Yoshiyuki Hisada

Observation of Gain and Double-pass Amplification of Li-like Al Soft X-ray Transitions in a Recombining Plasma Pumped by a Pulse-train YAG Laser

A pulse-train yttrium aluminium garnet (YAG) laser was used with a shaped envelope, as well as a new lens system for producing a dotted-line irradiation pattern in X-ray laser experiments. Amplified spontaneous emission (ASE) signals of the two Li-like Al transitions (3d-4f, 15.47 nm and 3p-4d, 15.06 nm) were observed with a pumping energy of only 1.5–2 J. The gain coefficient were approximately 3 cm-1 for the 3d-4f line and was maintained for a period of about 1 ns. The double-pass amplification experiment was carried out using a plane multilayer mirror. A clear increase in the above two Li-like Al transition lines was observed. It is highly expected that a strong laser amplification could be achieved in an X-ray laser cavity with two multilayer X-ray mirrors.

Debris from High-Aspect-Ratio Rectangular Focused Laser Irradiation on a Tape Target Surface in an X-Ray Laser System

This study measures the distribution of debris ejected from an aluminum tape target subjected to laser irradiation. The irradiation area is rectangular with a high aspect ratio of 67. The power density of the laser beam is 8×1010 W/cm2 at the irradiation surface. The ejected debris is collected on a plane parallel to the target surface. The angular distribution of debris thickness in the direction parallel to the longer side of the irradiation area is cos 60θh. Similarly, the angular distribution of debris thickness in the direction parallel to the shorter side of the irradiation area is cos 5θv, where the angles θh and θv are deviations from the irradiation surface normal in the horizontal and vertical directions, respectively. An additional feature is the sacrificial film feed mechanism designed to shield the laser beam entrance window from debris deposition. Based on the angular distribution of debris thickness, the film feed rate is adjusted to ensure delivery of the required beam energy at the target surface.

Study of tabletop x-ray laser pumped by a YAG laser

X-ray lasings of Li-like Al ion in the recombination scheme have been investigated using a tabletop pulse-train YAG laser system. Two types of cavity experiments have been carried out, one is an unstable resonator consisting of two flat Mo/Si multilayer mirrors and the other is that with a concave mirror. Clear enhancement in the Li-like Al transition lines at 15.47 nm has been observed for both types of cavities as a high peak in line intensity preceding the plasma emission. The observed feature of the preceding emission can be reproduced by the raytrace calculation.