A short pulse, high power laser system provides oppor-tunities for producing and diagnosing various kinds of high speed phenomena such as the study of radiative and kinetic properties of laser-produced plasmas. We have developed a high power phosphate glass laser system for laser fusion research at Osaka University. This four beam system de-livers output energy of 2 kJ in 1 ns and output power of over 4 TW in 10 ps. The peak intensity at the focal point reaches ≈5x1017 W/cm2. Characterization of the system performance based on simulation calculations and experimen-tal measurements are described.
KNbO(3) has been found to be phase matchable for type 1 second-harmonic generation up to 2.4 microm at 22 degrees C. The improved Sellmeier equations that correctly reproduce the nonlinear experiments thus far reported in the literature and our new experimental results for harmonic generation of CO(2) laser harmonics between 3.5303 and 5.2955 microm are presented.
The properties of plasmas produced by high power laser were investigated. The electron temperatures of plasmas from different targets were estimated by the measurement of soft x-ray. Time _??_ variations of the reflected laser light from plasma were also investigated. From the time of flight measurements with a Faraday cage and an electrostatic energy analyzer, the different charged ion could be separated and ion temperatures and drift velocities were obtained from their velocity profiles. No influence of laser pulse duration to the temperature was observed in the cases of durations 2 ns, 4 ns and 10 ns. The experimental results for fast rising laser pulse were discussed and compared with those for slow rising one.
The stimulated Brillouin scattering (SBS) reflectivity of bulk fused-silica glass is measured at the wavelength of 1.06 mm. At long pulse pumping using a longer focusing lens, a fused-silica glass shows high SBS reflectivity of approximately over 95% with no damage observation at a pumping energy of 380 mJ in a pulse duration of 15 ns. We have found that the laser-induced damage threshold at a high SBS reflectance condition is due to reduction of the transmitted power to focus. This makes it possible to operate with high performance in all solid state lasers using a phase-conjugated mirror with fused-silica glass.
The development of high power lasers requires highly damage-resistant optical coatings. Present multilayer dielectric coatings, do not have sufficient laser-induced damage thresholds (LIDTs) to pulsed lasers, particularly in the short wavelength region. LIDT strongly depends on the absorption coefficient of optical coatings and the impurities on the optical substrate. The absorption coefficient of optical coatings can be minimized by optimizing the deposition conditions. However, the impurities on the optical substrate cannot be completely removed by standard optical cleaning techniques. In this paper, the significant improvement of LIDT of optical coatings on subsurface-damage removed fused silica glass due to ion beam etching is presented.
A solar pumped laser system with 7%–9% slope efficiencies has been developed. A Fresnel lens (2×2 m, f=2000 mm) is mounted on a two-axis sun tracker platform and focuses solar radiation toward laser cavity, which embraces Cr:Nd:yttrium aluminum garnet ceramic rod. The maximum emitted laser power is 80 W corresponding to maximum total area performance of 20 W/m2 for the Fresnel lens area. This solar laser system would be used as a section of power plant in a magnesium energy cycle as a cost-efficient solar energy converter. Using direct solar radiation into laser, 4.3% net conversion efficiency has been achieved.
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