![]() ![]() The hyperboloidal phase distribution metalens can realise diffraction-limited focusing 26, 27. The phase distribution regulated by a metalens determines its function. In general, three main methods have been applied to manipulate the phase distribution of metalenses, including use of the propagation phase 11, 12, resonance phase 13, 14, 15, 16, 17 and geometric phase 18, 19, 20, 21, 22, 23, 24, 25. On-demand phase manipulation is one of the essential abilities of a metalens 9, 10. Metalenses, as emergent metasurfaces 1, 2, 3, 4, 5, 6, 7, 8, have attracted increasing interest for their possible applications in advanced imaging and focusing. Our phase measurement system will help not only designers optimise the designs of metalenses but also fabricants distinguish defects to improve the fabrication process, which will pave the way for metalenses in industrial applications. We also use the measured phase distribution to quantitatively characterise the imaging performance of the metalens. Furthermore, through phase distribution analysis, it is found that the distance between the measured metalens and the brightest spot of focusing will deviate from the focal length when the metalens has a low nominal numerical aperture, even though the metalens is ideal without any fabrication error. ![]() ![]() Different sensitivities of the phase response to wavelength between the Pancharatnam-Berry phase-based metalens and propagation phase-reliant metalens are directly observed in the experiment. Based on the measured phase distribution, we analyse the negative chromatic aberration effect of monochromatic metalenses and propose a feature size of metalenses. We have developed an interferometric imaging phase measurement system to measure the phase distribution of a metalens by taking only one photo of the interference pattern. However, the phase distribution of a metalens has not been measured directly up to now, hindering further quantitative evaluation of its performance. Metalenses have emerged as a new optical element or system in recent years, showing superior performance and abundant applications. ![]()
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