Study on Edge-trimming Experiment of a Reflective Mirror

Edge-trimming experiment of a reflective mirror is carried on in the paper to study the influence of edge-trimming on the surface figure of a reflective mirror. First, the influences of both self-gravity and the supporting method in measuring on the surface figure of the same mirror before and after edge-trimming are simulated. The simulation results show that both self-gravity and the supporting method in measuring have little influence on the surface figure. Second, the real surface figure of the mirror before edge-trimming is calibrated. Third, edge-trimming experiment of the mirror is carried on the ultrasonic grinding machine. Forth, the real surface figure of the mirror with the same effective aperture after edge-trimming is calibrated. The measuring results show that the surface figure of the mirror after edge-trimming is changed greatly in comparison of that of the mirror before edge-trimming: the surface figure of the mirror before edge-trimming is that the root-mean-square value (RMS value) is about lambda/40 (lambda= 632.8nm), while the RMS value of the surface figure of the mirror after edge-trimming is about lambda/15. At last, the mirror is polished again. The final RMS value of the surface figure of the mirror is about lambda/40. The experimental results show that edge-trimming can bring stress to the mirror. Therefore, edge-trimming influences the surface figure of the mirror considerably. The consequent polishing experiment can erase the influence. The experiment shows that edge-trimming can be carried on with the reflective mirror with lower surface precision. The whole experiment will provide some helpful reference on the choice of edge-trimming occasion of the reflective mirror if it is necessary.