The lazy way to keep cool in the sun: Passive radiative cooling requires a material that radiates heat away while allowing solar radiation to pass through. Zhai et al. solve this riddle by constructing a metamaterial composed of a polymer layer embedded with microspheres, backed with a thin layer of silver (see the Perspective by Zhang). The result is an easy-to-manufacture material near the theoretical limit for daytime radiative cooling. The translucent and flexible film can be made in large quantities for a variety of energy technology applications. Science , this issue p. 1062 ; see also p. 1023

A durable way to keep cool: The fibers that make up textiles can be augmented to change how they interact with thermal radiation, but the resulting materials often are not durable. Zeng et al . developed a multilayer metafabric composed of a titanium oxide polylactic acid composite laminated with a polytetrafluoroethylene layer. This combination creates a textile that has passive radiative cooling properties with good mechanical properties and scalability. The textile can be made into clothes or car covers and keeps a person or a car much cooler than other fabrics. —BG

Both Raman spectroscopy and the photoluminescence (PL) spectroscopy are intensively used in studying the characteristics of monolayer MoS₂. However, the substrate-related interference effect will influence the optical signal intensities collected from monolayer MoS₂. In this work, we investigated the influence of multilayer film interference on the optical signal intensity of monolayer MoS₂ on SiO₂/Si substrate. Based on our results, the most commonly used substrate for monolayer MoS₂, SiO₂/Si with SiO₂ thickness around 280–300 nm, is not the optimized choice. By considering the interference effect caused by the Air-MoS₂-SiO₂ multilayers, we can now enhance the optical signal intensity of monolayer MoS₂ greatly by selecting proper SiO₂ thickness for any chosen incident light wavelength.

The wide application of optical spectroscopy makes miniaturized spectrometers with fundamental importance. The scalability, high-performance, low-cost, and small footprint are still contradicting each other and limiting the applicability of miniaturized spectrometer for practical application. Here we propose a compact spectrometer that satisfies the four advantages. The device uses a fiber taper tip to generate complex leaky mode patterns within 1 mm length. The unique correspondence between the pattern and wavelength operates effectively for hundreds of nanometers spectral range while providing a spectral resolution around ~ 1 pm. The integration of multiple taper tips enables hyperspectral imaging applications. The working range of our device can be further extended using different materials and detectors while keeping the similar architecture.

The periodic extension of phase difference is commonly applied in device design to obtain phase compensation beyond the system’s original phase modulation capabilities. Based on this extension approach, we propose the application of quasiphase delay matching to extend the range of dispersion compensation for meta-atoms with limited height. Our theory expands the limit of frequency bandwidth coverage and relaxes the constraints of aperture, NA, and bandwidth for metalenses. By applying the uncertainty principle, we explain the fundamental limit of this achromatic bandwidth and obtain the achromatic spectrum using perturbation analysis. To demonstrate the effectiveness of this extended limit, we simulate a quasiachromatic metalens with a diameter of 2 mm and a NA of 0.55 in the range of 400–1500 nm. Our findings provide a novel theory for correcting chromatic aberration in large-diameter ultrawide bandwidth devices.