Design strategies for efficient, fabrication-feasible extreme-ultraviolet metalens

TL;DR

This paper introduces new design strategies for EUV metalenses that significantly improve focusing efficiency by optimizing layout schemes and metaatom mapping, overcoming material and fabrication limitations.

Contribution

It proposes alternative design strategies and semi-analytical approaches that roughly double EUV metalens efficiency without reducing feature size.

Findings

Focusing efficiency can be roughly doubled using the proposed design strategies.

Alternative layout schemes outperform simple square-lattice designs.

Strategies are applicable to metaoptics with lossy metaatoms or diffraction issues.

Abstract

The concept of metasurfaces was recently applied to the extreme ultraviolet (EUV) spectral regime, providing a new opportunity for transmissive focusing elements in a regime where materials are highly lossy. The realization of metalenses in the EUV, however, is challenging due to the optical losses and low refractive index contrast of available materials, as well as the larger-than-wavelength periodicity of metaatom arrays imposed by fabrication limits. In this paper, we propose alternative EUV metalens design strategies, including layout schemes and metaatom mapping rules. We demonstrate that the focusing efficiency can be roughly doubled compared with the simple square-lattice design of an EUV metalens purely by using an alternative semi-analytical design approach without reducing the metasurface's minimum feature size. The proposed strategies are generally applicable to metaoptics design for efficiency improvement when metaatoms are lossy or induce diffraction orders.