Kozo Ando

Soft X-ray lasing in an Al plasma produced by a 6 J laser

For the first time, amplified spontaneous emission of Al ions was observed in a recombining plasma produced by a low-power driving laser of only 6 joules. It had a high gain of 3.4 cm-1 for a soft X-ray wavelength of 105.7 A of Al XI. This lasing was achieved by tightly focusing a pumping glass laser to a line 40 µm wide and 12 mm long onto a slab target. This result can pave the way to a low-power-pumped X-ray laser.

Development of Vacuum Ultraviolet Streak Camera System for the Evaluation of Vacuum Ultraviolet Emitting Materials

Details of the design and development of a bright vacuum ultraviolet Seya–Namioka type spectrometer and streak camera system with reflection-type input optics is presented. The Seya–Namioka spectrometer has a 40 mm by 45 mm holographic grating with a groove density of 600 grooves/mm, linear dispersion of 8 nm/mm, and effective F-number of 4.2. To eliminate loss of light by absorption, the streak camera imaging unit uses Al and MgF2 coated imaging optics with at least 80% reflection from 125–850 nm and has an effective F-number of 4. It is equipped with a synchronized scan unit that can be tuned to 82 MHz and a slow scan speed unit that can measure up to 2-MHz single event. Temporal response of the system at the 20-ns scanning range is evaluated to be around 260 ps.

Intercombination lines in highly charged Al- and Si-like ions

Delayed spectroscopy techniques have been used to study the isoelectronic development for Al-like and Si-like intercombination line wavelengths. The ions studied range from Kr to Nb. The trend established for the quantity (Eobs - Ecalc)/ζ, (E being the transition energy and ζ the effective charge), shows that the available calculated data are not useful in identifying such intercombination lines for high Z ions. In the case of the Si-like intercombination lines the difference in wavelength between experiment and calculation is around 4A for Nb27+ and this difference increases for higher Z ions. The line identifications were aided by recording spectra for different charge state distributions of the ions after the exciter foil. The experiments were done using ion beams from the RILAC accelerator at RIKEN.

High-resolution soft X-ray spectroscopy of 2.3 keV/u N7+ ions through a microcapillary target

X-rays emitted from 2.3 keV/u 15 N 7þ ions transmitted through a highly ordered Ni microcapillary were measured with a high-resolution soft X-ray spectrometer. The highly ordered microcapillary has recently become available employing a nano-lithographic technique. A transmission ratio and charge state distribution of ions through the microcapillary target were found to be consistent with theoretical predictions. A preliminary analysis showed that a series of X-rays from np–1s transitions with n as high as 8 were identified,which is consistent with the classical over barrier model. 2002 Elsevier Science B.V. All rights reserved.

Visible light spectroscopy of Ar6+ ions in high Rydberg states produced with a microcapillary target

We have observed photons in the visible light range emitted from slow (2.0 keV/amu) highly charged Ar6+ ions which have captured one electron and transmitted through a Ni microcapillary target. Observed lines were identified by comparing with an ab initio calculation based on the multi-configuration Hartree-Fock method

Enhancement of soft X-ray emission from Al plasma by pulse train laser irradiation

A novel technique of effectively producing highly charged ions in laser produced plasma is demonstrated. Time-resolved and integrated soft X-ray spectra showed that ionization of Al atoms is greatly promoted up to Al10+ through the use of a pulse train laser even at very low peak power (1011 W/cm2). The X-ray conversion efficiency increased with increasing number of pulses and with decreasing interpulse time. The interpretation of our experimental results is presented.

High-resolution soft X-ray spectroscopy of slow highly charged ions transmitted through a microcapillary target

Abstract To detect weak X-rays with a high-resolution spectrometer, a charge-coupled device was operated in a single X-ray photon detection mode. A procedure to effectively identify single X-ray was established. In the case of 2.3 keV/u N7+ and Ne9+ incidence, X-rays emitted from ions transmitted through a Ni microcapillary target were measured with the spectrometer using the procedure of the single event mode. The signal-to-noise ratio was improved by using the single photon counting method.

Intercombination transitions in beryllium-like and boron-like iron

Beam-foil spectroscopy techniques have been used to study intercombination transitions in Be-like Fe22+ and B-like Fe21+. The method of time delayed spectroscopy was used to identify the Be-like 2s2 1S0-2s2p 3P1 and B-like 2s22p 2P3/2-2s2p2 4P5/2 transitions. Intensity decay curves for these transitions were recorded and level lifetimes were obtained. The latter were found to be 17.5 ± 1.5 ns for the Be-like 2s2p 3P1 level and 14.8 ± 1.0 ns for the B-like 2s2p2 4P5/2 level.

A 10.7-m Grazing Incidence Spectrometer for the Study of Highly-Ionized Atoms

A high-resolution grazing incidence spectrometer has been constructed for the purpose of analysing the spectra of highly-ionized atoms. The diameter of the Rowland circle is 10.7 m and the grazing angle can be varied from 0.5 to 1.0 degrees. The wavelength coverage is from 100 A down to several A. The characteristics of the spectrometer are described here in detail. The shortest wavelength observed in our light source is the 8.34 A line of Al Kα. The resolution is found experimentally to be better than 0.016 A at about 42.2 A, judged from two close lines of the Mo XVII spectrum taken with an entrance slit 3 µm wide and a grating of 300 grooves/mm. This spectrometer is used mainly as a spectrograph, but it can also be used as a monochromator.

The continuing saga of the Si-like intercombination lines in highly charged ions, Si-like rhodium

The 3s(2)3p(2 3)P(1.2)-3s3p(3) S-5(2) intercombination lines for Si-like Rh have been investigated using the techniques of beam-foil spectroscopy. Two lines have been identified as belonging to these transitions having, however, different wavelengths from what would be expected based on published iso-electronic trends. The identifications suggested here are strengthened by requirements on (a) the known fine structure splitting in the ground configuration, (b) an intensity ratio based on branching ratios, (c) similar decay characteristics and (d) expected behaviour of the lines as a function of the ion beam energy