Yoshiro Owadano

Short-pulse generation by saturated KrF laser amplification of a steep Stokes pulse produced by two-step stimulated Brillouin scattering

We propose a new method for generating short laser pulses. It consists of generation of steep pulses and saturated amplification. A steep Stokes pulse created by two-step stimulated Brillouin scattering is amplified with a KrF laser under conditions of strong saturation. Pulse shortening by approximately 40% is achieved by amplification.

KrF laser picosecond pulse source by stimulated scattering processes

A new short-pulse KrF laser source was developed by combining stimulated scattering processes, namely, Raman, Brillouin, and four-wave-mixing (FWM). Short pulses of 1.1 ps were obtained from 4 ns oscillator output. Only two commercial discharge KrF lasers are required for this system. This method is very simple and could be extended to an ArF laser wavelength in principle.

High-intensity short KrF laser-pulse generation by saturated amplification of truncated leading-edge pulse

Abstract A new method for the generation of high-intensity short KrF laser pulses was developed. The method efficiently uses truncated leading-edge seed-pulse generation by stimulated Brillouin scattering and pulse-shape steepening by saturated amplification, which is mainly based on the Frantz–Nodvik solution. Short KrF pulses of 7 ps were obtained from 20 ns seed pulses without using mode-locked lasers. The experimental results agreed well with the numerical calculations.

Highly Damage-Resistant Reflectors for 248 nm Formed by Fluorides Multilayers

we investigated the laser damage thresholds and optical performances of fluorides multi-layered reflectors, consisting of middle index fluoride and Na3AlF, for high power KrF laser applications. It was found the damage thresholds of those reflectors are significantly improved by laser annealing. Those reflectors with annealing resisted against the fluence of 18-27 J/cm2 (this fluence varies on combinations of various fluorides) for 248 n, 15 nsec, 10Hz pulses.

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 (

Beam smoothing by broadband random-phase irradiation

Abstract A new technique is proposed to achieve smooth laser irradiation profiles on laser fusion targets employing the broad bandwidth of KrF lasers. In this technique, smoothing is obtained by using a spectral dispersing optical device and a random-phase plate placed in front of a focusing lens. Experimental results demonstrate that this simple optical system is effective for smooth irradiation on targets.

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.

High-Repetition-Rate Electron-Beam-Pumped KrF Laser Technology for Inertial-Fusion-Energy Drivers

The development of a high-repetition-rate (rep-rate) electron-beam (e-beam)-pumped KrF laser is described. In this study, we aim to achieve pulsed laser outputs of 20 J/80 ns at a rep rate of 1 Hz. The key issues are heat management in the diode foils and introduction of long-lifetime switches into the pulsed-power system. E-beam generation experiments have been started with initial test results of twenty consecutive shots at 1 Hz. Improvement in the energy-transfer efficiency in the rep-rate pulsed-power systems is also discussed.

Short Stokes pulse generation by mixed Raman gas

Abstract We successfully created a single short Stokes pulse by a newly developed technique that uses mixed gas as a backward stimulated Raman scattering media. Slow rising forward Stokes generation by hydrogen suppresses the later part of the pulse train which usually appears in backward Stokes generation by methane. We demonstrate that a single 67 ps Stokes pulse was generated from a 20 ns KrF laser pulse by the combination of a methane and hydrogen gas mixture.

Effects of Laser Wavelength on Hot Electrons Produced by Ultrashort Intense Laser Pulse on Solid-Density Targets

Hot electron temperatures and electron energy spectra in the course of interaction between intense laser pulse and overdense plasmas are reexamined from a viewpoint of the difference in laser wavelength. The hot electron temperature measured by a particle-in-cell simulation is scaled by