Short-wavelength X-ray Research Articles

Short wavelength X-ray emission generated by high intensity laser irradiation on Xe clusters

We extend the study of the short wavelength X-ray emission from inner-shell excited states in high-density hot plasmas generated by high intensity laser irradiation on Xe clusters. We discuss the effects of electron densities and temperatures on the X-ray emission. The X-rays are emitted from the inner-shell excited state of highly charged ions (Xe35+) only for the density of more than 3×1023 cm−3 and temperature of more than 5 keV though this density is much larger than that simulated by Ditmire et al. [Phys. Rev. A 53 (1996) 3379]. The X-ray intensity depends on the life-time of the inner-shell excited states.

On the spectral resolution of a focusing Bragg spectrometer

The influence of the intensity profile of a wave, focused upon backscattering from a bent crystal, on the spectral resolution of a focusing Bragg spectrometer dynamically reflecting short-wavelength X-ray radiation (λ∼1 A) is considered in comparison to a nonfocusing flat-crystal spectrometer. Conditions necessary for resolving spectral lines in the spectrometers of both types are formulated.

High-resolution X-ray emission Lα1 and Lβ2 Spectra of Hf, Ta, W, Re, and Os

The shape and relative intensities Sα=I(α1s)/I(α1s), Sβ=I(β1s)/I(β2) of the short-wavelength X-ray Lα1 and Lβ2 satellites arising from the radiative decay of the states corresponding to L3M4,5 configurations were investigated experimentally for Hf, Ta, W, Re, and Os. It was established that, in the case of W, the values Sα=2.5%, Sβ=4.2% are five to seven times larger than those for Hf and Ta, and by (30–60)% smaller than those for Re and Os. On the basis of the obtained values of Sα,Sβ, as well as the observed two-component structure of the Lα1 and Lβ2 satellites, it is concluded that the Coster-Kronig L1-L3M5 transitions (CK) are allowed by the energy conservation law even for tungsten, and, starting with this element, they represent a major channel of generation of the states of LL3M5 configuration. Possible features of such a process for the W atom are discussed in comparison with those for Re and Os.

Nanofabrication and diffractive optics for high-resolution x-ray applications

Short wavelength x-ray radiation microscopy is well suited for a number of material and life science studies. The x-ray microscope (XM1) at the Advanced Light Source Synchrotron in Berkeley, California uses two diffractive Fresnel zone plate lenses. The first is a large condenser lens, which collects soft x-ray radiation from a bending magnet, focuses it, and serves as a linear monochromator. The second is the objective zone plate lens, which magnifies the image of the specimen onto a high-efficiency charge coupled device detector. The objective lens determines the numerical aperture and ultimate resolution. New objective lens zone plates with a minimum linewidth of 25 nm and excellent linewidth control have been fabricated using Berkeley Lab’s 100 keV Nanowriter electron beam lithography tool, a calixarene high-resolution negative resist, and gold electroplating. Although the condenser zone plate is less critical to the resolution of the instrument, its efficiency determines the flux on the sample and ultimately the exposure time. A new condenser zone plate was fabricated and has a 9 mm diameter, 44 000 zones, and a minimum zone width of 54 nm (optimally the condenser and objective should have the same zone width). It is also fabricated with the Nanowriter at 100 keV using poly(methylmethacrylate) resist and nickel electroplating. The phase shift through the nickel absorber material enhances the diffraction efficiency over an amplitude only zone plate. To evaluate the microscope’s performance transmission test patterns have been made and imaged. Lineout data show modulation for 30 nm lines and 60 (1:2) spaces to be almost 100%. These new diffractive optical elements represent a significant advancement in the field of high-resolution soft x-ray microscopy. Diffractive optical elements have been used to measure the wave front error of an extreme ultraviolet projection optical system. The reference wave is generated by the spherical wave generated by diffraction from a small freestanding pinhole.

Internal atomic distortion and layer roughness of epitaxial SiC thin films studied by short wavelength X-Ray diffraction

Epitaxial silicon carbide thin films grown on a silicon substrate were examined by short wavelength ( 0.71 A from a molybdenum anode) x-ray diffraction to study their atomic distortion and internal layer roughness. Up to 5 order Bragg peaks along (100) were measured and crystallographic structure factors were obtained. Electron density distributions along the surface normal were reconstructed via Fourier transform. In comparing to the ideal situation, it was found that, due to the lattice mismatch, the silicon atoms are no longer fixed on the same atomic plane, thus the corresponding electron distribution maxima were broadened. Also, the maxima for carbon atoms are flattened, indicating the randomized locations.

On the Estimation of the Termination Effect in Fourier Synthesis in X-ray Structure Analysis

An accurate structure analysis of a spherical LaB6single crystal has been performed with the use of short-wavelength X-rays (WKα1) in order to estimate the termination effect in Fourier synthesis on the electron-density distribution (EDD). It is concluded that the effect on the EDD is negligible if data are taken up to \sin \theta /\lambda =2.0 Å−1, because the negative values disappear completely from the map. The values of displacement parameters of the constituent atoms in LaB6are also discussed.

New prospects for the development of short-wavelength X-ray holography

A description is given of an original proposal to use an analog of a Mach-Zehnder interferometer to record holograms in the x-ray range.

Modeling of ultra-short-pulse laser pumped X-ray lasers

Simple models of ultra-short-pulse laser pumped short wavelength x-ray lasers have been developed. Conditions to obtain gain in the collisional excited Ni-like Ta laser have been estimated for a preformed plasma irradiated by intense laser pulses. In this scheme, preproduction of a high density plasma is essential. The density should be optimized for fast collisional ionization and excitation, minimum radiation trapping, and stable propagation of the ultra-short-pulse laser. Use of a plasma confined in a cylinder is proposed.

MEM Analysis of Electron-Density Distributions for Silicon and Diamond using Short-Wavelength X-rays (W Kα 1)

Short-wavelength X-rays (W Kα1: λ = 0.209 A) have been used to collect higher-order reflections for studies of the electron-density distributions of silicon and diamond with high resolution. The sp3 bonding electron-density distributions of these materials are visible in the total electron-density maps synthesized by the maximum-entropy method (MEM) and also in the difference MEM maps synthesized by Fourier summation of Fmem(h) − Fcore(h), where Fmem(h) is the structure factor calculated from the MEM map and Fcore(h) is the structure factor calculated from Sicore and Ccore models, if very extensive data sets with higher-order reflections are used. These maps are more informative than the conventional difference Fourier map synthesized by Fourier summation of Fobs(h) − Fcore(h) using the observed structure factor Fobs(h) instead of Fmem(h). The present maps can be compared with certain band-theory calculations.

Spectroscopic investigations of the short wavelength x-ray spectra from X-pinch plasmas

Investigations of X-pinch plasma structure and generation of an accelerated electron beam in the X-pinch using the methods of x-ray emission spectroscopy are discussed. The diagnostics allowed to make an investigation of the x-ray radiation with high spectral and spatial resolution over the spectral range 0.5 to more than 10 Å from a variety of wire materials.

Space- and time-resolved investigation of short wavelength x-ray laser in Li-like Ca ions

We have demonstrated the soft x-ray amplification for lithium-like Ca17+ 4f-3d transition at 57.7 Å with 900 ps, 1.05 μm drive laser pulse. The spatial distribution of the gain coefficient and temporal history of the lasing line emissions were also obtained.

Development Of Robust Multilayer Optics For Use In High-Peak Power Radiation Environments

AbstractIn many applications, x-ray mulhilayer mirrors are exposed to high peak fluxes of x-rays with subsequent damage to the mirror. Mirror damage is a particularly severe problem with the use of multilayers as cavity optics for short wavelength x-ray lasers. Intense optical and x-ray radiation, from the x-ray laser plasma amplifier, often damages the multilayer mirror on time scales of hundreds of picoseconds. The phenomenon of multilayer mirror damage by pulsed xray emission has been studied using short duration (500 psec) bursts of soft x-rays from a laser produced gold plasma. The results of the experiments will be compared with some simple models and the possibility of increasing the damage thresholds of short wavelength multilayer mirrors will be discussed.

Characterizaiton of Kodak 101 Film in the Wavelength Region of 30.ANGS. to 250.ANGS..

Characteristic curves (i. e. γ-curves) of Kodak 101-07 film are reported for X-rays in the wavelength region of 30 A to 250 A. The γ-curve for short wavelength X-rays around 30 A agrees well with the theoretical curve given by Henke and co-workers [J. Opt. Soc. Am. B1 (1984) 818]. However, for long wavelength X-rays around 200 A, the γ-curve has been found to be different from that for short wavelength X-rays around 30 A. The film response for X-rays around 200 A is well explained by a new model, in which two photons are required for one AgBr grain to form a neutral silver atom. It is also shown that the absolute γ-curve can be derived from the relative γ-curve by using the observed AgBr grain size according to the model for the film response.

Short wavelength x-ray laser research at the Lawrence Livermore National Laboratory

Laboratory x-ray lasers are currently being studied by researchers worldwide. This paper reviews some of the recent work carried out at Lawrence Livermore National Laboratory. Laser action has been demonstrated at wavelengths as short as 35.6 Å while saturation of the small signal gain has been observed with longer wavelength schemes. Some of the most successful schemes to date have been collisionally pumped x-ray lasers that use the thermal electron distribution within a laser-produced plasma to excite electrons from closed shells in neon- and nickel-like ions to metastable levels in the next shell. Attempts to quantify and improve the longitudinal and transverse coherence of collisionally pumped x-ray lasers are motivated by the desire to produce sources for specific applications. Toward this goal there is a large effort underway to enhance the power output of the Ni-like Ta x-ray laser at 44.83 Å as a source for x-ray imaging of live cells. Improving the efficiency of x-ray lasers in order to produce saturated output with smaller pump lasers is also a goal of this work.

Real and momentum space focusing of neutrons by a cylindrically bent silicon crystal

The optics of Bragg reflection is treated with respect to easy control of the resolution and achievement of a maximum luminosity of crystal diffraction devices. The presented experimental data indicate possibilities for advantageous employment of bent Si crystals with respect to the mosaic ones. Some of our results can be directly applicable in diffractometry with short wave-length X-rays or synchrotron radiation.

The effect of prepulse on X-ray laser development using a powerful subpicosecond KrF laser

A high power UV laser has been developed as a pump source for short wavelength (down to 1 nm) X-ray lasers. Various schemes are considered and theoretical analysis is discussed. Spectroscopic studies of laser-target interaction have been performed and, in particular, the effect of a prepulse on plasma generation has been investigated. Analysis of the observed spectra indicates that reduction of the prepulse energy results in a higher temperature plasma. Investigation of the interaction using thin layered targets is also presented. These data provide evidence for initially hot plasma conditions generated from target layers ≦150 Å. Discussions of proposed laser schemes at 1–5 nm are presented.

Generation of XUV Spectra by Powerful Picosecond Laser

AbstractThe development of laser action at wavelengths shorter than those of current X-ray lasers is being investigated along two fronts. In the first case, we are exploring the possibilities for laser action at 15.4 nm in Li-like AIXI and 12.9 nm in Li-like SiXII in a magnetically confined recombining plasma. Previous work on hydrogen-like carbon, CVI, led to lasing action at 18.2 nm. Recently, this has been applied to microscopy and first results from a soft X-ray laser microscope are presented. A new technique to generate shorter wavelength X-ray lasing involves the interaction of a high power laser with a preformed plasma. The Powerful Picosecond Laser (PP-Laser) System with an output power level of 20-30 GW and focussed power density of 1016- 1017W/cm2has recently become operational. The spectra of highly ionized atoms in the XUV region were recorded on a high resolution grazing incidence spectrometer for the PP-Laser beam interacting with different solid targets.

The axial velocity spread acceptance of free electron lasers and its application to X-ray FEL design

We present various criteria for the definition of axial velocity spread acceptance of free electron lasers (FEL), and provide analytical approximations, numerical calculations and design curves for this parameter in the low, high, and intermediate gain regimes. This parameter is used to calculate the energy spread acceptance, emittance acceptance and other e-beam quality parameters. A special emphasis is put on the design considerations of short wavelength (X-ray) FELs. For this reason, the parameter calculation in this work is limited to the tenuous beam regimes only, and parameters are calculated for intermediate and moderately high gain regimes, which correspond to the low quality factor of X-ray resonators in the present state of the art.

Soft and Ultrasoft X-Ray Fluorescent Spectrometer Using Total Reflection Monochromator

Since specular reflection of characteristic X-rays can become nearly total external reflection at grazing incidence, total reflection analysis offers an alternative to the wavelength dispersive method based on Bragg reflection. Using curves of calculated and measured intensity versus glancing angle, a high-efficiency mirror material was selected and the optimized optical geometry and filtering conditions were determined. Short wavelength X-rays could be eliminated and overlapping interference of equal and longer wavelength X-rays was excluded using the equation for determining the element concentration. Analytical examples for Al, C and B are described.

D-region recombination coefficients and the short wavelength X-ray flux during a solar flare

VLF phase and amplitude measurements were made on five different frequencies at São Paulo, Brazil during a solar flare which occurred on 22nd January 1972. The phase and amplitude measurements during the decay phase of the flare were combined with the full wave solutions of Wait and Spies (1964) to calculate the recombination coefficient in the lower ionosphere. The values thus obtained are lower than those reported by Reid (1970), but are compatible with those reported by Montbriand et al. (1972) during Solar X-ray events. The effective loss rates have been utilized to calculate the ion-production at the maximum of the flare, which in turn has been utilized to calculate the incident X-ray flux as a function of wavelength at the maximum of the flare. Extensions to the calculations are discussed.