Masaharu Nishikino

X-ray laser beam with diffraction-limited divergence generated with two gain media

We demonstrate an x-ray laser at a wavelength of 13.9 nm with a beam divergence of 0.2 mrad, which is 1.8 times the diffraction limit. The x-ray laser is generated with two gain media; the seed x-ray pulse from the first medium is amplified in the second medium. The effect of refraction on x-ray propagation is reduced by spatially and temporally controlling the injection of the seed x-ray to the second medium.

Demonstration of a fully spatial coherent X-ray laser at 13.9 nm

We have recently reported the successful development of a fully coherent X-ray laser (XRL) at 13.9 nm by an oscillator-amplifier configuration with two targets. In the experiment, a seed XRL beam from the first target is injected into a plasma amplifier at the second target. The observed XRL beam has full spatial coherence and 0.2 mrad of nearly diffraction-limited divergence. In order to improve the output fluence, the amplification properties of the XRL beam have been investigated using various plasma lengths of the second amplifier target. The output energy has been improved by a factor of ten, increasing the length of the gain region to 10 mm, resulting in about 0.2 /spl mu/J of output energy.

Recent progress in X-ray laser research in JAERI

Recent progress in x-ray laser (XRL) research in Japan Atomic Energy Agency (JAEA) is reviewed. The repetition-rate of the x-ray laser has been improved from each 20 minutes to 10 seconds (0.1 Hz) by installing new driver laser, TOPAZ, which allows us to promote the applications of fully spatial coherent 13.9 nm laser in the wide variety of research fields such as material science, single-shot x-ray holography and atomic physics. In order to improve the present performance of the x-ray lasers, we have investigated the possibilities of the enhancement of the peak brilliance using v-groove target and the generation of circularly polarized x-ray laser under a strong magnetic field. Towards shorter wavelength x-ray lasers, we have investigated several schemes. One is the use of reflection of the light by relativistic plasma mirror driven by laser-wake-field, and the other is photo-pumping scheme using Kα emission from a solid target.

Development of a highly coherent x‐ray laser

We have developed a fully coherent x‐ray laser (XRL) at 13.9 nm by a double‐target configuration. In the experiment, a seed XRL beam from the first target is injected into a plasma amplifier at the second target. The amplified XRL beam has full spatial coherence, 0.2 mrad of the nearly diffraction limited divergence, and 25 nJ of the output energy. For various application researches, we improve the output energy and the beam property of the x‐ray laser. The gain‐length product was gL ∼ 8.2, and the maximum output energy of about 1 μJ is achieved. The divergence of the XRL is affected by the refraction influence in the amplifier medium and/or the diffraction by the small size of the gain medium. We made the 2‐D radiation hydrodynamics simulation code in order to investigate the generation of the gain medium plasma and the refraction influence.

Near-field imaging of Ni-like silver transient collisional x-ray laser

We review our recent progress in the development of transient x-ray lasers and of their application to plasma diagnostic. The first observation of C-ray laser emission at the new PHELIX-GSI facility is reported. This TCE X-ray laser will be a promising tool for heavy-ion spectroscopy. We then present the main results obtained at the LULU-CPA facility with a compact high-resolution X-UV imaging device. This device was used to investigate the spatial source structure of the Ni-like silver transient X-ray laser under different pumping conditions. The key-role of the width of the background laser pulse on the shape of the emitting aperture is demonstrated. Finally the imaging device was used as an interference microscope for interferometry probing of a laser-produced plasma. We describe this experiment performed at APRC-JAERI.

Observation of the Ferroelectric Material with Instantaneous X‐ray Laser Speckles

Picosecond x‐ray speckles experiment has been conducted with a simple setup. The source was a compact silver‐plasma‐based x‐ray laser, with a wavelength of 13.9 nm and pulse duration of 7 ps. The sample was a single crystal of BaTiO3, with ferroelectric multi‐domain structure (a/c domains). The matter correlation function, including statistical information of those randomly distributed scatterers (domains here) within the sample, was extracted by deconvolution of the speckle pattern. The instantaneous x‐ray speckle technique has proved to be particularly efficient to be used to observe fast microscopic‐scale phenomena that are hard to access with other methods currently.

Development of a full spatial coherent x-ray laser at 13.9 nm

We have succeeded in developing a laser-pumped x-ray laser with full spatial coherence at 13.9 nm. A highly directed x-ray laser beam with the divergence of 0.2 mrad was generated from the double target experiment, where a seeding light from the first laser medium was amplified in the second medium. The observed divergence is close to the diffraction limited value within a factor of two. The seeding light was amplified in the second medium without refraction influence and the gain coefficient was about 8 cm-1. The gain region of the second medium was far away from the target surface compared with that of the first medium and located in the considerably low density region. From the measurement of visibility, it was found that the spatial coherent length is longer than the beam diameter.