Hidehiko Yashiro

10 kHz 40 W Ti:sapphire regenerative ring amplifier.

A Ti:sapphire regenerative ring amplifier is developed. The power of 40 W before compression and 26 W after compression are achieved at 10 kHz repetition rate. Thermal distortion of a compressor grating is reduced by air flow cooling.

Laser-plasma scanning 3D display for putting digital contents in free space

We present a novel 3D display that can show any 3D contents in free space using laser-plasma scanning in the air. The laser-plasma technology can generate a point illumination at an arbitrary position in the free space. By scanning the position of the illumination, we can display a set of point illuminations in the space, which realizes 3D display in the space. This 3D display has been already presented in Emerging Technology of SIGGRAPH2006, which is the basic platform of our 3D display project. In this presentation, we would like to introduce history of the development of the laser-plasma scanning 3D display, and then describe recent development of the 3D contents analysis and processing technology for realizing an innovative media presentation in a free 3D space. The one of recent development is performed to give preferred 3D contents data to the 3D display in a very flexible manner. This means that we have a platform to develop an interactive 3D contents presentation system using the 3D display, such as an interactive art presentation using the 3D display. We would also like to present the future plan of this 3D display research project.

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.

Use of tin as a plasma source material for high conversion efficiency

Debris-free generation of a tin plasma was demonstrated in the cavity-confined configuration. Narrow band emission at 13.7-nm was observed in an emission spectrum of a cavity confined tin plasma. The spectral efficiency was as high as 12% and we found the conversion efficiency could reach 6%/2π str ultimately while lots of works are required to achieve this value. We also confirmed a magnetic field has some effect of stopping a plasma.

A 37% Efficiency, Kilohertz Repetition Rate Cryogenically Cooled Ti:Sapphire Regenerative Amplifier

We present a high-efficiency Ti:sapphire regenerative amplifier being developed as a pumping laser for a high-brilliance laser-plasma X-ray source operating at a multi-kHz repetition rate. A ring resonator is adopted for stable single transverse mode operation and a laser rod is cryogenically cooled to suppress the strong thermal lens effect. By reducing losses in the resonator and by matching the pumping mode volume with the resonator mode, the conversion efficiency is increased to 37%. The output power is 7.4 W when pumped by a 1 kHz 20 W green laser.

Measurement of Number Density of Water Droplets in Aerosol by Laser-Induced Breakdown

Number density of droplets in an aerosol ejected from a spray nozzle is experimentally measured by laser-induced breakdown. This measurement utilizes the large difference of the breakdown threshold intensities between droplets and air. The volume in which the intensity exceeds the breakdown threshold for droplets is evaluated from the breakdown threshold and the actual laser intensities, and laser focusing parameters. The number of droplets in the volume is evaluated by the breakdown probability and Poisson distribution. This method has high temporal and spatial resolution depending on the laser pulse duration and the laser focusing condition, respectively.

Experimental evaluation of a stopping power of high-energy ions from a laser-produced plasma by a magnetic field

Magnetic field shield for laser produced plasma (LPP) had been investigated. The interaction between expanding LPP and magnetic field is not described by Lorentz force, but, may be described by magneto hydro dynamics. When a magnetic field strength of 0.6T was placed between LPP and a faraday cup, attainment ratio of plasma to a faraday cup was decrease to 20%. The attainment ratio was decreased from 0.4 to 0.25 with varying the distance between the plasma and the magnetic field from 10 mm to 70 mm. And, it was observed that plasma detoured around a magnetic field.

Overview of `Super-ASHURA' KrF Laser Program

Abstract In the Super-ASHURA KrF Laser at ETL, a main amplifier with full pumping duration (270 ns) and 12 beam lines have been completed. At present, total output energy of 2.7 kJ has been extracted from the main amplifier by double-pass amplified 12 beams (20 ns×12) with an aperture filling factor of 74%. Local intrinsic efficiency has reached 10%. In the Raman amplification which is to be used for high peak power pulse generation, multi-pass forward amplification of nanosecond Stokes pulse showed an energy conversion efficiency of 73%. Also, a multi-joule short Stokes pulse (150 ps) has been obtained from 12.5 J, and 20 ns pulse by saturated backward amplification of a self-generated Stokes pulse. To investigate the effect of irradiation smoothness, the two-dimensional profile of the target rear surface displacement has been measured by using short (

Debris-free EUV source using a through-hole tin target

Laser plasma light source using double pulses laser irradiation and through-hole method is proposed as a mass-limited target srouce for extreme UV (EUV) radiation. After minimum necessary material is supplied using the ablation laser from a solid target, only ablated material is irradiated with the heating laser to produce a high-temperature plasma, and EUV radiation is extracted passing through the hole formed in the solid target. Fundamental concept of this scheme, EUV radiation and great reduction of particle debris were experimentally confirmed.

Two-dimensional beam smoothing by broadband random-phase irradiation

A new technique for two-dimensional smoothing is proposed to generate smooth laser irradiation profiles on laser fusion targets employing the broad bandwidth of KrF lasers. In this technique, a wedged etalon is used to get angular dispersion to the orthogonal direction to the one-dimensional broadband random-phase smoothing effect. The preliminary experiment has demonstrated its effectiveness.