Resonant Laser Printing of Optical Metasurfaces.

One of the challenges for metasurface research is upscaling. The conventional methods for fabrication of metasurfaces, such as electron-beam or focused ion beam lithography, are not scalable. The use of ultraviolet steppers or nanoimprinting still requires large-size masks or stamps, which are costly and challenging in further handling. This work demonstrates a cost-effective and lithography-free method for printing optical metasurfaces. It is based on resonant absorption of laser light in an optical cavity formed by a multilayer structure of ultrathin metal and dielectric coatings. A nearly perfect light absorption is obtained via interferometric control of absorption and operating around a critical coupling condition. Controlled by the laser power, the surface undergoes a structural transition from random, semiperiodic, and periodic to amorphous patterns with nanoscale precision. The reliability, upscaling, and subwavelength resolution of this approach are demonstrated by realizing metasurfaces for structural colors, optical holograms, and diffractive optical elements.

How good is your metalens? Experimental verification of metalens performance criterion.

A metric for evaluation of overall metalens performance is presented. It is applied to determination of optimal operating spectral range of a metalens, both theoretically and experimentally. This metric is quite general and can be applied to the design and evaluation of future metalenses, particularly achromatic metalenses.

Optimizing the spectral range of diffractive metalenses for polychromatic imaging applications.

Recent progress has made matalenses a reality, with many publications relating to methods of implementation and performance evaluation of these elements. Basic metalens function is similar to that of a continuous (kinoform) diffractive lens, but the advantage is that they can be manufactured as a binary component. A significant limitation of metalenses, is its strong chromatic aberration. Recently there has been some success in correcting metalens chromatic aberration, albeit at the expense of transmission efficiency towards the desired diffraction order. Clearly, there is a tradeoff between parameters such as spectral bandwidth and spatial resolution. Hence, a major goal of this paper is to set up a metric for evaluation of metalens performance, allowing fair comparison of novel metalens technologies, such as achromatic metalenses, in terms of optical performance. Furthermore, we explore possibilities for practical use of non-chromatically corrected metalenses in polychromatic applications, by optimizing the metalens parameters. It is our hope that the current manuscript will serve as a guide for the design and evaluation of metalenses for practical applications.

Spectrally Gated Microscopy (SGM) with Meta Optics for Parallel Three-Dimensional Imaging.

Volumetric imaging with high spatiotemporal resolution is of utmost importance for various applications ranging from aerospace and defense to real-time imaging of dynamic biological processes. To facilitate three-dimensional sectioning, current technology relies on mechanisms to reject light from adjacent out-of-focus planes either spatially or by other means. Yet, the combination of rapid acquisition time and high axial resolution is still elusive, motivating a persistent pursuit for emerging imaging approaches. Here we introduce and experimentally demonstrate a concept named spectrally gated microscopy (SGM), which enables a single-shot interrogation over the full axial dimension while maintaining a submicron sectioning resolution. SGM utilizes two important features enabled by flat optics (i.e., metalenses or diffractive lenses), namely, a short focal length and strong chromatic aberrations. Using SGM we demonstrate three-dimensional imaging of millimeter-scale samples while scanning only the lateral dimension, presenting a significant advantage over state-of-the-art technology.