Adaptive pinhole point diffraction interferometer based on a liquid crystal on silicon spatial light modulator.

This paper introduces an adaptive pinhole point diffraction interferometer (PPDI) integrated with a liquid crystal on silicon spatial light modulator (LCOS-SLM) to address the limitations of conventional adaptive optics (AO) systems in measuring large-asphericity surfaces. Conventional adaptive optics (AO) which is usually combined with a common path interferometer, is confined to measuring surfaces comparable to the beam spot size (usually 10 mm to 20 mm), and its commonly employed deformable mirror (DM) exhibits limited lateral resolution. By utilizing the LCOS-SLM's high-definition phase modulation capability, the system dynamically modifies diffracted wavefronts to compensate for high-order aspheric aberrations while expanding the lateral measurement range through non-common-path PPDI optics. The proposed method synthesizes aspheric wavefronts via Zernike polynomial-based patterns (specifically utilizing the defocus term, Z4 loaded onto the LCOS-SLM), enabling precise surface profile retrieval through phase-shifting interferometry. Experimental validation on both a parabolic and a 6th-order aspheric mirror demonstrated measurement accuracy with root-mean-square (RMS) deviations below λ/25, confirming the efficacy of LCOS-SLM-driven wavefront compensation. The integration of PPDI and LCOS-SLM eliminates aperture constraints imposed by traditional AO compensators. In principle, as long as the numerical aperture (NA) of the measured surface is smaller than that of the PPDI-generated testing wavefront, the approach is geometrically scalable to larger apertures. Furthermore, LCOS-SLM overcomes the low wavefront modulation resolution inherent in deformable mirrors (DM), and enables high-order aberration-based wavefront modulation through a developed LCOS-SLM pattern generation program. This approach provides a scalable solution for rotationally symmetric aspheric surface metrology in applications such as extreme ultraviolet lithography and precision optical manufacturing.