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We report experiments exhibiting specific features in generating hard x rays with femtosecond laser plasmas as relativistic intensities are approached. Copper foils are irradiated with 1-J/130-fs Ti:sapphire laser pulses, and the x rays are detected with spatial resolution. The results demonstrate a dramatic reduction in the x-ray-emitting spot size at intensities around 10[sup 19] W/cm², and a corresponding increase in the x-ray flux density. These findings are explained in terms of forward acceleration of electrons due to relativistic effects. [ABSTRACT FROM AUTHOR]

Examines the high conversion efficiency generation of kiloelectron volt x-ray from copper and iron targets using krypton fluoride laser plasmas. Determination of conversion efficiencies using aberration corrected focal length lens; Difference in x-ray responsivity for each target materials; Saturation of conversion efficiency at high total energies.

Betatron-type laser-plasma x-rays are recorded simultaneously with their corresponding relativistic electron spectra in a laser wakefield acceleration scheme. The role of the multi-electron gas target in the betatron-type x-ray efficient generation is experimentally examined. A proof of principle experimental study shows that by using a multi-electron gas target and appropriately adjusting the pumping laser intensity an increase in betatron-type x-rays efficiency could be achieved. This is attributed to sophisticated control of the type of the electron injection inside the plasma bubble related to the tunneling ionization process occurring after the laser pulse peak. This method depends primarily on the gas target charge state chosen for attaining the ionization injection scheme and could be extended to a wide range of relativistic laser intensities. [ABSTRACT FROM AUTHOR]

A compact low-energy and high-intensity x-ray source for radiation biology applications is presented. A laser-induced plasma moves inside a 30 kV diode and produces a beam of 1014 electrons at the anode location. An aluminum foil converts a part of the energy of these electrons into x-ray photons, which are characterized using filtered imaging plates. The dose that would be deposited by these x-ray photons in C. elegans larvae is calculated from Geant4 simulations. It can be set to a value ranging between 10 μGy and 10 mGy per laser shot by simply changing the aluminum foil thickness and the diode voltage. Therefore, this versatile and compact x-ray source opens a new path to explore the radiation effects induced by dose rates varying over several orders of magnitude. [ABSTRACT FROM AUTHOR]

Soft x-ray spectra emitted by laser-produced plasmas in the wavelength range 10 Å<λ<250 Å were absolutely measured with a transmission grating and calibrated Kodak 101-01 film. Laser pulses with a length of 3 ns and a wavelength of 0.53 μm were focused at an intensity of 3×1013 W/cm2 on planar targets of various elements with atomic numbers ranging from 4 to 82. The overall conversion of incident laser energy into x-ray energy increases from 2% for Be to nearly 50% for the heaviest elements. [ABSTRACT FROM AUTHOR]

A high average power broadband x-ray source is developed in the multi-keV range, based on the thermal emission of plasmas produced with a 1 kHz fs laser focused on high Z element target. This compact ultrafast x-ray source is used to measure the x-ray absorption near-edge spectroscopy of aluminum K-edge (1.559 keV) with noise lower than 1% of the absorption edge when accumulating laser shots over a few tens of seconds. That demonstrates its suitability to study atomic and electronic structures of matter during ultrafast phase transitions among solid, liquid, or higher energy density states. [ABSTRACT FROM AUTHOR]

In order to demonstrate silica nanomachining, the authors fabricated line-and-space contact masks with spaces of 53 and 70 nm on silica glass plates, followed by irradiation with laser plasma softx rays (LPSXs) with wavelengths around 10 nm. Trenches with the narrowest width of 54 nm and an aspect ratio of ∼1 were fabricated by the LPSX irradiation through the contact masks. It was also clarified that silica glass can be machined by irradiation with LPSXs in the wavelength range of 6–30 nm in Ar gas which was used as an x-ray bandpass filter. [ABSTRACT FROM AUTHOR]

Demonstrates a coherent laser-plasma point x-ray source in the water window spectral region. Filtration of the emission from the source; Generation of monochromatic radiation; Attainment of soft x-ray fringes; Application of the source as hologram or transmission scanning x-ray micrograph.

X-ray conversion efficiency in a 0.53-μm laser-produced copper plasma is studied in the 1.5–5.0 keV range as a function of laser pulse duration (τL) with a laser intensity of 1×1014 W/cm2. The efficiency increases as τ1.3L at pulse lengths of less than 400 ps. For a 200-ps pulse duration, an enhancement of the conversion efficiency is observed with the use of a prepulse. The efficiency is found to be proportional to the scale length of a preformed plasma. Enhancement of a factor 3 is observed for the shots with a prepulse. [ABSTRACT FROM AUTHOR]

Investigates the enhancement in x-ray generation from a laser-produced plasma with a porous silicon (Si) target. Details on the energy penetration depth; Relevance of a porous Si target on pre-pulse intensity requirement for x-ray generation; Effect of pre-pulse intensity on x-ray generation.

Examines the hard-X-ray radiation from short pulse Ti:sapphire laser produced plasmas. Irradiation of the solid targets; Observation on the measured dose rates; Application of the scaling law.

Proposes a high-Z mixture plasma as an efficient converter of laser light to x-rays. Enhancement of energy band gap in varying opacities; Use of a blue laser pulse to measure absolute x-ray emission; Calculation of the Rosseland mean opacity on the basis of the average-atom model.

We perform a comparative study of hard x-ray emission from femtosecond laser plasmas in 15 μm methanol microdroplets and Perspex target. The hard x-ray yield from droplet plasmas is ≃68 times more than that obtained from solid plasmas at 2×1015 W cm-2. A 10 ns prepulse at about 5% of the main pulse appears to be essential for hard x-ray generation from droplets. Hot electron temperature of 36 keV is measured from the droplets at 8×1014 W cm-2, whereas a three times higher intensity is needed to obtain similar hot electron temperatures from Perspex plasmas. Particle-in-cell simulations with very long scale-length density profiles support experimental observations. [ABSTRACT FROM AUTHOR]

We have investigated direct micromachining of quartz glass, using pulsed laser plasma soft x-rays (LPSXs) having a potential capability of nanomachining because the diffraction limit is ∼10 nm. The LPSX’s were generated by irradiation of a Ta target with 532 nm laser light from a conventional Q switched Nd:YAG laser at 700 mJ/pulse. In order to achieve a sufficient power density of LPSX’s beyond the ablation threshold, we developed an ellipsoidal mirror to obtain efficient focusing of LPSXs at around 10 nm. It was found that quartz glass plates are smoothly ablated at 45 nm/shot using the focused and pulsed LPSX’s. [ABSTRACT FROM AUTHOR]

A compact, high-repetition rate, ultrashort-pulse laser-driven hard-x-ray source based on the combination of a femtosecond laser system with an x-ray diode is demonstrated. A comparison with available laser-plasma sources is presented. Numerical modeling is performed which proves that picosecond and subpicosecond hard-x-ray pulses can be produced with this source. [ABSTRACT FROM AUTHOR]

We have used laser-produced plasmas as a broadband source of soft x rays to measure the normal incidence reflectance of multilayer mirrors in the 10–25 nm spectral region. The measurements have a spectral resolution of 0.03 nm and a reflectance resolution of 10%. Measurements made on a Mo/Si multilayer show excellent agreement with results obtained using a synchrotron and indicate a normal incidence peak reflectance of over 50% at 15 nm. By repeating the reflectance measurement at different positions across a single 7.5 cm mirror we determined multilayer uniformity as a function of position and we relate this dependence to the geometry of the deposition process. [ABSTRACT FROM AUTHOR]

We present an indirect method to diagnose the electron beam behaviors and bubble dynamic evolution in a laser-wakefield accelerator. Four kinds of typical bubble dynamic evolution and, hence, electron beam behaviors observed in Particle-In-Cell simulations are identified correspondingly by simultaneous measurement of distinct angular distributions of the betatron radiation and electron beam energy spectra in experiment. The reconstruction of the bubble evolution may shed light on finding an effective way to better generate high-quality electron beams and enhanced betatron X-rays. [ABSTRACT FROM AUTHOR]

An investigation on temporal and spatial properties of hard x-rays (15–88 keV) emitted in a 5.3 kJ plasma focus using Si pin diodes and a pinhole camera is reported. The maximum yield of hard x-rays of 15–88 keV range is estimated about 4.7 J and corresponding efficiency for x-ray generation is 0.09%. The x-rays with energy >15 keV have 15–20 ns pulse duration and ∼1 mm source size. This radiation is used for contact x-ray imaging of biological and compound objects and spatial resolution of ∼50 μm is demonstrated. [ABSTRACT FROM AUTHOR]

The influence of an ultrashort prepulse on K-shell x-ray line emissions from Al plasma produced by 100 fs Ti:sapphire laser pulses is studied. By introducing an independent 100 fs prepulse, a more than 20-fold enhancement in K-shell emission was achieved. We could experimentally optimize K[sub α] and He[sub α] line emissions. In case of oblique incidence, resonance absorption made it possible to maximize K[sub α] emission while keeping pulse duration short. On the other hand, He[sub α] line emission was maximized when a separation between two laser pulses was large, resulting in pulse broadening (∼30 ps). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a method of controlling opacity and gain coefficients of soft x-ray transitions. Utilization of the ion dilution in controlling soft x-ray gain coefficients; Rise of the gain coefficients with the use of composite materials as targets; Increase of the strength of the absorption with the reduction of carbon atoms composition.

An accelerator-based MeV ultrafast electron microscope (MUEM) has been proposed as a promising tool to the study structural dynamics at the nanometer spatial scale and the picosecond temporal scale. Here, we report experimental tests of a prototype MUEM where high quality images with nanoscale fine structures were recorded with a pulsed ∼3 MeV picosecond electron beam. The temporal and spatial resolutions of the MUEM operating in the single-shot mode are about 4 ps (FWHM) and 100 nm (FWHM), corresponding to a temporal-spatial resolution of 4 × 10−19 s m, about 2 orders of magnitude higher than that achieved with state-of-the-art single-shot keV UEM. Using this instrument, we offer the demonstration of visualizing the nanoscale periodic spatial modulation of an electron beam, which may be converted into longitudinal density modulation through emittance exchange to enable production of high-power coherent radiation at short wavelengths. Our results mark a great step towards single-shot nanometer-resolution MUEMs and compact intense x-ray sources that may have widespread applications in many areas of science. [ABSTRACT FROM AUTHOR]