Measurement of mid-frequency wavefront for large-aperture optics

It has become more important for the accurate measurement of the mid-frequency wavefront of the large-aperture optics in high-power laser systems. The root mean square of mid-frequency wavefront is one of the most important specifications. According to the frequency range of mid-frequency wavefront and frequency response characteristics of the measurement devices, the mid-frequency region can be divided into two separate bands, the low-frequency band and the high-frequency band. The wavefront in different band can be measured by interferomter and optical profiler respectively. The full-aperture mid-frequency wavefront over the low-frequency band can be measured by a large-aperture interferometer. Comparing measurement results of the large-aperture interferometer and the small-aperture interferometer, one method named synthesizing averaging sub-aperture wavefronts is proposed to measure the root mean square of the full-aperture wavefront in the same frequency region. Using discrete sampling method, the mid-frequency wavefront of large-aperture optics over the high-frequency band can be measured by optical profiler. It is experimentally shown that the 33 sampling pattern is enough for the measurement of the wavefront with 410 mm410 mm size.