Laser-produced Plasma X-ray Source Research Articles

Calibration of image plate and back illuminated charge coupled device detectors at the thermal emission band of high Z target laser produced plasmas (80–800 eV)

We present a systematic method to absolutely calibrate detector efficiency vs photon energy using a laser produced plasma broadband x-ray source, a gold standard calibrated detector, and transmission gratings (TGs) as dispersive elements. Calibration uses one calibrated TG and a calibrated gold standard detector on one channel and a second calibrated TG and a detector to be calibrated on the other channel. Both channels simultaneously view the laser-produced plasma x-ray source from the same angle with respect to the laser beam and the planar target normal. Image plate detectors are calibrated for the first time at photon energies below 700 eV. Single shot simultaneous calibration of several detectors is possible, making this method an efficient and practical way to periodically calibrate detectors, using in-house capabilities of laser laboratories.

X-ray source with quasi-monochromatic parallel beam

In inertial confined fusion experiments, an excellent-performance and high-efficiency X-ray source plays an important role in X-ray radiography schemes. Indeed, it can be used in a variety of X-ray experimental techniques. The mono-chromaticity, flux intensity, degree of collimation (the radiation can be transported long distances without loss), and spot size of the X-ray source affect the quality of imaging. Ray-tracing simulations, which are validated by experimental results, demonstrate that high-intensity collimated X-ray beams can be produced from an isotropic X-ray source. Therefore, a method of improving the performance of an X-ray source from a laser-produced plasma is presented. A spherically bent crystal is used to collimate mono-chromatic X-rays emitted from a laser-produced plasma. Here we design a spherically bent crystal spectrometer system for collimating the laser-produced X-rays. The system performance is experimentally tested at the Shenguang Ⅱ (SGⅡ) laser facility located in Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences. The beam divergence is measured by using a metal grid placed downstream from the crystal, the metal grid that possesses wires with 60 μm in diameter and 127 μm in period. An imaging plate (IP) is placed at various distances downstream from grid. The quality of the generated beam is monitored by measuring the dimensions of the grid image formed by the beam on IP. While the narrow range of wavelength is measured with a spherically bent crystal spectrometer. Experimental results show that the spherically bent crystal spectrometer system can produce quasi-monochromatic (10<sup>-3</sup> < △ <i>λ/λ</i> <10<sup>-2</sup>) X-ray beams with a high degree of collimation (less than 2 mrad divergence), uniform spot size (~500 μm), and a relative tenability in the wide spectral range. The influences of various experimental parameters on the quality of beam collimation are evaluated in two ways. They can be investigated in test experiments by representing the beam divergence distribution as a function of Bragg angle. In another study of the effect of the aberrations, when the incident beam on the spherically bent crystal is not normal, the beam is less collimated in the tangential plane, and out of collimation in the sagittal plane. Following the ray-tracing method, we analyze the diffracted beam divergence produced by the astigmatic aberration. The qualitative conclusion is that the good agreement with the experimental results is obtained. By fully utilizing limited Bragg angle range, the spherically bent crystal spectrometer system can realize collimated diffracted X-ray beams with divergence of less than 1 mrad by using a laser-produced plasma X-ray source under the appropriately experimental parameters.

Laser Produced Plasma X-Ray Sources for Nanoscale Resolution Contact Microscopy: A Candidate in Cancerous Stem Cells Imaging

Plasma X-ray sources for biological microscopy have been produced by focusing single shots from Nd:glass laser onto carbon rod targets at irradiances between 1 × 1013 W⋅cm−2 and 3 × 1013 W⋅cm−2 to expose test objects. The optimum parameters needed for obtaining high accurate information on the samples under test namely: the minimum energies and irradiances at a range of angles between the incoming laser beam and the normal to the resist, the depth of exposure of the photoresist as a function of incident laser energy (and irradiance) were concluded in this work.

Transmission crystal x-ray spectrometer covering the 6 keV–18 keV energy range with E/ΔE = 1800 instrumental resolving power

A high-resolution x-ray spectrometer utilizing a thin quartz transmission crystal and covering the 6 keV-18 keV energy range has been developed and tested. The spectrometer consists of a cylindrically bent crystal in a vacuum housing. The crystal position and the range of Bragg angles that are incident on the crystal can be adjusted to record an ≈4 keV wide spectrum in the 6 keV-18 keV range. The spectrometer is of the Cauchois type and has a compact linear geometry that is convenient for deployment at laser-produced plasma, EBIT, and other x-ray sources. Test spectra of the W L and Mo K lines from laboratory sources have linewidths as small as 11 eV, approaching the natural widths, and instrumental resolving power as high as 1800. Techniques for enhancing the energy resolution are experimentally demonstrated.

Laser-produced plasmas as unique x-ray souces for industry and astrophysics

Laser produced plasma is one of the brilliant x-ray source that has unique capabilities for use in a wide range of science. Here we describe two examples of laser-produced plasma x-ray source application; one is for the semiconductor device industry and the other is for the astronomy. Extreme ultraviolet (EUV) light sources for microlithography are receiving much attention as an industrial application of laser-produced x-ray source. High power and clean EUV light source, 13.5 nm of wavelength, is developed for mass-production of next generation semiconductor devices. Highest EUV conversion efficiency of 4% has been attained by using low-density and minimum-mass tin targets produced by laser-driven explosion of micro-droplet. In addition, it was recently demonstrated that laser-produced x-ray source is very useful to simulate x-ray astronomical phenomena in the laboratory. A 0.5-keV Planckian x-ray source was created with laser driven implosion for producing non-local-thermodynamical-equilibrium (non-LTE) photoionized plasmas, which is a key to understand astronomical compact objects. Laboratory experiment of non-LTE photoionized plasma offers novel test bed for validation and verification of computational codes used in x-ray astronomy.

Development of a Laser-Produced Plasma X-Ray Source for Phase-Contrast Radiography of D-T Ice Layers

Refraction-enhanced X-ray phase-contrast imaging is crucial for characterization of deuterium-tritium (D-T) ice layer roughness in optically opaque inertial confinement fusion capsules. Observation of the time development of D-T ice roughness over approximately second timescales requires a bright X-ray source that can produce an image faster than the evolution of the ice surface roughness. A laser-produced plasma X-ray source is one of the candidates that can meet this requirement. Experiments were performed at the Janus laser facility at Lawrence Livermore National Laboratory to assess the characteristics of a laser-produced plasma X-ray source as a potential backlight for in situ target characterization.

Ray-tracing simulations of a bent crystal X-ray optics for imaging using laser–plasma X-ray sources

Ray-tracing simulations of an optical X-ray system based on a spherically bent crystal operating in Bragg configuration for monochromatic projection imaging of thin samples are presented, obtained using a code developed for that purpose. The code is particularly suited for characterizing experimental arrangements routinely used with laser-produced plasma X-ray sources. In particular, the spatial resolution of the imaging system was investigated and a careful study of the complex pattern of the X-ray backlighting beam was performed.

Table-Top Soft X-Ray Microscope Imaging System with a Laser-Produced Plasma X-Ray Source

We developed laser-produced plasma X-ray sources using femtosecond laser pulses at 10 Hz repetition rate in a table-top size to investigate basic mechanism of X-ray emission from laser-matter interactions and its application to an X-ray microscope. In a soft X-ray region, laser-plasma X-ray emission from a solid target achieved an intense flux of photons of the order of 1011 photons/rad per pulse with duration of a few hundreds ps, which is intense enough to make a clear imaging in a short time exposure. As an application of laser-produced plasma X-ray source, we developed soft X-ray imaging microscope operating at the wavelength of 13.9 nm. The microscope consists of a cylindrically ellipsoidal condenser mirror and a Schwarzschild objective mirror with highly-reflective multilayer. We report results of performance tests and biological cell observations of the soft X-ray imaging microscope with a compact laser-produced plasma X-ray source.

High-resolution spatial characterization of laser produced plasmas at soft x-ray wavelengths

In this article, we describe the setup and application of a system for the spatial characterization of laser-produced plasma x-ray sources. While pinhole cameras are normally used for this purpose, ...

High-power collimated laser-plasma source for proximity x-ray nanolithography

A compact laser-produced plasma x-ray source radiates 1 nm x rays with an average power of 24 W in 2π steradians. The x-ray conversion efficiency is 9% of the laser power delivered on target. The 300 W laser power is generated by a compact diode-pumped, solid-state Nd:YAG laser system. The point source x-ray radiation is collimated with a polycapillary optic to a parallel x-ray beam. The collimated plasma source (CPS) is used to demonstrate proximity x-ray lithography of 100 nm lines with a 16 μm gap between the mask and wafer. The CPS is optimized for integration with an x-ray stepper to provide a complete collimated plasma lithography exposure tool for the manufacture of high-speed GaAs devices.

Compact focusing von Hamos spectrometer for quantitative x-ray spectroscopy

A compact focusing crystal spectrometer based on the von Hamos scheme is described. Cylindrically curved mica and graphite crystals with a radius of curvature of R=20 mm are used in the spectrometer. A front illuminated charge-coupled device (CCD) linear array detector makes this spectrometer useful for real-time spectroscopy of laser-produced plasma x-ray sources within the wavelength range of λ=1.8–10 Å. Calibration of crystals and the CCD linear array makes it possible to measure absolute photon fluxes. X-ray spectra in an absolute intensity scale were obtained from Mg, Ti, and Fe laser-produced plasmas, with a spectral resolution λ/δλ=800–2000 for the mica and λ/δλ=200–300 for graphite crystal spectrometers. The spectrometer has high efficiency in a wide spectral range, it is compact (40 mm diam, 150 mm length), easy to align, and flexible. The spectrometer is promising for absolute spectral measurements of x-ray radiation of low-intensity sources (femtosecond laser-produced plasmas, micropinches, electron-beam–ion-trap sources, etc.).

High-Power Compact Laser-Plasma Source for X-ray Lithography

A compact laser-produced plasma X-ray source that radiates 1 nm X-rays with an average power of 24 W in 2π steradians is presented. The X-ray conversion efficiency is 9% of the laser power delivered on target. The 300 W laser power is generated by a compact diode-pumped, solid-state Nd:YAG laser system. The X-ray source was used to demonstrate X-ray lithography of 75 nm lines. The X-ray source is optimized for integration with an X-ray stepper to provide a complete X-ray lithography exposure tool for the manufacture of high-speed GaAs devices.

Femtosecond x-ray crystallography

This article gives an overview of recent x-ray diffraction experiments with time resolutions down to ${10}^{\ensuremath{-}13}\mathrm{s}.$ The scientific motivation behind the development is outlined, using examples from solid state physics and biology. The ultrafast resolution may be provided either by fast detectors or short x-ray pulses, and the limitations of both techniques are discussed on the basis of state of the art experiments. In particular, it is shown that with present designs, high time resolution reduces the structural information attainable with high spatial resolution, thereby limiting feasible experiments on the ultrashort time-scale. The first experiment showing subpicosecond conformation changes was recently achieved with simple solids using an ultrafast laser-produced plasma x-ray source. The principles of this experiment are described in detail.

Subpicosecond X-ray diffraction study of laser-induced disorder dynamics above the damage threshold of organic solids

Ultrafast disordering in Langmuir–Blodgett (LB) films and TlAP (thallium acid phthalate) crystals has been investigated by optical-pump–X-ray-probe experiments using intense femtosecond laser pulses. A laser-produced plasma X-ray source at 7.12 Å wavelength is used to study atomic dynamics by subpicosecond time-resolved X-ray diffraction. It is found that a drop of the X-ray diffracted intensity appears with time constants from below 600 fs up to a few tens of picoseconds in LB films optically excited at laser fluxes from 1.8 to 27 J cm−2. This loss in the diffracted intensity is understood as a displacement of the diffracting atoms by ∼8 Å from their equilibrium position. The response of the TlAP crystal was significantly slower. The relation to the atomic structure of the materials is discussed.

Scanning photoelectron microscope with a laser-produced plasma X-ray source

Abstract We are developing a photoelectron microscope on a laboratory scale by using a laser-produced plasma X-ray source. It consists of a laser-produced plasma X-ray source, a monochromator with a toroidal mirror and a concave grating, a grazing incidence focusing mirror (Wolter type-I) and a hemispherical electrostatic electron energy analyzer. In this study, we intend to measure photoelectron spectrum images. The X-ray beam spot size was 9 μm×13 μm. An Au evaporated microchannel plate (MCP) was used as a sample.

A slit grating spectrograph for quantitative soft x-ray spectroscopy

In this article we describe a new slit grating spectrograph which is based on an e-beam written 10 000 linepairs/mm freestanding transmission diffraction grating. In combination with a thinned, back-illuminated charge coupled device (CCD), the spectrograph allows for real-time spectroscopy of laser-produced plasma x-ray sources within the wavelength region λ=1–20 nm. Calibration of grating and CCD allow for the possibility to measure absolute photon fluxes, currently within the wavelength region λ=1–6 nm. The compact spectrograph is easy to align and flexible in its use. Absolutely calibrated spectra were obtained from a liquid-jet laser-plasma source in the water window, with a spectral resolution λ/Δλ⩾330 at λ=3.37 nm. A simple change in experimental geometry allowed single-shot spectra to be recorded with λ/Δλ⩾60 at the same wavelength. In addition, spectra from this laser-plasma source were measured within the range λ=9–20 nm.

Sensitivity measurements of a microchannel plate intensified x-ray detector in the 100–1500 eV photon energy range (abstract)

Microchannel plate intensified (MPI) x-ray detectors are commonly used for imaging and spectral measurements in the 100–1500 eV photon energy range. Using a laser-produced plasma x-ray source, we measured the integrated detector response versus incident x-ray intensity and the relative efficiency versus photon energy of a MPI x-ray detector. Two identical 2000 lines/mm transmission grating spectrometers simultaneously record broadband plasma source emission from a tantalum target. The relative efficiency was determined by comparing the spectrum recorded with an absolutely calibrated x-ray CCD reference detector on one spectrometer to the spectrum recorded with a MPI x-ray detector on the other spectrometer. The integrated detector response versus incident x-ray intensity was measured by simultaneously illuminating the CCD reference detector and the MPI detector with step-wedge-filtered magnesium plasma emission. The aluminum step wedge x-ray filters pass the 1s–2p emission lines of H-like Mg at 1470 eV and the 1s2–1s2p emission lines of He-like Mg at 1350 eV, and provide a four order of magnitude range in incident intensity on the detectors.

Development of Laser-Produced Plasma X-Ray Source.

We developed a laboratory used laser-produced plasma X-ray source. Its characteristics concerning X-ray radiation were evaluated for Al, Ti, Fe and Nb targets in a wavelength region from 2 to 18 nm. The experimental results shows that the source has a brightness of 108∼109 photons/0.1 nm/rad2/mm2/shot at a laser intensity of 9×1012 W/cm2 and X-ray radiates with an energy conversion efficiency of about 4%. Futhermore, to demonstrate an application of the source to surface analysis, we constructed an X-ray diffractometer using the source and obtained X-ray diffraction profiles of a periodic Mo/Si multilayer structure.

Laser-based microfocused x-ray source for mammography: feasibility study.

A laser-produced plasma (LPP) x-ray source with possible application in mammography was created by focusing a laser beam on a Mo target. A Table-Top-Terawatt (TTT) laser operating at 1 J energy per pulse was employed. A dual pulse technique was used. Maximum energy transfer (approximately 10%) from laser light to hot electrons was reached at a 150 ps delay between pulses and the conversion efficiency (hard x-ray yield/laser energy input) was approximately 2 x 10(-4). The created LPP x-ray source is characterized by a very small focal spot size (tens of microns), Gaussian brightness distribution, and a very short pulse duration (a few ps). The spectral distribution of the generated x rays was measured. Images of the focal spot, using a pinhole camera, and images of a resolution pattern and a mammographic phantom were obtained. The LPP focal spot modulation transfer function for different magnification factors was calculated. We have shown that the LPP source in conjunction with a spherically bent, high throughput, crystal monochromator in a fixed-exit Rowland circle configuration can be used to created a narrow band tunable mammography system. Tunability to a specific patient breast tissue thickness and density would allow one to significantly improve contrast and resolution (exceeding 20 lp/mm) while lowering the exposure up to 50% for thicker breasts. The prospects for the LPP x-ray source for mammographic application are discussed.

Soft X-Ray Optics. Present Status of the Fresnel Zone Plate and Its Applications.

Fresnel zone plates (ZP's) are now widely used as imaging or focusing optical devices in soft x-ray region. They are fabricated by the semiconductor technology. Since the ideal spatial resolution is almost equal to the outermost zone width, the progress of ZP's completely depends on that of fabrication technology of the ultra-fine structures. The outermost zone width has recently reached 20-30nm. One of the popular applications of the ZP's is to the x-ray microscope. Along with the recent progress in synchrotron radiation sources and laboratory-size laser produced plasma x-ray sources, many x-ray microscopes are in operation or under construction in the world. In this paper, the optical property of ZP's and the present status of the applications are briefly described.