Large aperture Nd:glass disk is often used as the amplifier medium in the inertial confinement fusion (ICF) facilities. The typical size of Nd:glass is up to 810mm×460mm×40mm and more than 3,000 Nd:glass components are needed in the ICF facility. At present, the 3ω fused silica glass and DKDP crystal are mainly responsible for the damage of driver used for ICF. However, with the enlargement of the facility and increase of laser shot number, the laser damage of Nd:glass at 1ω waveband is still an important problem to limit the stable operation of facility and improvement of laser beam quality. In this work, the influence of Nd:glass material itself, mechanical processing, service environment, and laser beam quality on its damage behavior is investigated experimentally and theoretically. The results and conclusions can be summarized as follows: (1) It is very important to control the concentration of platinum impurity particles during melting and the sputtering effect of the cladding materials. (2) The number and length of fractural and brittle scratches should be strictly suppressed during mechanical processing of Nd:glass. (3) The B-integral of high power laser beam should be rigorously controlled. Particularly, the top shape of pulses must be well controlled when operating at high peak laser power. (4) The service environment should be well managed to make sure the cleanness of the surface of Nd:glass better than 100/A level during mounting and running. (5) The service environment and beam quality should be monitored during operation.
In SGIII lasers there are large number of transport mirrors in target beam enclosures. Surface contaminations could easily introduce optical damage, and increase laser energy loss under high laser influence conditions. It is significant for lasers to control contamination and maintain cleanliness. In SGIII prototype, the target beam enclosures are test to be seriously contaminated after about two years of routine operations. Volume cleanliness in mirror boxes are monitored through 24 hours before, during and after a shot. Ingredients of particle and organics are tested. Reconstructions are performed on the mirror boxes to remove debris and keep cleanliness for upward facing surface of mirrors effectively. In SGIII facility some contaminations are found in beam enclosures and on the mirrors after several months of test running. Contaminations sources are analyzed to further know about the contamination mechanisms. Some engineering countermeasures are introduced for controlling contamination and keeping cleanliness for optics.
In this paper, the physical models of the code SG99, which is used to simulate the pulse behavior in high power laser system, are presented in details. The experimental results are also presented to show that SG99 is capable of simulating pulse propagation well and yields reasonable results. In the last, some results in design of TIL(Technical Integrated Experiment Line), the prototype of ShenGuangIII, are also introduced.
For studying the diffuse reflectivity of tungsten target surface, a series of experiments of symmetric flat impact between copper flyer and tungsten target has been done on a two stage light gas gun. Argon ion laser with wavelength 514.5 nm was used as light source to illuminate testing point. The laser light scattered from target was collected by a lens and the light power fore-and-after shock compression was measured. The reflectivity of shock- compressed tungsten target surface could be derived through the power of scattered laser light. In these experiments, the shock pressure in tungsten target was limited from 85 GPa to 250 GPa, five pressure points being chosen. The experimental results show: shock compression makes the reflecting ability of target surface lower, and when the shock pressure is higher than 165 GPa, the reducing speed apparently becomes lower. In addition, the experimental conditions are described in this paper, and the results also are discussed.
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