Management of Material Redeposition Below and Above the Sample for Laser Micromachining of Laser Fusion Targets

Le résumé fourni par la source

Abstract Ultrashort pulse laser micromachining is a commonly used technique in the field of target fabrication for laser fusion experiments. In this context, material redeposition caused by ultrashort pulse laser ablation can greatly reduce the target quality. This work analyzes material redeposition below and above a polymerized Trimethylolpropantriacrylat (TMPTA) film, by applying the Design of Experiments methodology. The mean and interaction effects of four treatment factors on these processes are identified, using a two-level full factorial design. On the one hand, the results indicate that material redeposition below the sample is dominated by the overlap of consecutive pulses, influencing the degree of chipping. On the other hand, the results suggest that redeposition on the sample top is caused by an interaction of successive ablation plumes. Based on these results, we chose machining parameters that reduce redeposition on both sides of the sample. To further reduce the surface roughness on the sample top, we successfully applied the laser polishing technique using MHz and GHz burst pulses to TMPTA. We find that a number of five sub-pulses within one burst is optimal for polishing TMPTA. The work provides valuable insight into the processes of material redeposition below and above the sample, and demonstrates that laser polishing can be applied to TMPTA. The results are essential to meet the stringent cleanness requirements of targets for laser fusion experiments. The methods deployed in this work can be applied to future polymer ablator materials, making it possible to quickly react to changes in the target design.

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