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[en] Coherent x-ray and its applications are expected as new scientific fields in near future. We have succeeded in developing a soft x-ray laser with full spatial coherence for the first time. This x-ray laser, which is monochromatic light with the wavelength of 13.9 nm, has temporal duration of a few pico-second and remarkable beam divergence of 0.2 mrad. We developed an experimental device for generating nano scale x-ray laser beam using Fresnel zoneplate. From numerical analysis for the focusing property, it is found that this device generates an x-ray intensity of about 5x10¹⁴ W/cm². (author)

[en] A laser-pumped x-ray laser with full spatial coherence has been developed for the first time. This x-ray laser has a wavelength of 13.9 nm and a beam divergence of 0.2 mrad. In the experiment, a seeding light from the first laser medium was amplified in the second medium, which worked as an active spatial filter. The observed beam divergence was close to the diffraction limited value within a factor of two. The seeding light was amplified in the second medium without refraction influence. The gain region of the second medium was far away from the target surface compared with that of the first medium, and was located in a region of considerably low density. From the measurement of visibility, it was found that the spatial coherent length was longer than the beam diameter. This means that this x-ray laser beam has full spatial coherence. (author)

[en] The initial imprint of density perturbation due to spatial non-uniformity of laser intensity is one of the most important issues in laser fusion research. The imprint mitigation scheme by use of soft x-ray radiation has been proposed to reduce the laser non-uniformity through the thermal conduction region. We present the results of two-dimensional simulation concerning this issue using our integrated code. (author)

[en] The initial imprint of mass perturbation due to spatial nonuniformity of laser intensity is one of the most important issues in laser fusion research. Several imprint mitigation schemes by the use of soft X-ray radiation have been proposed to enhance the thermal smoothing effect within the conduction region. One of the schemes uses external X-ray irradiation prior to laser incidence to produce preformed plasma. Another has a low-density foam layer and high-Z material to heat the foam radiatively and make it uniform in density. (author)

[en] The soft x-ray laser, 13.9 nm in wavelength, with full spatial coherence has been focused with a Fresnel zoneplate (FZP). The soft x-ray laser is generated with two gain media. The energy of the soft x-ray laser is about 2 μJ and the beam divergences at vertical and horizontal direction are 0.4 mrad and 2.3 mrad, respectively. We calculate numerically a far field image of the diffraction at about 480 mm after the FZP. A good agreement is obtained in the comparison between measured and calculated images. From the calculation, the intensity and diameter of the focused beam are estimated to be 3x10¹⁰ W/cm² and 140 nm, respectively. (author)

[en] We report the observation of electron density dip in a laser-produced molybdenum plasma pumped by double laser pulses which are linearly focused on the molybdenum slab target. The observed density dip was clearly formed at the time of 1 - 1.5ns after the second pulse, and the electron density of the dip was around 2x10¹⁸ cm^-3 to 5x10¹⁸ cm^-3. The probe beam injected into the plasma column in the longitudinal direction was guided with the plasma length of up to 4.3 mm. The experimental result implies that the obtained plasma can be used as the pre-formed plasma for the axial pumping x-ray laser scheme. (author)

[en] A joint research project between ILE Osaka and JAEA Kansai has been carried out since FY2006. The project is entitled 'PW laser driven monochromatic quantum beam science' to improve understanding of physics in intense radiation and energetic particle beam generations, and to explore new fields including industrial and bio-medical applications. The project team is organized by four teams; monochromatic particle beam generation, monochromatic x-ray generation, terahertz radiation from plasma, and new laser technologies aiming at exa-watt lasers. In this report, we will describe recent progress on the x-ray generation and bio-medical applications. (author)

[en] A plasma medium for x-ray lasers by means of transient collisional excitation has been investigated with a two-dimensional radiation hydrodynamics code. The propagating x-ray laser is refracted in the medium due to the gradient of electron number density, which depends on the pumping laser pulse. The numerical results suggest low-density islands that can collimate the laser beam are formed behind a blast wave. (author)

[en] The development of continuous pumping to the target system is an important issue for realizing an x-ray laser with the high repetition rate. We have developed a 13.9 nm XRL using a silver tape target and demonstrated a highly coherent XRL with an oscillator-amplifier configuration using two tape target systems and the TOPAZ laser system with a 10-J and a 0.1-Hz repetition rate. The output energy is comparable to the x-ray laser generated with a silver-deposited slab target, and the pointing stability using the new tape target system is better than conventional slab target. (author)