Phase characterization of a 0.8-NA metalens via spherical wave reference holography

The phase characterization of large-diameter, high-NA metalenses is fundamentally constrained by the space–bandwidth product (SBP) of imaging-based interferometric systems. Conventional off-axis holography with a plane reference wave struggles because the steep phase gradients of high-NA metalenses broaden the object spectrum in the spatial-frequency domain ( k -space), leading to spectral overlap and aliasing. Here, we introduce spherical wave reference holography (SWRH), which utilizes an engineered spherical reference wave to partially compensate for the metalens phase, thereby significantly reducing the residual phase gradient. This engineered reference compresses the dominant spectral extent of the signal term and substantially relaxes the practical filtering constraint of off-axis holography. We experimentally apply SWRH to a metalens designed for NA =0.8 and achieve reliable phase retrieval over an effective aperture corresponding to D eff ≈460 μm and NA eff ≈0.775. Notably, the retrieved phase maps reveal pronounced phase moiré in high-gradient regions, and propagation analysis further shows that these deterministic phase modulations generate parasitic line-like focal features. These findings establish SWRH as a practical, single-shot method for high-NA metalens phase metrology, as well as a sensitive tool for discretization-induced phase artifacts.