13, and 0.19 are obtained (alpha similar to 0.2). They are compared to two 1/1 ACs with compositions Gd1-xEuxCd6 (x = 0.12, 0.16). In addition, a new type of 1/1 AC, differing only by the inclusion of extra Cd sites unique to the Eu4Cd25 1/1 AC, has been discovered and synthesized for the concentrations Gd1-xEuxCd6+delta (x = 0.25, 0.33, 0.45, 0.69, 0.73, and 0 < delta <= 0.085). Due to the preferred cube morphology of its single grains, we refer to them as c-type 1/1 ACs and to the conventional standard ones as s-type. In both QCs and s-type ACs, the Eu content appears to saturate at a concentration of similar to 20%. On the other hand, any Gd| Eu ratio is allowed in the c-type ACs, varying continuously between GdCd6 and Eu4Cd25. We describe and contrast the changes in composition, atomic structure, specific heat, and magnetic properties induced by Eu doping in the quasicrystalline phase and the s-type and c-type 1/1 ACs. By comparing our results to the literature data, we propose that the occupancy of the extra Cd sites can be used to predict the stability of Tsai-type quasicrystalline phases.

The mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (GRBs)1, sources of high-frequency gravitational waves (GWs)2 and likely production sites for heavy-element nucleosynthesis by means of rapid neutron capture (the r-process)3. Here we present observations of the exceptionally bright GRB 230307A. We show that GRB 230307A belongs to the class of long-duration GRBs associated with compact object mergers4,5,6 and contains a kilonova similar to AT2017gfo, associated with the GW merger GW170817 (refs. 7,8,9,10,11,12). We obtained James Webb Space Telescope (JWST) mid-infrared imaging and spectroscopy 29 and 61 days after the burst. The spectroscopy shows an emission line at 2.15 microns, which we interpret as tellurium (atomic mass A = 130) and a very red source, emitting most of its light in the mid-infrared owing to the production of lanthanides. These observations demonstrate that nucleosynthesis in GRBs can create r-process elements across a broad atomic mass range and play a central role in heavy-element nucleosynthesis across the Universe.

We theoretically propose a multidimensional high-harmonic echo spectroscopy technique which utilizes strong optical fields to resolve coherent electron dynamics spanning an energy range of multiple electronvolts. Using our recently developed semi-perturbative approach, we can describe the coherent valence electron dynamics driven by a sequence of phase-matched and well-separated short few-cycle strong infrared laser pulses. The recombination of tunnel-ionized electrons by each pulse coherently populates the valence states of a molecule, which allows for a direct observation of its dynamics via the high harmonic echo signal. The broad bandwidth of the effective dipole between valence states originated from the strong-field excitation results in nontrivial ultra-delayed partial rephasing echo, which is not observed in standard two-dimensional optical spectroscopic techniques in a two-level molecular systems. We demonstrate the results of simulations for the anionic molecular system and show that the ultrafast valence electron dynamics can be well captured with femtosecond resolution.

The mutual neutralization reaction in collisions of Li+ with CN− is a promising candidate for rigorous multi-dimensional ab initio studies of atom-molecule charge transfer processes. The reaction is driven by the non-adiabatic interaction between the lowest two 1A′ electronic states at large Li–CN distances, resulting in a large cross section for mutual neutralization. As a first step, the relevant adiabatic potential energy surfaces and non-adiabatic interaction are computed ab initio, and the process is studied quantum mechanically using the vibrational sudden approximation, where the vibrational and rotational motions of the CN molecule are assumed to be frozen during the collision.

Fullerenes and PAHs (polycyclic aromatic hydrocarbons) are two families of carbon based molecules. These are both present in the interstellar medium, and are there believed to play important roles in various processes, including the formation of stars in the case of PAHs. This thesis presents studies on the structures and dynamics of fullerenes and PAHs and their weakly bound clusters, that all have relevance in an astrophysical context. Here, the focus is on knockout driven reactions in which a single atom is knocked out of a molecule or a molecular cluster as a result of Rutherford-like scattering processes. These are modelled by means of classical molecular dynamics simulations. The first study investigates knockout processes where a C60 molecule is collided with helium atoms at 166 eV in the centre-of-mass-frame, similar to the velocities in interstellar shocks. Using a combination of experimental measurements and molecular dynamics simulations we find that highly reactive C59 fragments can be created sufficiently cold to stabilise and survive indefinitely inisolation. Following the first study, we model the structures and stabilities of mixed clusters of C60 and C24H12 (coronene) molecules. We find that the two molecular species do not mix very well, but that they like to be in compact formations. For larger pure coronene clusters, we find that the most stable clusters contain two interacting stacks, forming a shape that looks similar to a “handshake”. These results are consistent with earlier modelling studies. Here, we show that such stacks also show up as subclusters in large mixed clusters. Finally, we use the most stable clusters from the second study as targets in collisions with 3 keV argon atoms. We find that the simulated mass spectra strongly resemble the corresponding experimental ones. These show that many various forms of new molecular structures, both fragments and large new molecules, are being formed, as a result of the collisions. Here, the sim

Transition metal complexes that participate in homogeneous reactions often perform the role of a catalyst, facilitating novel reaction pathways. When these complexes are pushed away from their equilibrium, the arrangement of the coordinating ligands around the metal center is perturbed and new reaction pathways are opened. By using a light-induced “trigger” to push the metal complex away from its equilibrium, this process can be initiated with precision. This thesis is concerned with the theoretical understanding of light-induced “triggered” reactions that generate transient, short-lived photoproducts in solution, capable of reacting with the surrounding solvent medium. A combination of theoretical and experimental tools are employed to give precise information about the formation and decay of these transient photoproducts. In an effort to understand the innate differences between a broad range of transition metal complexes, electron configurations of the metal and its coordinating ligands are a natural starting point. These distinct electronic structures define the physical structure of the transition metal complex and explain the reactivity or lack of reactivity of the transition metal complex. To describe these electronic structures, robust quantum chemistry methods are required. Coinciding with these methods is a theoretical framework that aims to simulate the evolution of molecules by means of a molecular dynamics simulation. The present work involves the study of ironpentacarbonyl or Fe(CO)5 which we use to explain the reactive landscape of a broad class of carbonyl coordinated transition metal complexes. The part of the thesis devoted to Fe(CO)5 is divided into distinct sections (i) the short-time (femtosecond-to-picosecond) gas-phase excited state molecular dynamics that produces the transient species, (ii) the long-time (picosecond-to-nanosecond) liquid-phase ground state molecular dynamics which describes the intermediates formed by the transient species a

Small heavy particles in a fluid flow respond to the flow on a timescale proportional to their inertia or Stokes number St. Their behavior has been thought to be gradually modified as St increases. We show, on the other hand, in the steady spatially periodic laminar Taylor Green vortex flow, that particle dynamics, and their effective diffusivity, actually change in an irregular, nonmonotonic, and sometimes discontinuous manner with increasing St. At St similar to 1, we show chaotic particle motion, contrasting with earlier conclusions for heavy particles in the same flow [Wang et al., Phys. Fluids 4, 1789 (1992)]. Particles may display trapped orbits, or unbounded diffusive or ballistic dispersion, with the vortices behaving like scatterers in a soft Lorentz gas [Klages et al., Phys. Rev. Lett. 122, 064102 (2019)]. The dynamics is nonergodic.

This report describes a project performed at Linnaeus University with the task of solving the Schrodinger equation for electrons in homonuclear diatomic molecules, using the finite element method in Python. The Schrodinger equation is solved for the hydrogen atom, nitrogen atom, hydrogen molecule and nitrogen molecule using a finite element method. The results of the hydrogen atom showed a high accuracy compared to the analytical solution, given that the domain had high enough resolution. The solutions of the hydrogen molecule, nitrogen atom and nitrogen molecule showed reasonable accuracy although the resolution appeared sufficient. This foundation of Python code can be further built upon to explore more molecules and more properties, such as total energies and vibrational energies.

Quantum information technology is an emerging field with important applications such as quantum cryptography and teleportation, quantum imaging and lithography. These applications make use of single photons and pairs of entangled photons. In this work, we experimentally generate and attempt to detect the entangled photons. The entangled photon pairs are produced using a nonlinear crystal of beta bariumborate through a process of spontaneous parametric down-conversion (SPDC). Alignment necessary to detect the entangled photon pairs is implemented using a HeNe laser. The experimental results reveal key signatures of the down-converted photons: (i) energy conservation as the wave length of generated photons (810 nm) is two times larger than that of the photons used to optically pump SPDC (405 nm), which is shown by using a 10-nm band-pass filter centred around 810 nm; (ii) the angles between the two photons of a pair correspond to the configuration of momentum conservation calculated analytically;(iii) the photons arrived at the detectors within the jitter time of those; and (iv) orthogonal polarisation of down-converted photons (810 nm) with respect to pump photons (405 nm). These findings show the consequences of SPDC.

Naphthalimide derivatives composed of donor-acceptor type structures hold significant promise across a wide range of applications. Here, the solvent polarity and viscosity controlled excited-state dynamics of a naphthalimide derivative with a donor-acceptor structure were studied using multiple spectroscopic techniques. From the stationary spectroscopic investigations, large Stokes shift and low fluorescence quantum yield were observed with increasing the solvent polarity, suggesting a more polar excited state relative to the ground state, which is evidenced by the Lippert-Mataga relationship. We also observe an enhanced fluorescence with a prolonged lifetime in a more viscous solution due to the restriction of excited-state molecular rearrangement. These observations result from the emerged twisted intramolecular charge transfer (TICT) state. The ultrafast spectroscopy studies further unravel a solvent polarity dependent excited state evolution from the intramolecular charge transfer state to the TICT state, revealing that the TICT state can be populated only in strong polar solvents. Control experiments by tuning the solvent viscosity in ultrafast experiments were employed to verify the excited state molecular rearrangement subsequently. These observations collectively emphasize how fine-tuning the photophysical properties of naphthalimide derivatives can be achieved through strategic manipulation of solvent polarity and viscosity. The TICT mechanism of naphthalimide derivative was investigated by ultrafast spectroscopy, unraveling the dielectronic constant controlled excited state evolution from LE/ICT to the TICT state accompanied by the molecular rearrangement.

In this thesis, reactive scattering processes involving the H2 reaction complex are studied ab initio and fully quantum mechanically. These processes have in common that they involve highly excited electronic states, which could be either bound or resonant. Non-adiabatic couplings, which can be significant both at small and large internuclear distances, need to be included to account for the interaction between the bound electronic states. In addition, the electronic resonant states interact with the ionization continuum at small internuclear distances, which may cause the collision complex to autoionize. In this work, a model is developed which incorporates these different coupling mechanisms. By introducing a quasidiabatic model at small internuclear distances, resonant states and couplings to the ionization continuum are incorporated. The quasidiabatic model is combined with a strict diabatic description, which rigorously incorporates non-adiabatic couplings among the bound electronic states. Nuclear dynamics are solved for using a close-coupling approach in a strict diabatic representation, where a non-local complex potential is included to account for loss into the ionization continuum. With this model, various reactive scattering processes can systematically be studied using the same set of potential energy curves and couplings. The model is applied in studies of H++H- mutual neutralization, H(1s)+H(ns) and H++H- associative ionization as well as dissociative recombination and resonant ion-pair formation in electron collisions with HD+. Cross sections and branching ratios are compared with results from previous experiments and theoretical studies.

Conical intersections are known to play a vital role in many photochemical processes. The breakdown of the Born–Oppenheimer approximation in the vicinity of a conical intersection causes exciting phenomena, such as the ultrafast radiationless decay of excited states. The passage of a molecule through a conical intersection creates a coherent superposition of electronic states via nonadiabatic couplings. Detecting this coherent superposition may serve as a direct probe of the conical intersection. In this paper, we theoretically demonstrate the use of coherent spontaneous emission in samples with long-range order for probing the occurrence of a conical intersection in a molecule. Our simulations show that the spectrum contains clear signatures of the created coherent superposition of electronic states. We investigate the bandwidth requirements for the x-ray probes, which influence the observation of coherent superposition generated by the conical intersection.

This thesis presents experimental studies of mutual-neutralization reactions between H- and the cations 7Li+, 16O+, 12C+ and 14N+ at the double electrostatic ion-beam storage ring DESIREE. By overlapping two keV ion beams, with corresponding speeds of ca. 1000 km/s, and matching their velocities with applied electric fields, the center-of-mass collision energies are reduced to a few tens of meV. Time- and position-sensitive detectors allow the measurement of the separation of the two formed neutral products, which depends on the kinetic-energy release in the charge-transfer reaction. The branching fractions into the different quantum states are extracted by binning or modelling of the measured product-separation distributions. Due to the difficulty of merged-beams experiments with high mass ratio between the ions, 1H- is often replaced with 2H-. We were able to merge beams with a mass ratio of up to 16 between the ions, which allowed us to use 1H- in all studies presented here. For H-+7Li+ and H-+16O+, we included both hydrogen isotopes, and found a significant isotope effect. The lighter hydrogen isotope leads to an increased population in lower excited states in both cases. Our data constitute important benchmarks for theoretical calculations that are needed in the modelling of stellar photospheres.We compare our experimental findings to different theoretical models and discuss their strengths and shortcomings. In order to achieve these scientific results, the thesis work involved the development of data preparation and analysis for a frame- and an event-based detector, as well as the development of experimental methods.

Electrons that break free during photoionization acquire a phase shift induced by the many-body potential of the parent ion. This phase shift can be interpreted as a delay in the photoionization process. This delay is very brief—on the order of attoseconds—and the time-scale of the process is short enough to, until recently, have been approximated as instantaneous. Recent developments in experimental methods have enabled the generation of light pulses of attosecond duration, allowing these phenomena to be probed in experiments. The photoionization delay can be measured in short-pulse pump-probe experiments that utilizes methods like RABBIT or streaking. Originally these experimental protocols used linearly polarized light and non-angularly resolved measurements. When the capability to use circularly polarized pulses in experiments grow, the numerical methods used to simulate such experiments must follow, and be made capable of accounting for pulses with non-linear polarization. As more experiments collect angularly resolved data it is important to develop tools to analyse these more complex results. This thesis summarizes the work I have done to extend two numerical simulation methods to circular polarization, as well as the extension of a theoretical tool to angularly resolved delays. By decoupling the angular and radial parts through the implementation of coupled two-photon operators, I have enabled the calculation of two-photon matrix elements for any detection angle and combination of photon polarizations. I have computed general formulas for so-called asymmetry parameters that can be used to effectively describe and analyze the angular dependence of cross sections and delays. I have further worked on extending a program suite that simulates the interaction of atoms with light in the time-dependent regime so that it can simulate light of arbitrary polarization. Through these efforts we have found ways to either simplify experiments, or to make them directly sens

The development of high-brilliance X-ray sources, such as the fourth-generation diffraction-limited storage rings and X-ray free-electron lasers, have opened up new possibilities for X-ray imaging and pushed the temporal resolutions of imaging techniques to unprecedented levels. Capturing fast dynamics in two-dimensional (2D), three-dimensional (3D), and even four-dimensional (4D, 3D + time) beyond microsecond temporal resolution has become possible. To fully exploit the unique capabilities of these facilities, challenges such as the data problem must be addressed. Automated tools are needed to handle the large amount of data acquired from each experiment.As a data-driven approach, deep learning has undergone rapid development over the past decade and offers a promising solution to this problem. However, state-of-the-art deep learning methods applied to X-ray imaging ignore the physics of X-ray propagation and interaction with matter and require paired training datasets. In this thesis, we show that combining the physical principles of X-ray imaging with deep learning greatly improves the performance and robustness of the approaches, and it is possible to construct reliable unsupervised approaches, where no paired datasets are needed.Firstly, we present a theoretical background on X-ray imaging and various imaging methods. Secondly, we provide an overview of deep learning, including training strategies and common frameworks for addressing imaging tasks. Lastly, we introduce novel algorithms developed during this thesis:1. FFCGAN, a supervised approach for shot-to-shot flat-field correction at X-ray free-electron lasers.2. PhaseGAN, a phase-retrieval approach for unpaired datasets.3. ONIX, a self-supervised approach for 3D reconstruction from sparse views.4. 4D-ONIX, a self-supervised approach for reconstructing 3D movies from sparse projections.These approaches offer high-quality image reconstructions for X-ray imaging techniques, enabling further exploration and un

Currently, there is a high interest in novel plasmonic platforms and materials able to extend their applicability into the ultraviolet (UV) region of the electromagnetic spectrum. In the UV it is possible to explore the spectral properties of biomolecules that have only a small cross-section in the visible spectral range. However, most plasmonic metals have their resonances at wavelengths >350 nm. Aluminum and rhodium are two exceptions and therefore interesting candidate materials for UV plasmonics. In this work we developed a simple and low-cost preparation of functional substrates based on nanoporous aluminum decorated with rhodium nanoparticles. We demonstrate that these functionalized nanoporous metal films can be exploited as plasmonic materials for enhanced UV Raman spectroscopy.

Based on a recent experimental determination of the static polarizability and a first-principle calculation of the frequency-dependent dipole polarizability of argon, this work presents, by using a Fabry–Perot refractometer operated at 1550 nm, a realization of the SI unit of pressure, the pascal, for pressures up to 100 kPa, with an uncertainty of [(1.0 mPa)2 + (5.8 × 10−6 P)2 + (26 × 10−12P2)2]1/2. The work also presents a value of the molar polarizability of N2 at 1550 nm and 302.9146 K of 4.396572(26) × 10−6 m3/mol, which agrees well with previously determined ones.

This work models and experimentally assesses the influence of absorption of laser light in mirrors in Fabry-Pérot based refractometers used for realization of pressure. Model parameters are assessed by experimental characterizations. Characterizations of two refractometers agree well with the predictions of the model. It is shown that, when pressures are assessed in the viscous region, the absorption of laser light in mirrors will give rise to a small alteration in the proportional response and a pressure-independent offset, where the latter is significant for He but considerably smaller for Ar and N2.

Multilayered metal-dielectric nanostructures display both a strong plasmonic behavior and hyperbolic optical dispersion. The latter is responsible for the appearance of two separated radiative and nonradiative channels in the extinction spectrum of these structures. This unique property can open plenty of opportunities toward the development of multifunctional systems that simultaneously can behave as optimal scatterers and absorbers at different wavelengths, an important feature to achieve multiscale control of light-matter interactions in different spectral regions for different types of applications, such as optical computing or detection of thermal radiation. Nevertheless, the temperature dependence of the optical properties of these multilayered systems has never been investigated. In this work, we study how radiative and nonradiative processes in hyperbolic meta-antennas can probe temperature changes of the surrounding medium. We show that, while radiative processes are essentially not affected by a change in the external temperature, the nonradiative ones are strongly affected by a temperature variation. By combining experiments and temperature-dependent effective medium theory, we find that this behavior is connected to enhanced damping effects due to electron-phonon scattering. Contrary to standard plasmonic systems, a red-shift of the nonradiative mode occurs for small variations of the environment temperature. Our study shows that, to probe temperature changes, it is essential to exploit nonradiative processes in systems supporting plasmonic excitations, which can be used as very sensitive thermometers via linear absorption spectroscopy.

Direct observation of exoplanets and proto-planetary disks with the METIS instrument at the Extremely Large Telescope will provide new insights into the processes of planet formation and exoplanet atmospheres. This will be possible thanks to a powerful vector vortex coronagraph that can suppress the starlight to reveal faint signals around it. Here we present the process of making the phase masks at the heart of the coronagraph. These annular groove phase masks consist of deep sub-wavelength gratings in diamond that are etched using inductively coupled oxygen plasma with a strong bias. The METIS instrument requires a wider bandwidth than such components have previously been demonstrated for, leading to a grating design with higher aspect ratio and more vertical walls. To achieve this, the etch mask used for diamond etching was changed from aluminium to silicon and the plasma power was increased. We also improved on our method for reducing the grating depth of finished components to fine-tune them. Together with improved optical testing, this allowed us to produce the best vortex phase masks so far demonstrated for the astronomical N-band.

This thesis project explores period doubling in optical frequency combs, an area with limited prior research. An optical frequency comb can be used in telecommunications and high-precision metrologyand is a coherent set of discrete, equidistant frequency components generated from a central pumplaser frequency. To simulate the combs and the evolution of the intracavity field, the Ikeda map and two coupled mean-field equations for the period doubling regime are employed. The equations ofthese mathematical models are first derived, followed by an analytical investigation of the modulationinstability in the period doubling regime. Furthermore, the period doubling regime is simulated numerically to investigate stability and the generation of various comb patterns. During the simulations, the initial pump power is held constant while the detuning is varied. It is found that the energy was highest where the eigenvalue had the biggest real part from the analytical investigation. Additionalinstabilities is shown in results from simulations with normal dispersion.

Assessing the mixing of two liquids is a critical task in the biotechnical industry. At Cytiva, affinity chromatography columns depend on a well-mixed aqueous salt solution to release the target from the affinity resin. A mixer is often incorporated into the flow path to ensure effective mixing of the liquids.These mixers generate complex three-dimensional flowfields, and existing measurement techniques frequently average the flow depth, thereby losing essential spatial information. This project introduces and implements a novel method for assessing mixing in four dimensions, requiring simultaneous imaging of the flow from multiple view points. The flowfield is reconstructed from the image data using a least squares tomographic reconstruction technique. Additionally, a methodwas developed to reconstruct the same flowfield numerous times using different underlying section meshes. These results are then interpolated on a common grid and averaged. The findings demonstrate that this method accurately resolves the flowfield qualitatively and quantitatively. The averaging method enables lower downsampling factors and higher overall accuracy. However, challenges such as achieving uniform pipe illumination and enhancing data acquisition rates remain. Addressing these issues is essential for fully resolving three-dimensional flowfields over time. Future work will improve lighting and data acquisition to enhance the method’s applicability for higher Reynolds number applications.

The aim of the project was to understand and provide a simple template for building programmable, universal multiport interferometer (a linear optics setup) given an initial unitary matrix. Starting with an N × N unitary matrix Û of finite dimension, how do we construct a linear optics setup that performs the operation on the state of photons? An answer can be found with a decomposition algorithm. First, we define the mathematical description of the photons. Second, we build up our understanding of the decomposition. Third, we explore the mathematics of the decomposition and provide proofs for some critical properties. Fourth, we briefly explain the steps one might take in order to fabricate the setup. The decomposition consists of separating the unitary matrix into a product of simpler factors using Clements et al.’s algorithm. Each factor represents one component of the setup. The final multiport interferometer is a rectangle mesh consisting of variable phase shifters and 50/50 beam splitters, which can be interpreted as Mach-Zehnder interferometers in a zig-zag-like pattern. The next steps would be to fabricate and test the interferometer. We encode the information in photon path, which can be implemented on various platforms (for example, photonic integrated circuits). However, the mathematics is applicable to all systems with interference-like behaviour.