Coarse Phasing Detection Using Multiwavelength Wavefront

Abstract

Presently, the segmented mirror is the mainstream development direction of large-aperture telescopes. The key problem affecting the performance of segmented mirror telescopes concerns the co-phase of the segments. The segments’ co-phase includes the fine phasing stage with high detection accuracy requirements and a small measurable range, and the coarse phasing stage with relatively high detection accuracy requirements and a large measurable range. For interferometry, the required accuracy of the transition from the coarse phasing stage to the fine phasing stage is half of the measured wavelength (~300 nm). In this study, a piston measure method based on the wavefront data of the interference measurement results of multiple different wavelengths is proposed. The simulation results show that the method can achieve a measurement accuracy of more than 300 nm in a large range of 1 mm. The experimental results show that the method can achieve a more-than-300-μm measurable range and approximately 1.5 μm detection accuracy under laboratory conditions; this method has advantages in terms of the measured range and speed and is suitable for the coarse phasing stage.

Keywords

• segmented mirrors
• large aperture telescope
• interferometry
• active optics
• wave-front sensing