The Fabrication of a High-Precision Rotational Symmetric Hyperboloid Mirror by Magnetron Sputtering with Film Thickness Correction

Abstract

With the rapid development of optical systems, aspheric reflective optics have become more and more widely used because of their advantages in obtaining better imaging quality. Meanwhile, the optical systems have higher requirements in terms of the surface precision of their optical elements. In this study, we proposed an improved profile-coating method to realize a two-dimensional surface correction method on a rotational symmetric hyperboloid mirror. This method used an irregular mask based on a planetary motion magnetron sputtering system to control film thickness distribution. Moreover, film thickness calibration with a step test was carried out to reduce the processing error of the mask. An optical profiler was used in the step test to quantitatively characterize film thickness distribution and a tilt correction was introduced to correct the test error. As a result, an improvement in figure error in the radial direction of 17.7 nm Root Mean Square (RMS) was achieved. According to these optimization methods, the mask was trimmed for film deposition on the spherical surface. Measurement results from the interferometer show that the figure error of film was 16.23 nm RMS, demonstrating the effectiveness of the optimized method for fabricating a rotational symmetric hyperboloid mirror.