Single crystal silicon is a chemically active semiconductor material with good processing characteristics. With the development of technology, the role of single crystal silicon components in the field of ICF is becoming more and more important. Restricted by traditional processing method and MRF, damage precursors such as scratches and impurities still remain on the surface after processing. That may influence the performance of the elements. In this paper, we study the effect on the surface by two chemical etching methods and the influence on the damage precursors of nano jet polishing. We used HF solution/HNO3 and KOH/ isopropanol to etch the surface of the element. When the etching depth comes to 0.2 μm, pits and scratches could be easily found on the surface. After the etching process, the element was processed by nano jet polishing and the roughness decreased from 1.264nm to 0.986nm.We used nano jet polishing method to process the element polished by MRF in order to research the evolution of comet-tail scratch. The In-situ tracking method was also applied in this study. After the polishing process, the W-D (width to depth ratio) increased from 30.51 to 45.84. The scratch was deactivated and the PTA (photothermal absorption) decreased from 1.5413nA to 1.3500nA. The Ce impurities were also removed. Its concentration decreased from 0.1162mg/L to 0.0005mg/L and the PTA of the element decreased from 0.3044nA to 0.0652nA. From the research, we can easily know that the subsurface damage exposed after the etching process. That may lay the foundation of the nondestructive processing of single crystal silicon. After nano jet polishing process, the quality of the element became better. The roughness and concentration of Ce impurities decreased. The damage precursors were deactivated and the PTA decreased. In a word, chemical etching could expose the surface damage of single crystal silicon and nano jet polishing can improve the laser damage resistance.
The laser damage threshold of fused silica optics is affected by the surface/subsurface defects in optical fabrication and is related to surface contamination. In this paper, the evolution of surface roughness and photothermal weak absorption of fused silica treated by plasma cleaning and ion beam figuring (IBF) is studied. The results show that plasma cleaning has a certain change on the surface roughness of fused silica, while the change of photothermal weak absorption depends on the initial surface quality. The surface roughness of fused silica has a certain regularity after ion beam figuring, and the photothermal weak absorption is basically consistent with the initial.
This article introduces the modification of single crystal silicon cylindrical mirror that combined immersed CCOS polishing with IBF polishing. In the processing of smoothing and modifying, the quality of the mirror’s surface has been further improved. In this experiment, we optimize the CCOS polishing process and improve the traditional CCOS polishing apparatus to polish the single crystal silicon convex cylindrical mirror. During the CCOS polishing process, the parameter were set as follows: pressure 0.4kPa, speed 25 r/min, polishing liquid concentration 4.5% (pH 10), polishing time 20 min. After polishing by CCOS, IBF is used on its heels. The parameter were set as follows: energy 1000-1200eV (Ar+ ion beam with low energy), incident angle of ion beam 90°, polishing time 30 min. The immersed CCOS polishing process and IBF polishing process iterated repeatedly until the surface quality of the single crystal silicon convex cylindrical mirror meets the requirement. After the polishing process, the sub aperture stitching method and Zygo interferometer are used to detect the surface. The PV value of the single crystal silicon convex cylindrical mirror is 0.265 lambda, the roughness is 0.679nm the residual Zernike is 70.5 nm after testing. The errors over the whole frequency band were significantly reduced. It could be seen from the above that the single crystal silicon convex cylindrical mirror had high accuracy and better profile on the surface after polishing process. The error over the whole frequency band also converged obviously. Therefore, the method that had been described in this paper could be used for the surface modification of single crystal silicon cylindrical mirror.