Secondary Ion Mass Spectroscopy (SIMS), Electron Probe Micro Analysis (EPMA) and X-Ray Photoelectron
Spectroscopy (XPS) were used to analyze the polishing induced contamination layer at the fused silica optics surface.
Samples were prepared using an MRF polishing machine and cerium-based slurry. The cerium and iron penetration and
concentration were measured in the surface out of defects. Cerium is embedded at the surface in a 60 nm layer and
concentrated at 1200 ppmw in this layer while iron concentration falls down at 30 nm. Spatial distribution and
homogeneity of the pollution were also studied in scratches and bevel using SIMS and EPMA techniques. An
overconcentration was observed in the chamfer and we saw evidence that surface defects such as scratches are specific
places that hold the pollutants. A wet etching was able to completely remove the contamination in the scratch.
Effects of deep wet etching on the surface quality and the laser induced damage probability have been studied on fused
silica samples. Results obtained with a HF/HNO3 solution and a KOH solution were compared on both polished pristine
surface and scratched surfaces. The hydrofluoric solution radically deteriorated the surface quality creating a haze on the
whole surface and increasing considerably the roughness. For both solutions, neither improvement nor deterioration of
the laser damage performances has been observed on the etched surfaces while the laser damage resistance of scratches
has been increased to the level of the surface. We conclude that laser damage performances are equivalent with both
solutions but an acid etching induces surface degradation that is not experienced with basic etching.
We investigate the capacity of magnetorheological finishing (MRF) process to remove surface and subsurface defects of fused silica optics. Polished samples with engineered surface and subsurface defects were manufactured and characterized. Uniform material removals were performed with a QED Q22-XE machine using different MRF process parameters in order to remove these defects. We provide evidence that whatever the MRF process parameters are, MRF is able to remove surface and subsurface defects. Moreover, we show that MRF induces a pollution of the glass interface similar to conventional polishing processes.
In this paper, the nature of the crystalline phases observed at the surface damage sites resulting from laser
irradiation is investigated by X-ray diffraction. The results are compared against new data on thermal decomposition of
KDP salt. The damage sites consist of polycrystalline KDP and partially dehydrated phases. The comparison with the
thermal decomposition study allows to assign a temperature range to the overall temperature reached by the surface
during the damaging process. Finally, the difference between surface damage and bulk damage is discussed.
This study is concerned with the identification of the defects responsible for laser damage observed on
KDP/DKDP frequency triplers used in high power lasers. We reported at BDS 2005 a non destructive high energy X-ray
topographic setup able to characterize lattice imperfections in optics. Results obtained using this technique on KDP and
DKDP crystals are reported and discussed. The influence of each type of defect, observed or likely to exist in optics, is
discussed in light of damage mechanisms recently published. Finally, an experimental setup presumably able to reveal
those defects is proposed.
X-ray diffraction is a non destructive technique used in order to characterize defects in the single crystal. Unfortunately, this analysis can not be performed throughout the whole volume on thick KH2PO4 (KDP) crystals used in the high power lasers systems like NIF and LMJ, these crystals having a thickness close to 10 mm. Considering the usual energy range radiation used for X-ray diffraction and topography (20-30 keV), the beam is rapidly absorbed by the material. However, this problem can be solved by the use of high energy X-ray radiation in order to analyse the complete volume of crystal. The principle of this device will be exposed and preliminary results are shown along with corresponding optical measurements.
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