Enhancing the measurement stability of segmented mirror edge height through synchronous measurement in atmospheric turbulence

Optical interference phase measurement is a crucial technology for measuring the edge height of segments during the co-phased adjustment stage of giant astronomical telescopes equipped with segmented primary mirrors. For the Chinese Giant Solar Telescope (CGST), achieving optical interferometric measurements with a range of 10 <i>µ</i>m or more is a critical challenge that must be addressed to integrate the the co-focus and phasing adjustment processes. Given the unique requirements of solar observation, CGST intends to implement multi-wavelength technology to tackle the measurement range issue. However, this multi-wavelength measurement approach encounters the problem of edge jumps, and merely extending the exposure time does not effectively resolve this issue, which could compromise the telescope's diffraction-limited observational capabilities. The study indicates that the relative measurement error between two wavelengths, caused by atmospheric turbulence, is the primary factor leading to edge jumps. To address this issue, the paper proposes a dual-wavelength synchronous measurement technique. An experiment conducted on a segmented-mirror system demonstrates that, under turbulent conditions and with an exposure time of one second, the probability of edge jumps is negligible. By employing dual-wavelength synchronous technology, each measurement and adjustment takes only a few seconds, allowing the co-phased adjustment of CGST to be completed in just two to three rounds of measurement and adjustment.