High-efficiency reflective focusing in extreme ultraviolet with multilayer metalens.

Extreme ultraviolet metalenses, capable of near-diffraction-limit focusing with spherical minimal aberration, offer significant opportunities for advancing metaoptics and demonstrate transformative potential in applications such as high-precision lithography, high-resolution imaging, and fine measurement. However, in addition to the inevitable material absorption, the current transmissive extreme ultraviolet metalens suffers from low efficiency due to an incomplete 2π phase profile and high-order diffraction. Here, we propose a high-efficiency extreme ultraviolet reflective metalens, composed of multilayer films and vacuum holes. The reflective configurations based on multilayer films support a complete 2π phase profile in a small period with high-efficiency meta-atoms. By reducing the unit period and incorporating multilayer films to suppress high-order diffraction, the reflective metalens with a numerical aperture of 0.05 achieves a high-quality focusing profile with an absolute focusing efficiency of 15.80%, more than double that of previously reported works. Furthermore, the designed structure reaches a maximum NA of nearly 0.3 while ensuring sufficient efficiency, making it comparable to commercial extreme ultraviolet lithography systems. The investigation of wavelength dependence on performance further reinforces the superiority of our design. This work presents a high-efficiency extreme ultraviolet reflective metalens and elucidates its underlying physical mechanisms, paving the way for advanced extreme ultraviolet light manipulation.