Results of the joint experiment between ILE Japan and NLHPLP/IAPCM China are reported. New optics for improved line focusing, a cylindrical lens array and a deformable mirror, were used in irradiation of x-ray laser targets. Double-pass amplification at 7.9 nm has been demonstrated. Strong lasing at 7.9 nm with approximately 100 (mu) J output energy has been obtained in Ni-like Nd ions by quasi-traveling wave pumping of double targets.
We have successfully demonstrated double pass enhancement of amplified spontaneous emission of soft x rays, 23.2 and 23.6 nm of 3p - 3s transitions in Ne-like Ge, using an x-ray multilayer mirror. In this paper, we report on the fabrication of the mirror and analysis of its damage suffered during the experiments. The mirror used was a Mo-Si multilayer mirror with the reflectivity of 35% at the wavelength of 23.6 nm, deposited by an rf-sputtering system. In the damaged area of the mirror, only the multilayer was locally evaporated and the bare substrate underneath appeared. The size of the damaged area corresponded to the aperture size. We carried out the simulation on the spatial and temporal distribution of the mirror temperature during the experiment. Assuming that thermal x rays enter the mirror with the largest amount of energy among all the fluxes at the early stage of the enhancement, the result of the simulation can explain the damage feature and the temporal profile of the intensity of the amplified spontaneous emissions.
We have obtained improved performance in terms of intensity and beam divergence (6 mrad) at J=0−1 line of a germanium soft x‐ray laser with a curved slab target which compensates beam deflection due to plasma density gradient. At the first stage of this experiment, the pump laser pulse width was 1 ns and the average irradiance on target was 1.7×1013 W/cm2. The lasing performance of the J=0–1 line suggested improvement in efficiency with shorter pulse pumping. In order to optimize the plasma density and temperature profiles of the expanding germanium plasma, we have employed double pulse pumping of 100 ps pulse width with 300 ps separation having a total energy of 300 J. This has resulted in a further improvement in the x‐ray laser intensity and the beam divergence (2 mrad). We also describe briefly the experimental result of Ni‐like collisional excitation lasers having wavelengths of 6–8 nm.
X-ray emission spectra in the wavelength range of 2 - 13 nm from 21 kinds of material (carbon through tin) irradiated either by a 4 J/35 ns slab Nd:glass laser or by a 0.5 J/8 ns Nd:YAG laser were recorded with a grazing incidence spectrometer equipped with a microchannel plate detector. The absolute photon intensities of these spectra were determined by simultaneous measurement of the emission from a molybdenum plasma with the grazing incidence spectrometer and a transmission grating spectrometer. For the carbon plasma, the electron temperature and density are derived from the spectrum and the conditions for intense Lyman (alpha) line are discussed. Finally, we describe the application to an x-ray microscope with the laser-produced carbon plasma.
In this paper, we present recent progress in soft x-ray laser research at the Institute of Laser Engineering. Detailed characterization of the explosive mode Balmer-alpha soft x-ray laser has been made. Extension of the Balmer-alpha laser to a larger gain length product and to shorter wavelengths are being tested.
