General design and experiment for separated final optics assembly on high energy laser system

•A separated FOA is proposed to manage contaminants in the atmosphere of FOA.•A cleaning system is designed to improve clean status and lifetime of optics.•The experiment demonstrates the cleaning effectiveness of the cleaning system.•The separated FOA can stably operate under a 351-nm laser shot of 6 J/cm2. Final optics assembly (FOA) is paramount to high energy laser system. It took more than ten years for the National Ignition Facility (NIF) and Laser Megajoule Facility (LMJ) to optimize their FOA and improve output capability. However, the final optical damage limited the output capability of the NIF and LMJ. Contamination is the dominant factor which can dramatically reduce their damage threshold. Accordingly, in this work we propose a separated FOA which mainly locates in the atmosphere and is convenient for contaminants sources management. In addition, we adopts an on-line cleaning system to improve clean status of FOA and achieves longevity lifetime of final optics. The experiment result of the separated FOA demonstrates that even more than one thousand particle contaminants are generated by each laser shot of 6 J/cm2, the on-line cleaning system can take major of them away and maintain cleanliness of separated FOA at ISO Class 3. Our separated FOA can stably operate under a 351-nm laser shot of 6 J/cm2 (21.7 ns shaped-pulse), which is significant to improve the output capability of high energy laser system.