Soft Pulses Research Articles

Single-shot arrival timing diagnostics for a soft X-ray free-electron laser beamline at SACLA.

Arrival timing diagnostics performed at a soft X-ray free-electron laser (FEL) beamline of SACLA are described. Intense soft X-ray FEL pulses with one-dimensional focusing efficiently induce transient changes of optical reflectivity on the surface of GaAs. The arrival timing between soft X-ray FEL and optical laser pulses was successfully measured as a spatial position of the reflectivity change. The temporal resolution evaluated from the imaging system reaches ∼10 fs. This method requires only a small portion of the incident pulse energy, which enables the simultaneous operation of the arrival timing diagnostics and experiments by introducing a wavefront-splitting scheme.

Theoretical investigation of atomic low-order harmonics under irradiation of two high frequency laser pulses

With the development of laser technology,the extreme ultraviolet and X-ray light sources can be obtained by utilizing the high-order harmonic radiation and the free electron laser.When an atom is irradiated by an intense highfrequency laser,many nonlinear phenomena can be observed,such as high-order harmonic emission,threshold ionization and ionization stability of atom,etc. The emission spectra with some new features appear when the atom is irradiated by a high-frequency laser pulse. The harmonic spectra with a clear cut-off plateau do not appear,and the three-step model is no longer valid for explaining the results.In addition to the odd-order harmonic radiation observed in the emission spectra,many super-Raman lines can be seen clearly.These radiations are generated from the transition between the dressed eigenstates of the atom. When the incident high-frequency laser pulse is strong enough,the peak of the harmonic splits into many sub-peaks. The generation of the sub-peaks of harmonic is due to the contributions from the rising and falling parts in the pulse. With the development of free electron laser technology,one can obtain a combined pulse with different frequencies. Many new two-color schemes are proposed for the experiment,such as the realization of two-photon spectrometer, pump-probe spectrometer.In this work,we investigate the optical radiation of the atom irradiated by a combined laser pulse,whose energies are higher than the ionization energy of the atom.It is found that the odd harmonics of the two high frequencies are shown in the emission spectra,and many satellite peaks appear in the vicinity of these odd harmonics.Furthermore,the intensities of the satellite peaks are enhanced exponentially with the increase of the incident laser intensity,and the frequency difference between the two adjacent peaks is the frequency difference between the two incident laser pulses.We study the time-frequency profile of the harmonic emission by analyzing the wavelets.With the two-color scheme one can achieve coherent soft X-ray and produce short coherent pulse. We also calculate the high-order harmonic spectrum of hydrogen in the two-color laser pulse,the multi-peak structure in the emission spectra can also be found,and the positions and intensity distribution of the emission peaks are consistent well with those from the one-dimensional calculation.In our two-color scheme,by changing the peak intensity and frequency of one of the combined laser pulses,the multi-plateau structure can be shown in the harmonic spectra.Taking advantage of the harmonic plateau,the soft X-ray radiation and ultra-short attosecond pulse chain can be generated.

Optimizing Seat Belt and Airbag Designs for Rear Seat Occupant Protection in Frontal Crashes.

Recent field data have shown that the occupant protection in vehicle rear seats failed to keep pace with advances in the front seats likely due to the lack of advanced safety technologies. The objective of this study was to optimize advanced restraint systems for protecting rear seat occupants with a range of body sizes under different frontal crash pulses. Three series of sled tests (baseline tests, advanced restraint trial tests, and final tests), MADYMO model validations against a subset of the sled tests, and design optimizations using the validated models were conducted to investigate rear seat occupant protection with 4 Anthropomorphic Test Devices (ATDs) and 2 crash pulses. The sled tests and computer simulations were conducted with a variety of restraint systems including the baseline rear-seat 3-point belt, 3-point belts with a pre-tensioner, load limiter, dynamic locking tongue, 4-point belts, inflatable belts, Bag in Roof (BiR) concept, and Self Conforming Rear seat Air Bag (SCaRAB) concept. The results of the first two sled series demonstrated that the baseline 3-point belt system are associated with many injury measures exceeding injury assessment reference values (IARVs); showed the significance of crash pulse and occupant size in predicting injury risks; and verified the potential need of advanced restraint features for better protecting the rear-seat occupants. Good correlations between the tests and simulations were achieved through a combination of optimization and manual fine-tuning, as determined by a correlation method. Parametric simulations showed that optimized belt-only designs (3-point belt with pre-tensioner and load limiter) met all of the IARVs under the soft crash pulse but not the severe crash pulse, while the optimized belt and SCaRAB design met all the IARVs under both the soft and severe crash pulses. Two physical prototype restraint systems, namely an "advanced-belt only" design and an "advanced-belt and SCaRAB" design, were then tested in the final sled series. With the soft crash pulse, both advanced restraint systems were able to reduce all the injury measures below the IARVs for all four ATDs. Both advanced restraint systems also effectively reduced almost all the injury measures for all ATDs under the severe crash pulse, except for the THOR. The design with the advanced-belt and SCaRAB generally provided lower injury measures than those using the advanced belt-only design. This study highlighted the potential benefit of using advanced seatbelt and airbag systems for rear-seat occupant protection in frontal crashes.

Formula omitted] gradient coherence selection using a tapered stripline

Pulsed-field gradients are common in modern liquid state NMR pulse sequences. They are often used instead of phase cycles for the selection of coherence pathways, thereby decreasing the time required for the NMR experiment. Soft off-resonance pulses with a B1 gradient result in a spatial encoding similar to that created by pulsed-field (B0) gradients. In this manuscript we show that pulse sequences with pulsed-field gradients can easily be converted to one which uses off-resonance B1 field gradient (OFFBEAT) pulses. The advantage of B1 gradient pulses for coherence selection is that the chemical shift evolution during the pulses is (partially) suppressed. Therefore no refocusing echos are required to correct for evolution during the gradient pulses. A tapered stripline is shown to be a convenient tool for creating a well-defined gradient in the B1 field strength. B1 gradient coherence selection using a tapered stripline is a simple and cheap alternative to B0 pulsed-field gradients.

A Storage Ring Based Free-Electron Laser for Generating Ultrashort Coherent EUV and X-ray Radiation

Generation of ultrashort coherent radiation pulses in the extreme ultraviolet (EUV) and x-ray regime is of remarkable interest in the synchrotron radiation user community. In this work, a novel technique is proposed for directly imprinting strong coherent microbunching on the electron beam with very small laser-induced energy spread. Theoretical analysis and numerical simulations demonstrated that this technique can be used for the generation of megawatt-scale level, fully temporal coherent femtosecond EUV and soft x-ray radiation pulses at a storage ring light source.

Angular streaking and sideband formation in rotating terahertz and far-infrared fields

Electron spectra in atomic ionization by extreme ultraviolet (XUV) or soft x-ray femtosecond pulses, in the presence of a strong circularly polarized far-infrared or terahertz (THz) field are theoretically investigated. When the XUV pulse duration is much shorter than the period of the THz field, the conditions for circular streaking are fulfilled. The peculiarities of the circular streaking are discussed. In the other extreme case when the duration of the XUV pulse is longer than the THz field period, an analog of the sidebands is formed. Special attention is paid to the intermediate case when the duration of the XUV pulse is similar to the THz period. In this case, a well-developed interference structure appears in the photoelectron spectra. A quasiclassical description of this interference structure is presented and compared with numerical calculations based on a quantum-mechanical approach.

Аттосекундные нанотехнологии: электронные механизмы формирования неравновесных квантовых супра-атомных наноструктур материалов

A theory of one- and two-electron nonequilibrium phenomena on time-spatial levels of quantum supra-atomic nanostructures in materials caused by deep-UV and soft X-ray attosecond pulses is well developed within the fundamental concept of thermal field dynamics. It is shown that time-base sweep of nonequilibrium processes of supra-atomic level formation caused by attosecond pulses starts with the local birth of coherent-entangled static x-gauge modes of two-electron fluctuation electromagnetic fields. The two-electron fluctuation energy accumulates as a quantum electromechanical energy of static x-gauge modes. It results in spontaneous appearance of static electromagnetic loggie 0.1-10 nm in size that include electron pairs and x-gauge modes. Boundaries of the static electromagnetic loggie have kink topological singularities of x-gauge modes in physical space. Finite loggie of coherent-entangled electron pairs enclose Fermi gas of electrons and nuclei and set a topological matrix of quantum electromechanical interfaces in a material. The quantum topology of loggie spatial carriers is a cover of a quantum topology of atoms and single-electron Fermi gas of condensed state.

Ways of development of compact coherent femtosecond X-ray sources for applications in nano- and biophotonics

Ways of the development of compact coherent sources of soft X-ray femtosecond pulses are discussed, which meet the requirements for the implementation of the “diffraction-before-destruction” approach in the lensless X-ray Coherent Diffractive Imaging (CDI) technique enabling quantitative 3D mapping of material structure with the nanoscale spatial resolution. An innovative hybrid (solid/gas) approach to produce ultra-intense femtosecond laser pulses in the visible is described in the context of its applications for laser driven high harmonic generation (HHG) and soft X-ray generation in laser plasmas due to recombination mechanism of excitation.

Quadrupolar solid-state NMR and repetitive experiments: Some aspects in the Liouville space. Application to spins I=1

The aim of this work is to generalize the Ernst-Anderson model developed to account of the steady-state regime of isolated spins I=1/2 subject to a train of strictly identical pulse sequences separated by free evolution periods of same duration. We generalize this model to the general case of spins I≥1 and general pulse sequence within the framework of the Liouville space. In particular, it is proved that under reasonable assumptions, a well defined steady-state regime is reached which is independent of the initial conditions. The general formal expressions obeyed by the steady-state density operator are given as a function of pulse propagators and relaxation operator for single and two-pulse sequences. In solid-state NMR where recycle time can be made, at the same time, much longer than typical coherence relaxation times and smaller than typical population relaxation times, further simplification leads to more tractable formula. As an example, the formalism is applied to I=1 spins with hard and soft single pulse sequence, or to the solid echo sequence. In particular, we were able to generalize the Ernst-Anderson formula to spins I=1. The pertinence of the theory is verified by comparing the theoretical and numerical simulations outputs to 2H single crystal experiments performed on nonadecane/urea C19D40/urea−H4 compound.

Selective excitation for spectral editing and assignment in separated local field experiments of oriented membrane proteins

Spectroscopic assignment of NMR spectra for oriented uniformly labeled membrane proteins embedded in their native-like bilayer environment is essential for their structure determination. However, sequence-specific assignment in oriented-sample (OS) NMR is often complicated by insufficient resolution and spectral crowding. Therefore, the assignment process is usually done by a laborious and expensive “shotgun” method involving multiple selective labeling of amino acid residues. Presented here is a strategy to overcome poor spectral resolution in crowded regions of 2D spectra by selecting resolved “seed” residues via soft Gaussian pulses inserted into spin-exchange separated local-field experiments. The Gaussian pulse places the selected polarization along the z-axis while dephasing the other signals before the evolution of the 1H-15N dipolar couplings. The transfer of magnetization is accomplished via mismatched Hartmann-Hahn conditions to the nearest-neighbor peaks via the proton bath. By optimizing the length and amplitude of the Gaussian pulse, one can also achieve a phase inversion of the closest peaks, thus providing an additional phase contrast. From the superposition of the selective spin-exchanged SAMPI4 onto the fully excited SAMPI4 spectrum, the 15N sites that are directly adjacent to the selectively excited residues can be easily identified, thereby providing a straightforward method for initiating the assignment process in oriented membrane proteins.

Dietary intake in people consuming a reduced-carbohydrate diet in the National Diet and Nutrition Survey.

Diets reduced or low in carbohydrates are becoming increasingly popular. The replacement foods and their accompanying nutrients determine the health effects of such diets. However, little is known about the dietary intake of people consuming reduced or low carbohydrate diets. In this cross-sectional study, the dietary and nutrient intake of individuals aged 16-75 years consuming less than 40% of energy from carbohydrate (n = 430) was compared with individuals consuming equal to or more than 40% energy from carbohydrate (n = 1833) using the UK National Diet and Nutrition Survey. Those consuming less than 40% of total energy from carbohydrate reported a higher consumption of red and processed meat, butter, oily fish and vegetables, as well as a lower consumption of soft drinks and pulses, than those with a normal carbohydrate intake. After adjusting for socio-economic status, only red meat intake was different between the groups, and reached the maximum recommended daily intake daily intake. There were no significant differences in micronutrient intakes between the groups, although magnesium, selenium and potassium, along with fibre, were lower than recommended amounts across the cohort. Individuals consuming reduced or low carbohydrate diets could benefit from replacing some red meats with white meats and vegetable sources of protein, and increasing vegetable intake.

Selective-pulse-network compilation on a liquid-state nuclear-magnetic-resonance system

In creating a large-scale quantum information processor, the ability to construct control pulses for implementing an arbitrary quantum circuit in a scalable manner is an important requirement. For liquid-state nuclear magnetic resonance (NMR) quantum computing, a circuit is generally realized through a sequence of selective soft pulses, in which various control imperfections exist and are to be corrected. In this work, we present a comprehensive analysis of the errors arisen in a selective pulse network by using the zeroth and first order average Hamiltonian theory. Effective correction rules are derived for adjusting important pulse parameters such as irradiation frequencies, rotational angles and transmission phases of the selective pulses to increase the control fidelity. Simulations show that applying our compilation procedure for a given circuit is efficient and can greatly reduce the error accumulation.

Experimental realization of robust dynamical decoupling with bounded controls in a solid-state spin system

We experimentally demonstrate a robust dynamical decoupling protocol with bounded controls using long soft pulses, eliminating a challenging requirement of strong control pulses in conventional implementations. This protocol is accomplished by designing the decoupling propagators to go through a Eulerian cycle of the coupler group [Phys. Rev. Lett. 90, 037901(2003)]. We demonstrate that this Eulerian decoupling scheme increases the coherence time by two orders of magnitude in our experiment under either dephasing or a universal noise environment.

A single stage EEHG at SXFEL for narrow-bandwidth soft X-ray generation

The echo-enabled harmonic generation (EEHG) scheme holds promising prospects for efficiently generating intense coherent radiation at very high harmonics of the initial seed laser. In this paper, we study the feasibility of operating the Shanghai X-ray free-electron laser test facility with a single stage EEHG setup. With a combination of existing numerical codes, start-to-end simulations considering various three-dimensional effects have been carried out to show the possible performance of the EEHG FEL. Simulation results demonstrate that a single stage EEHG can generate high power soft X-ray radiation pulses with narrow bandwidth directly from UV seed lasers. With the help of the harmonic lasing technique or upgraded linac, we also show the possibility of generating coherent soft X-ray radiation in the “water window” with a single stage EEHG.

Fokker-Planck formalism in magnetic resonance simulations

This paper presents an overview of the Fokker-Planck formalism for non-biological magnetic resonance simulations, describes its existing applications and proposes some novel ones. The most attractive feature of Fokker-Planck theory compared to the commonly used Liouville - von Neumann equation is that, for all relevant types of spatial dynamics (spinning, diffusion, stationary flow, etc.), the corresponding Fokker-Planck Hamiltonian is time-independent. Many difficult NMR, EPR and MRI simulation problems (multiple rotation NMR, ultrafast NMR, gradient-based zero-quantum filters, diffusion and flow NMR, off-resonance soft microwave pulses in EPR, spin-spin coupling effects in MRI, etc.) are simplified significantly in Fokker-Planck space. The paper also summarises the author’s experiences with writing and using the corresponding modules of the Spinach library – the methods described below have enabled a large variety of simulations previously considered too complicated for routine practical use.

Effect of the rate of rise in discharge current on the output of a 46.9-nm soft X-ray laser based on capillary discharge

The rate of rise in discharge current (dI/dt) is an important parameter in an X-ray laser pumped by fast capillary discharge. The effect of this parameter on the energy of an argon plasma-based 46.9-nm soft X-ray laser pulse has been experimentally studied. It was found that an X-ray laser pulse with ~2 μJ energy, which can be obtained at a discharge current of ~40 kA with dI/dt value of ~7.1 × 1011 A/s, can also be obtained at a much lower peak current of ~26 kA if the quarter period (T/4) of the discharge current is made shorter to achieve a comparable dI/dt value. For a fixed T/4, the laser energy could be enhanced from 2 to 4 μJ for an increase in the dI/dt value from 7.1 × 1011 to 1.3 × 1012 A/s by increasing the peak current from 26 to 44 kA. It was also observed that for a fixed dI/dt, mere increase in the discharge current does not increase the laser energy.

Universal set of dynamically protected gates for bipartite qubit networks: Soft pulse implementation of the [[5,1,3]] quantum error-correcting code

We model repetitive quantum error correction (QEC) with the single-error-correcting five-qubit code on a network of individually controlled qubits with always-on Ising couplings. We use our previously designed universal set of quantum gates based on sequences of shaped decoupling pulses. In addition to being accurate quantum gates, the sequences also provide dynamical decoupling (DD) of low-frequency phase noise. The simulation involves integrating the unitary dynamics of six qubits over the duration of tens of thousands of control pulses, using classical stochastic phase noise as a source of decoherence. The combined DD and QEC protocol dramatically improves the coherence, with the QEC alone being responsible for more than an order of magnitude infidelity reduction.

Time-resolved x-ray imaging of a laser-induced nanoplasma and its neutral residuals

The evolution of individual, large gas-phase xenon clusters, turned into a nanoplasma by a high power infrared laser pulse, is tracked from femtoseconds up to nanoseconds after laser excitation via coherent diffractive imaging, using ultra-short soft x-ray free electron laser pulses. A decline of scattering signal at high detection angles with increasing time delay indicates a softening of the cluster surface. Here we demonstrate, for the first time a representative speckle pattern of a new stage of cluster expansion for xenon clusters after a nanosecond irradiation. The analysis of the measured average speckle size and the envelope of the intensity distribution reveals a mean cluster size and length scale of internal density fluctuations. The measured diffraction patterns were reproduced by scattering simulations which assumed that the cluster expands with pronounced internal density fluctuations hundreds of picoseconds after excitation.

Photoacoustic monitoring of chorioretinal complex during laser coagulation of ocular fundus

The effect of laser treatment on ocular fundus tissues depends on quite a number of factors, mostly uncontrollable, hence, laser output parameters may vary dramatically even within the same fundus. In classical procedure ('threshold' laser coagulation), these parameters are adjusted to ophthalmoscopically visible tissue color changes at the site of coagulation. However, this method does not work with modern subthreshold techniques, that are more tissue-saving and thus, produce no immediate and visible changes in the retina. Calculation methods that are used instead are much less accurate. Photoacoustic monitoring may become a real breakthrough in this field. The method involves acoustic analysis of the response to soft and short laser pulses ('test' pulses). Heating of the target by the main therapeutic laser causes alterations in its physical properties and, consequently, the laser-induced acoustic signal. This gives us an ability to monitor the temperature and thus, to evaluate the clinical effect of coagulation despite the absence of visible changes at the site. The most promising techniques of photoacoustic monitoring that are being developed are discussed here.

Comparative Tissue Proteomics of Microdissected Specimens Reveals Novel Candidate Biomarkers of Bladder Cancer

More than 380,000 new cases of bladder cancer are diagnosed worldwide, accounting for ∼150,200 deaths each year. To discover potential biomarkers of bladder cancer, we employed a strategy combining laser microdissection, isobaric tags for relative and absolute quantitation labeling, and liquid chromatography-tandem MS (LC-MS/MS) analysis to profile proteomic changes in fresh-frozen bladder tumor specimens. Cellular proteins from four pairs of surgically resected primary bladder cancer tumor and adjacent nontumorous tissue were extracted for use in two batches of isobaric tags for relative and absolute quantitation experiments, which identified a total of 3220 proteins. A DAVID (database for annotation, visualization and integrated discovery) analysis of dysregulated proteins revealed that the three top-ranking biological processes were extracellular matrix organization, extracellular structure organization, and oxidation-reduction. Biological processes including response to organic substances, response to metal ions, and response to inorganic substances were highlighted by up-expressed proteins in bladder cancer. Seven differentially expressed proteins were selected as potential bladder cancer biomarkers for further verification. Immunohistochemical analyses showed significantly elevated levels of three proteins-SLC3A2, STMN1, and TAGLN2-in tumor cells compared with noncancerous bladder epithelial cells, and suggested that TAGLN2 could be a useful tumor tissue marker for diagnosis (AUC = 0.999) and evaluating lymph node metastasis in bladder cancer patients. ELISA results revealed significantly increased urinary levels of both STMN1 and TAGLN2 in bladder cancer subgroups compared with control groups. In comparisons with age-matched hernia urine specimens, urinary TAGLN2 in bladder cancer samples showed the largest fold change (7.13-fold), with an area-under-the-curve value of 0.70 (p < 0.001, n = 205). Overall, TAGLN2 showed the most significant overexpression in individual bladder cancer tissues and urine specimens, and thus represents a potential biomarker for noninvasive screening for bladder cancer. Our findings highlight the value of bladder tissue proteome in providing valuable information for future validation studies of potential biomarkers in urothelial carcinoma.