Plasma X-ray Source Research Articles

A Gated, Four-frame Pinhole Camera with Quantitative Image Acquisition

A gated, multiframe microchannel plate soft X-ray sensor with quantitative acquisition has been developed. The system is composed of an image acquisition system and a gated pinhole camera capable of taking four successive frames at a time resolution of ∼220 ps. The response of the system has been quantitatively investigated. To perform a quantitative evaluation of the captured X-ray images, the image acquisition and measurement of the phosphor current are executed simultaneously in the experiment. The system has been examined using a plasma X-ray source generated by a plasma focus device with an additional gas puff. The compression and bifurcation process of plasma hot spots in a neon puffed experiment has been successfully recorded. Quantitative analysis of the images indicates that an order of 1016 photons/(s·mm2·mrad2) emissions originate from the plasma in a soft X-ray region 6–14 Å.

Laser-induced Plasma X-ray Source and Its Applications. Debris-free Gas Puff Laser Plasma X-ray Source.

Laser plasma X-ray sources are currently used for various applications as a high-brightness source. The main problem, however, is the debris production from the source that causes degradation of the X-ray optics. To overcome this problem we pick up a high pressure gas-puff target created by pulsed injection of high-density gas through a nozzle. Measurements of X-ray spectra from the plasmas produced by using a gas puff target irradiated with a Nd: YAG laser are described. The obtained results would also allow to develop an efficient and debrisless laser-produced X-ray source to be used for the applications in various fields.

Laser-induced Plasma X-ray Source and Its Applications. Laser Plasma X-ray Source and Its Future Prospect.

Physical mechanisms and characteristics of X-ray generation in laser plasmas are reviewed including atomic number dependence of X-ray conversion efficiency. The critical issues for laser plasma X-rays to be of practical use are debris and continuous supply of target materials. Cryogenic target and gas puff target are discussed and their future prospects are also discussed.

Development of low-energy X-ray fluorescence micro-distribution analysis using a laser plasma X-ray source and multilayer optics

A new technique is presented for low-energy X-ray fluorescence micro-distribution analysis of low-Z elements at micrometer spatial resolutions. The technique is based on the use of a laser plasma X-ray source and spherically curved multilayer optics. A large collimator is used to focus the light from the laser plasma on the sample and a Schwarzschild mirror set is used to image the fluorescent radiation on a 2D CCD unit. A first system, now under development, is designed for detection of the carbon Kα-line. The system consists of a Cr/Sc collimator of 260 mm diameter, focusing 0.7 sr of the light from the plasma on the sample, and an Fe/C Schwarzschild mirror set with 20× magnification for detection of the carbon in the sample. A resolution in the micrometer range is expected to be achievable, with a detection limit of a few per cent. Upgrading of this system is expected to result in sub-micrometer resolution and a detection limit in the ppm range.

Laser-induced Plasma X-ray Source and Its Applications. Time Resolved Measurement of Laser-Ablated Particles by LAPXAS(Laser Plasma Soft X-ray Absorption Spectroscopy).

The time-and spatially-resolved properties of laser ablated carbon, boron and silicon particles were measured by LAPXAS (Laser Plasma Soft X-ray Absorption Spectroscopy). The maximum speed of positively charged ions is higher than those of neutral atoms and negatively charged ions. The spatial distributions of the laser-ablated particles in the localized rare gas environment were measured. In helium gas environment, by the helium cloud generated on the top of ablation plume depressed the ablation plume. There is no formation of silicon clusters till 15μs after laser ablation in the argon gas environment.

Laser-induced Plasma X-ray Source and Its Applications. Hard X-ray Generation by Femtosecond Laser Induced Plasma and Picosecond X-ray Diffraction.

Hard X-ray generation by irradiating the femtosecond laser, produced by using a table-top tera-watt laser system, onto metal targets is reported. The X-rays generated from a Cu target has an energy of around 8 keV and a pulse width of 6 ps. X-ray diffraction has been made on a Si(111) surface using the X-ray. A preliminary experiment of picosecond time-resolved X-ray diffraction on the lattice expansion of a Si crystal by 300 ps laser irradiation is demonstrated.

Laser-induced Plasma X-ray Source and Its Applications. Development of Laser-plasma Soft X-ray Source for Projection Lithography.

Laser-plasma soft X-rays as a projection X-ray lithograph source are required to be used for more than 8 successive hours. And serious problems are soft X-ray energy stability, damages to optics by debris and successive supply targets. From the measurements of soft X-ray spectra and amount, size and scattering direction of debris from target irradiated with focused laser, we have developed a laser-plasma soft X-ray source system with debris-shield, debris free X-ray filter, tape-target driver and the low debris tape-target of the thin aluminum and polymer films. We demonstrated 8 successive hours generation of soft X-rays with the developed laser-plasma soft X-ray system as a projection X-ray lithograph source. The energy conversion efficiency of the soft X-rays at the wavelength of 13 nm in our system was estimated to be 0.29%.

Laser-induced Plasma X-ray Source and Its Applications. Soft X-ray from Femtosecond Laser Produced Plasma and Its Application to Material Science.

Laser-induced Plasma X-ray Source and Its Applications. Soft X-ray from Femtosecond Laser Produced Plasma and Its Application to Material Science.

Laser-induced Plasma X-ray Source and Its Applications. Photoelectron Micro-Spectroscopy with a Laser-Plasma X-ray Source.

A photoelectron micro-spectroscopy system with a laser-plasma x-ray source is being developed to achieve a submicron spatial resolution in an in-house system. Although a laser-plasma source has an ultra-high peak brilliance, timeaveraged power is relatively low because its emitting duration is very short and the duty factor is low even at a high-rep rate operation. However, two spectroscopical ideas in our system are making the “source brilliance limited”; spatial resolution of the system very high. One idea is the use of a filter to select a single line from the x-ray source, and the other is the time-of-flight method for the electron energy analysis. Experimental results obtained so far are presented and advantages of our method and future prospects are discussed.

Imaging x‐ray fluorescence spectroscopy using microchannel plate relay optics

A novel imaging low-energy x-ray fluorescence spectrometer with no moving parts, based on a microchannel plate relay optic and an open electrode charge-coupled device with good sub-keV quantum efficiency, is described. Results from a proof of principle experiment using the Rutherford Appleton Laboratory picosecond pulsed laser plasma x-ray source are described and the performance limits of the spectrometer explored. Copyright © 1999 John Wiley & Sons, Ltd.

Imaging x-ray fluorescence spectroscopy using microchannel plate relay optics

A novel imaging low-energy x-ray fluorescence spectrometer with no moving parts, based on a microchannel plate relay optic and an open electrode charge-coupled device with good sub-keV quantum efficiency, is described. Results from a proof of principle experiment using the Rutherford Appleton Laboratory picosecond pulsed laser plasma x-ray source are described and the performance limits of the spectrometer explored. Copyright © 1999 John Wiley & Sons, Ltd.

Laser-induced Plasma X-ray Source and Its Applications. Soft X-ray Imaging Microscope with a Laser Produced Plasma Source.

We constructed a soft X-ray imaging microscope on a laboratory scale by using a laser produced plasma source. Two different soft X-rays (wavelength: 3.2 nm and 5.2 nm) were obtained by using a Nd-YAG laser with a power of 1.2 J and a pulse width of 8 ns. Wolter mirrors were used as a condenser and an objective. A back-illuminated CCD camera was introduced as an X-ray imaging detector. Spatial resolution was estimated to be about 60 nm with a transmission grating object. An X-ray micrograph of a stoma at epidermis of vincia faba L. was obtained. A human red blood cell in a solution was also observed and it showed that the soft X-ray microscope is available for living specimens in a wet state.

X-Ray Engineering and Its Application. Laser Plasma X-Ray Sources.

We briefly describe the present status of laser plasma x-ray sources for various applications. One of the main problems in soft x-ray applications is the production of debris by the source, which degrades the quality of the x-ray optics. To overcome this problem we propose the use of a cryogenic target or a high pressure gas-puff target. The cryogenic target provides x-rays as intense as those from a laser-irradiated solid target. Gas-puff targets are created by the pulsed injection of high-density gas through a nozzle. Experiments with plasmas produced using a gas-puff target irradiated with a Nd: YAG laser are described. The obtained results would allow for the development of an efficient and debrisless laser-produced x-ray source that would be useful for applications in various fields.

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.

Study of second harmonic emissions for characterization of laser–plasma X-ray sources

An investigation of second harmonic (SH) and X-ray emissions from Al plasmas produced by 3-ns, 1.064-μm laser pulses at 1014 W/cm2 is reported. The SH and X-ray yields are strongly correlated as a function of the target position with respect to the laser beam focus. The SH originates from the underdense coronal plasma and has a filamentary source, while the X-ray source is uniform. The results suggest that, although the X-ray emission is significantly enhanced by the filamentation of the laser light in the corona, there is a smoothing effect in the energy transport process toward the overdense region.

Observation of chemical shifts of Si 2p level by an x-ray photoelectron spectroscopy system with a laser-plasma x-ray source

An x-ray photoelectron spectroscopy system with a laser-plasma x-ray source is shown to have energy resolution high enough to observe chemical shifts of Si 2p electrons in SiO2, Si3N4, and pure Si. A boron nitride (BN) plasma x-ray source is produced by irradiation of 100 mJ Q-switched YAG laser pulses. A single line emission at 4.86 nm is selected from the BN plasma by means of carbon foils. Fine spectra are acquired with only 96 laser shots. The results obtained confirm that a laboratory-sized x-ray photoelectron spectroscopy system with submicron spatial resolution and high spectral acquisition speed can be realized.

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.

Metrology and modeling of microchannel plate x-ray optics

A Monte Carlo ray-trace model of nonideal microchannel plate (MCP) x-ray optics is described. The model takes into account angular misalignments, both transverse and axial, between the channels and the multifiber bundles; pincushion distortion of the square channels; radiusing of the channel vertices; and scattering from microroughness of the channel walls. The model also takes into account the spectrum and nonisotropic nature of the illuminating radiation. Using optical, scanning electron, and atomic force microscopies, as well as x-ray scattering data obtained with a laser plasma x-ray source, we have determined a partial error budget for the focusing action of a real square-pore MCP, leaving only the interchannel long-axis misalignment to be found by comparison of simulated and measured images. The power of the Monte Carlo model in directing the future development of MCP optics is illustrated.

X-ray emission from plasmas generated by 450 femtosecond excimer laser pulses

A plasma x-ray source is generated using a 10 mJ, 450 fs KrF excimer laser pulse focused onto a copper target at intensities up to 1.6 × 1015 W/cm2. The energy conversion efficiency from 248 nm laser light to x-rays in the range from 1 keV to 1.4 keV is measured as a function of the laser energy onto the target. The maximum observed efficiency is 0.5% for 5 mJ incident laser energy. The obtained results are compared with efficiencies observed using longer laser pulses of the same wavelength and intensity onto the target.

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.