Sub-nanometer displacement measurement vortex interferometer combining speckle-based feedback alignment and global Zernike fitting

Vortex beam-based interferometric measurement technology is widely utilized in high-precision displacement measurement. However, beam misalignment leads to interference pattern distortion, introducing significant measurement errors. To address this, we propose a vortex interferometer based on speckle-correlation feedback alignment and global Zernike polynomial fitting. First, a speckle-based automatic beam alignment system is implemented for real-time correction to ensure interference pattern quality. Second, aberrations are eliminated through global Zernike polynomial fitting, and the piston term is extracted for displacement calculation. In 10 nm step tests conducted under both misaligned and automatically aligned states, the residual standard deviation decreased from 3.85 to 0.517 nm. Experimental results demonstrate that the interference quality is restored, achieving sub-nanometer measurement precision.