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SIOM Makes Progress in Adaptive Interferometric Metrology of Freeform Optical Surfaces
Recently, a research team led by Researcher Liu Shijie from the Optical Testing and Characterization Center of the High-Power Laser Component Technology and Engineering Department at the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences (SIOM, CAS), has made new progress in the adaptive interferometric detection of large-deviation freeform optical components. The relevant findings were published in Optics Express under the title "Interferogram-free adaptive wavefront interferometry: fourier spot analysis enhancing adaptive compensation performance".
To address the issue that conventional adaptive wavefront interferometry (AWI) relies heavily on interferogram reconstruction and recognition and thus cannot effectively measure optical components with large surface-form deviations, this study proposed an interferogram-free adaptive wavefront interferometry (IF-AWI) based on Fourier spot (FS) analysis. This method completely eliminates dependence on interference fringes, phase shifting, and phase unwrapping during the adaptive compensation process. By analyzing the intensity distribution of Fourier spots to guide the optimization direction, it enables stable and efficient wavefront compensation and measurement even when interference fringes fail to form or are severely missing.
To further improve optimization efficiency and convergence performance, the research team introduced an intelligent optimization algorithm based on the Runge–Kutta method, which achieves a good balance between global search capability and local convergence speed. This method can successfully compensate freeform wavefronts with a peak-to-valley value exceeding 100λ and a root-mean-square value exceeding 20λ within approximately 60 iterations.
Figure 1 Schematic diagram of IF-AWI principle: (a) Optical path diagram; (b) Schematic diagram of polarization states of reference light and test light.
(P1–3: Linear polarizers, QWP1–3: Quarter-wave plates, L1–3: Lenses, PBS: Polarizing beam splitter, BS: Beam splitter, SUT: Surface under test, S: Aperture stop)
This achievement breaks through the fundamental limitation of traditional adaptive interferometry on the quality of interference fringes, significantly expanding the measurable dynamic range of freeform surfaces. It provides a brand-new technical route for the in-situ detection of freeform surfaces during polishing, and has important application value for the manufacturing and testing of high-end optical components.