Fabrication and test of high-precision off-axis aspheric lens

In order to meet the requirement of high precision and mass manufacturing of large aspheric lens for high power laser device, a novel manufacturing method combining the bonnet polishing(BP) technology and flexible pitch polishing(FPP) technology was explored. Firstly, after the aspheric generating by ultra-precision grinding, the bonnet polishing technology, in keeping the aspherical surface shape, was used to quickly remove the grinding defect layer and improve the roughness of the element so that it can be directly tested by interferometer. Then, the bonnet polishing technology was used to quickly correct the low frequency error. Finally, the flexible pitch tool was adopted to smooth the middle and high frequency error. During the polishing process, the self-built wavefront detection system and the roughness instrument were used to detect the full frequency error of the aspheric element. Based on the above-mentioned fabrication and testing method, a 430 mm430 mm off-axis apherical lens was manufactured, and the results indicate that, after polishing, the PV, GRMS, PSD1 RMS, PSD2 RMS and Rq are 0.1, 5.7 nm/cm, 1.76 nm, 1 nm and 0.6 nm, respectively. In addition, the power spectral density(PSD) curves are below the required evaluation curve. The experimental results show that the full frequency specifications of the off-axis aspheric lens meet the requirements. The manufacturing method is also applicable to the high-precision manufacturing of other types of large aspheric optical elements.