Source Of Soft X-ray Radiation Research Articles

Robust Isolated Attosecond Pulse Generation with Self-Compressed Subcycle Drivers from Hollow Capillary Fibers.

High-order harmonic generation (HHG) arising from the nonperturbative interaction of intense light fields with matter constitutes a well-established tabletop source of coherent extreme-ultraviolet and soft X-ray radiation, which is typically emitted as attosecond pulse trains. However, ultrafast applications increasingly demand isolated attosecond pulses (IAPs), which offer great promise for advancing precision control of electron dynamics. Yet, the direct generation of IAPs typically requires the synthesis of near-single-cycle intense driving fields, which is technologically challenging. In this work, we theoretically demonstrate a novel scheme for the straightforward and compact generation of IAPs from multicycle infrared drivers using hollow capillary fibers (HCFs). Starting from a standard, intense multicycle infrared pulse, a light transient is generated by extreme soliton self-compression in a HCF with decreasing pressure and is subsequently used to drive HHG in a gas target. Owing to the subcycle confinement of the HHG process, high-contrast IAPs are continuously emitted almost independently of the carrier-envelope phase (CEP) of the optimally self-compressed drivers. This results in a CEP-robust scheme which is also stable under macroscopic propagation of the high harmonics in a gas target. Our results open the way to a new generation of integrated all-fiber IAP sources, overcoming the efficiency limitations of usual gating techniques for multicycle drivers.

Spatial and temporal evolution of laser plasma produced using a double-stream gas puff target

Laser plasma produced using a double-stream gas puff target is an intense source of soft x-ray (SXR) and extreme ultraviolet (EUV) radiation, however, without the harmful emission of debris associated with a solid target. Debris-free laser plasma x-ray and EUV sources have been applied in many various applications, including metrology, imaging in a nanoscale, tomography, processing materials, emission and absorption spectroscopy, laboratory astrophysics and astrochemistry, radiobiology, and radiochemistry. In this work, the results of the experimental and theoretical studies on the spatial and temporal evolution of laser plasma produced as a result of irradiation of an argon/helium gas puff target with laser pulses of 1.3 or 6 ns time duration generated with an Nd:YAG laser system are presented. Imaging and spectral measurements of SXR emission from the plasma, created in the double-stream gas puff target, have been performed with the use of an x-ray streak camera. The analysis of the results of spectral measurements, supported by numerical simulations of plasma x-ray emission, allowed the estimation of the plasma electron temperature and its changes over time. Experimental data were compared with the results of theoretical studies performed using a computer model of plasma hydrodynamics. It was shown that plasma expansion is fast enough to reduce the plasma density in the laser focus area during the laser–plasma interaction.

Fast capillary discharge device for soft x-ray generation in the “carbon-window” and “water-window” spectral regions

The paper presents a compact source of soft X-ray radiation based on a fast capillary discharge developed for “water window” microscopy methods. The central part of the source is the specially designed nanosecond voltage pulse generator capable of operating at a frequency of 600 Hz, with 100 ns pulse duration and energy per pulse 5 J. The discharge is created in a borosilicate capillary non-uniformly filled with gas. The plasma emission spectra obtained for the case of source operation in argon-helium mixture demonstrate well-pronounced lines in the “carbon window” range, in carbon dioxide-lines in the “water window” range. An analysis of the emission spectra in the range of 2–9 nm in cases of different inlet gas pressures made it possible to estimate the degree of ablation of the inner wall of the capillary and to determine the suitable operating pressure range.

Broadband impedance modeling and single bunch instabilities estimations of the advanced light source upgrade project

The Advanced Light Source Upgrade (ALS-U) is a 4th generation diffraction-limited soft x-ray radiation source, consisting of a new accumulator ring (AR) and a new storage ring (SR). In both rings coupling-impedance driven instabilities need careful evaluation to ensure meeting the machine’s high-performance goals. This paper presents the workflow followed in building the impedance models and the beam-stability analysis based on those models. We follow the commonly accepted approach of separating the resistive-wall and the geometric parts of the impedance; the former is obtained by analytical formulas, the latter by numerical electro-magnetic codes (primarily CST Studio software) with perfectly-conducting boundary conditions.Impedance budgets are established and pseudo-Green functions calculated to be used in beam dynamics studies. We also present various ways to cross-check simulation results for reliable impedance modeling. Finally, the crucial single-bunch instability current thresholds for various operation modes are determined and discussed.

Оптимизация параметров компактного источника мягкого рентгеновского излучения для работы в диапазоне длин волн 2-5 nm

This paper presents a compact source of soft X-ray radiation for operation in the wavelength range of 2-5 nm with a pulse repetition frequency of more than 500 Hz. The source parameters were optimized to reduce the intensity of ablation of the discharge volume wall and obtain the maximum intensity of the spectral lines of multicharged ions C V – 4 nm and Ar IX – 4.87 nm. The obtained results can be used in the development of a microscope for the tasks of cell lumen microscopy with nanometer resolution.

Optimization of parameters of a compact soft X-ray source for operation in the wavelength range 2-5 nm

This paper presents a compact source of soft X-ray radiation for operation in the wavelength range of 2-5 nm with a pulse repetition frequency of more than 500 Hz. The source parameters were optimized to reduce the intensity of ablation of the discharge volume wall and obtain the maximum intensity of the spectral lines of multicharged ions C V --- 4 nm and Ar IX --- 4.87 nm. The obtained results can be used in the development of a microscope for the tasks of cell transmission microscopy with nanometer resolution. Keywords: High-voltage pulse generator, Capillary plasma, "Water-window" microscopy.

Measurements of the absolute values of the radiation intensity in the wavelength range of 6.6-32 nm of stainless steel targets with pulsed laser excitation

The paper presents experimental data on the absolute values of the radiation intensity in the wavelength range of 6.6-32 nm for a stainless steel target excited by a Nd: YAG laser with parameters λ=1064 nm, Epulse=0.45 J, tau=4 ns, ν=10 Hz. The results are of interest for various applications using laboratory laser-plasma sources of soft X-ray and extreme ultraviolet radiation. Keywords: extreme ultraviolet radiation, emission spectrum, laser spark, multilayer X-ray mirror.

Theoretical study of soft X-ray emission and dynamics of laser-induced plasma of double stream gas puff

The double stream gas puff-based laser-produced plasma is studied as a source of soft X-ray radiation in nm wavelength spectral range. Dynamics of plasma induced by Nd:YAG laser beam and its emission is simulated with radiation-magnetohydrodynamic code Zstar. The modeling results for krypton gas stream in an annular helium jet as a circumferential gas for various picosecond and nanosecond laser pulses corresponding to the experiments are presented. The spatial–spectral features and temporal behavior of the soft X-ray and EUV emission are investigated. Under ps pulse, the gas is rapidly ionized in the laser beam channel, but it does not have enough time to shift sensibly during the pulse, and the plasma electron density grows against the background of almost constant ion density during the ionization in the laser radiation field. There is ionization instability only capable to be developed in ps range. At ns pulse, the gas ionization and heating leads to gas pushing out of the channel, and the formation of a divergent compression wave transforming into the shock wave. Behind the compression wave front, conditions arise for the development of Rayleigh–Taylor-type instability. The instability leads to the redistribution of plasma temperature and density, and to the formation of increased soft X-ray emission spots. Time evolution of spatial distributions and spectral characteristics of emitted SXR radiation is analyzed for different laser pulses. Transient effects in multicharged ion plasma are discussed, fundamental understanding of those is required for optimization of plasma radiation source. A conversion efficiency of laser energy into soft X-ray wavebands from krypton plasma is scanned by laser parameters and analyzed.

Towards soft x-ray fluorescence measurements in the laboratory using a laser-produced plasma source and a complementary metal-oxide semiconductor detector

With the advent of commercially available CMOS technology suitable for direct detection of photons in the soft X-ray range, new possibilities are opening up for the improvement and optimization of experiments requiring energy discrimination capabilities in this energy range. SDDs are widely used as energy-dispersive detectors, but they cannot be used with pulsed sources due to the overwhelming temporal photon density. Wavelength-dispersive solutions offer unmatched energy resolution, but suffer from low detection efficiency and a limited energy bandwidth which can be monitored. The use of common CCDs as energy-dispersive detectors in this energy range is limited by their energy resolution and especially their readout speed, which can result in significant experimental dead time and limits the usable frequency of pulsed sources. Therewhile, CMOS detectors with high energy resolution and high frame rates are an efficient, versatile and cost-effective alternative as detectors for pulsed sources. In this work we present the characterization of a commercially available, backside-illuminated CMOS detector regarding its energy resolution and quantum efficiency at the BESSY II synchrotron radiation facility with a well-known soft X-ray radiation source. Furthermore it is used in a proof of principle XRF measurement with a laboratory-based laser-plasma source.

Измерения абсолютных значений интенсивности излучения в диапазоне длин волн 6.6-32 nm мишени из нержавеющей стали при импульсном лазерном возбуждении

The paper presents experimental data on the absolute values ​​of the radiation intensity in the wavelength range of 6.6-32 nm for a stainless steel target excited by a Nd: YAG laser with parameters λ = 1064 nm, Еpulse = 0.45 J, τ = 4 ns, ν = 10 Hz. The results are of interest for various applications using laboratory laser-plasma sources of soft X-ray and extreme ultraviolet radiation.

On the Size of the Soft X-Ray Radiation Source Based on an X-Pinch

The advent of X-pinch based compact radiographs has significantly expanded the application field of pulsed radiography for diagnostics of fast processes. The key point here is the spatial resolution which these radiographs can provide. The method for determining the size of the soft x-ray (SXR) source based on diffraction imaging of opaque metallic wires and their comparison with the diffraction pattern calculated for an extended source in a given spectral range is presented in the paper. The X-pinch source sizes have been measured taking into account the sensitometric characteristic of the film and the scanner characteristics. By this method it has been shown that the diameter of the X-pinch radiation source for current rise rates in the range 0.7–1.35 kA/ns varies slightly for the spectral range hv >3 keV.

A Soft X-Ray Radiation Source Formed in Supersonic Argon Gas Jets under the Action of High-Contrast Femtosecond Laser Pulses of Relativistic Intensity

The possibility of designing a compact source of soft X-ray radiation without the accompanying generation of fast electrons is under study. The source is formed by the interaction of high-contrast femtosecond laser pulses of relativistic intensity with supersonic argon gas jets. The optimal conditions are found under which the conversion coefficient to soft X-ray radiation in the range of 2.9–3.3 keV reaches 8.57 × 10–5.

Clean source of soft X-ray radiation formed in supersonic Ar gas jets by high-contrast femtosecond laser pulses of relativistic intensity

In this work, we optimized a clean, versatile, compact source of soft X-ray radiation $(E_{\text{x}\text{-}\text{ray}}\sim 3~\text{keV})$ with an yield per shot up to $7\times 10^{11}~\text{photons}/\text{shot}$ in a plasma generated by the interaction of high-contrast femtosecond laser pulses of relativistic intensity $(I_{\text{las}}\sim 10^{18}{-}10^{19}~\text{W}/\text{cm}^{2})$ with supersonic argon gas jets. Using high-resolution X-ray spectroscopy approaches, the dependence of main characteristics (temperature, density and ionization composition) and the emission efficiency of the X-ray source on laser pulse parameters and properties of the gas medium was studied. The optimal conditions, when the X-ray photon yield reached a maximum value, have been found when the argon plasma has an electron temperature of $T_{\text{e}}\sim 185~\text{eV}$ , an electron density of $N_{\text{e}}\sim 7\times 10^{20}~\text{cm}^{-3}$ and an average charge of $Z\sim 14$ . In such a plasma, a coefficient of conversion to soft X-ray radiation with energies $E_{\text{x}\text{-}\text{ray}}\sim 3.1\;(\pm 0.2)~\text{keV}$ reaches $8.57\times 10^{-5}$ , and no processes leading to the acceleration of electrons to MeV energies occur. It was found that the efficiency of the X-ray emission of this plasma source is mainly determined by the focusing geometry. We confirmed experimentally that the angular distribution of the X-ray radiation is isotropic, and its intensity linearly depends on the energy of the laser pulse, which was varied in the range of 50–280 mJ. We also found that the yield of X-ray photons can be notably increased by, for example, choosing the optimal laser pulse duration and the inlet pressure of the gas jet.

Study of the features of ultrafast silicon-carbide current switch for sources of soft x-ray radiation based on capillary plasma

The results of the development and experimental investigation of high-voltage silicon-carbide high-speed current switches – drift step recovery diodes (DSRD) – and their implementation as a part of soft X-ray source based on capillary plasma are presented.

О размере источника мягкого рентгеновского излучения на основе Х-пинча

О размере источника мягкого рентгеновского излучения на основе Х-пинча

Computation of intensity and polarization state of diffracted fields from reflective gratings in conical geometry.

Conical diffraction geometry has interesting properties for monochromatization of short pulse sources of extreme-UV or soft X-ray radiation, like high harmonic generation in gases. It enables high diffraction efficiency at the cost of a reduced angular dispersion. Computation of grating efficiency is complex when the incidence plane is not perpendicular to the grating lines because S and P polarizations are coupled. We have therefore developed a special code, named COROX, which implements a rigorous coupled-wave analysis algorithm. The code is able to compute the complex diffracted field from any incidence direction and polarization on any kind of grating (thick lamellar and blazed gratings with single or multilayer coating). COROX is developed with C++ and uses an eigen linear algebra library. This paper outlines the method of computation, and the results are given for a 150 l/mm blazed grating in a conical Littrow configuration.

Scaling for ultrashort pulse amplification in plasma via backward Raman amplification scheme operating in the short wavelength regime

The applicability of extreme ultraviolet (XUV) and soft x-ray radiation sources in a resonant backward Raman amplification (BRA) scheme in amplifying the weak ultrashort sub-femtosecond pulses has been examined. Utilizing the slowly-varying-envelope-approximation-based analytical expressions for the resonant three-wave interaction along with viable physics constraint, a parameter space configuring the laser/plasma features required to achieve significant pulse amplification and compression has been derived. A specific parametric configuration for resonant BRA operation in the short wavelength regime has been identified and validated using particle in cell simulation results. The outcome predicts that the resonant BRA scheme may efficiently be applied to amplify the weak pulses for the pump radiation operating within the XUV regime; the effect may be optimized via efficient tuning of the plasma density, pump pulse intensity, and wavelength of the interacting waves. As an illustration, resonant BRA scheme in reference to a DESY FLASH XUV laser source has been conceptualized, and a competent set of laser/plasma parameters in achieving significant amplification is configured. The limitations and plausible rectification for a practical execution of the resonant BRA have also been discussed.

X-ray spectra of plasma radiation from laser induced low-power vacuum discharge

The x-ray spectra of plasma radiation in the wavelength range 30–300 Å are studied. The radiation is emitted from plasma of a vacuum discharge with storage energy less than 30 J that is initiated on an Al or Fe cathode by beam from neodymium laser with a power density up to 1012 W cm−2. It is shown that both the spectral composition and intensity of radiation of hot micropinch plasma that is formed in the cathodic jet are determined by the set of the discharge and the laser pulse characteristics. By optimizing these characteristics, a mode of the discharge operation is attainable, in which a significant portion of the radiation energy is located in the long-wave band of the quasi-continuum (230–270 Å and 160–200 Å for Al and Fe cathodes, respectively). That makes it possible to treat such a discharge as an intense source of narrow-band soft x-ray radiation.

Spatiotemporal and spectral characteristics of X-ray radiation emitted by the Z-pinch during the current implosion of quasispherical multiwire arrays

For the first time, a quasi-spherical current implosion has been experimentally realized on a multimegaampere facility with the peak current of up to 4 MA and a soft X-ray source has been created with high radiation power density on its surface of up to 3 TW/cm2. An increase in the energy density at the centre of the source of soft X-ray radiation (SXR) was experimentally observed upon compression of quasi-spherical arrays with the linear-mass profiling. In this case, the average power density on the surface of the SXR source is three times higher than for implosions of cylindrical arrays of the same mass and close values of the discharge current. Obtained experimental data are compared with the results of modelling the current implosion of multi-wire arrays performed with the help of a three-dimensional radiation-magneto-hydrodynamic code.

Probing quantum systems from the inside while producing the world’s shortest optical pulses

In 1964, Professor L.V. Keldysh, with whom I share winning the Lomonosov Gold Medal, published what was to become a very influential paper. In his paper, he developed the theory of multiphoton ionization for atoms and the creation of electron-hole pairs for solids. Fifty years later, we generate the world’s shortest light pulses using electron wave packets that are extracted from rare gas atoms by an intense infrared pulse much as Professor Keldysh described. The ultrashort bursts of XUV radiation from many atoms add coherently to produce intense pulses as short as 65 attoseconds—the current world record. Similar highly nonlinear processes occur in other atoms, molecules and solids. In addition to its importance as a new source of soft X-ray radiation and ultrashort pulses, the radiation generated from ionizing material encodes information on the quantum system from which it was made. By analyzing the XUV radiation, not only can we image molecular orbitals but also determine the band structure of solids.