Shanghai Optical Machinery Institute has made new progress in the study of laser high precision shape modification theory and technology

Recently, the Laboratory of Precision Optics Manufacturing and Testing Center of Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences has made new progress in the research of laser high-precision modification theory and technology. It is proved for the first time that the laser modification technique can achieve the uniform convergence of the errors in the whole band of nanometer precision under the condition of near stress-free. The relevant research results are entitled "Densi-melting effect for ultra-precision laser beam figuring with clustered overlapping technology at. full-spatial-frequency "is published in Optics Express.

With the development of modern optical technology, fused quartz optical components are widely used in high-power laser systems. However, with the continuous improvement of the surface quality requirements of optical components, the current sub-aperture polishing technology inevitably introduces impurity pollution, which seriously affects the performance of components in high-power optical systems. At present, laser processing has the advantages of no contact, no polishing accessories and flexible processing, which is expected to become a key technology to break through the existing processing bottleneck, but the existing laser ablation and laser polishing technology can not meet the accuracy requirements of surface shape and roughness at the same time, which poses a huge challenge to laser ultra-precision machining.

In order to solve the above problems, the "densification and melting" effect was found for the first time in this study, through the volume contraction caused by the densification effect and the surface smoothing caused by the melting effect, the convergence of surface shape and roughness was realized synchronously. This effect breaks the inherent laser ablation "reducing material" modification process, and successfully reveals the nano scale "equal material" modification mechanism. In addition, the study also proposes an overlapping bunching process, which is modified by overlapping scanning of laser processing subregions (removal functions), reducing the control data volume by three orders of magnitude and without introducing scanning mid-frequency ripples. Through the combination of theory and technology, the results before and after laser high-precision modification are compared, and the surface shape RMS is achieved from 0.009λ to 0.003λ (λ = 632.8 nm), the micron-scale roughness is from 0.447 nm to 0.453 nm, and the nano-scale roughness is from 0.290 nm to 0.269 nm. Stress birefringence ranges from 2.79 nm/cm to 3.94 nm/cm (to meet the requirements of optical systems < 5nm/cm), and successfully realizes the laser shape modification technology with nanometer precision and full band error convergence under nearly stress-free conditions, which is of great significance for ultra-precision manufacturing of optical components.

The relevant work has been supported by the key research and development Program of the Ministry of Science and Technology, the National Natural Science Foundation, the Shanghai Qimingxing Sailing Program, and the Youth Innovation Promotion Association of the Chinese Academy of Sciences.

FIG. 1 Schematic diagram of laser modification with convergent frequency error in the whole space; (a) "densification - melting" effect; (b) overlapping bunching processes; (c1, c2) surface shape error; (d1, d2) micron scale roughness error; (e1, e2) nanoscale roughness error (f) power spectral density curve.

Source: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences