Perspectives and recent advances in super-resolution spectroscopy: Stochastic and disordered-based approaches

Spectroscopic applications are characterized by the constant effort to combine high spectral resolution with large bandwidth. A trade-off typically exists between these two aspects, but the recent development of super-resolved spectroscopy techniques is bringing new opportunities into this field. This is particularly relevant for all applications where compact and cost-effective instruments are needed such as in sensing, quality control, environmental monitoring, or biometric authentication, to name a few. These unconventional approaches exploit several strategies for spectral investigation, taking advantage of concepts such as sparse sampling, artificial intelligence, or post-processing reconstruction algorithms. In this Perspective, we discuss the main strengths and weaknesses of these methods, tracing promising future directions for their further development and widespread adoption. Published under an exclusive license by AIP Publishing

Finite-Size and Illumination Conditions Effects in All-Dielectric Metasurfaces

Dielectric metasurfaces have emerged as a promising alternative to their plasmonic counterparts due to lower ohmic losses, which hinder sensing applications and nonlinear frequency conversion, and their larger flexibility to shape the emission pattern in the visible regime. To date, the computational cost of full-wave numerical simulations has forced the exploitation of the Floquet theorem, which implies infinitely periodic structures, in designing such devices. In this work, we show the potential pitfalls of this approach when considering finite-size metasurfaces and beam-like illumination conditions, in contrast to the typical infinite plane-wave illumination compatible with the Floquet theorem

Robust radiative cooling via surface phonon coupling-enhanced emissivity from SiO2 micropillar arrays

Silicon dioxide (SiO2) is a prominent candidate for radiative cooling applications due to its low absorption in solar wavelengths (0.25-2.5 µm) and exceptional stability. However, its bulk phonon-polariton band results in a strong reflection peak in the atmospheric transparency window (8-13 µm), making it difficult to meet the requirements for sub-ambient passive radiative cooling. Herein, we demonstrate that SiO2 micropillar arrays can effectively suppress infrared reflection at 8-13 µm and enhance the infrared emissivity by optimizing the micropillar array structure. We created a pattern with a height, spacing, and diameter of approximately 1.45 µm, 0.15 µm, and 0.35 µm, respectively, on top of a bulk SiO2 substrate using reactive ion etching. The resulting surface phonon coupling of the micropillar array led to an increase in the thermal emissivity from 0.79 to 0.94. Outdoor tests show that the SiO2 cooler with an optimized micropillar array can generate an average temperature drop of 5.5 °C throughout the daytime underneath an irradiance of 843.1 W/m^2 at noon. Furthermore, the micropillar arrays endow the SiO2 cooler with remarkable hydrophobic properties, attributed to the formation of F/C compounds introduced during the etching process. Finally, we also replicated the micropillar pattern onto the surface of industrial optical solar reflectors (OSRs), demonstrating similar emissivity and hydrophobicity enhancements. Our findings revealed an effective strategy for modifying the thermal management features of durable SiO2 layers, which can be harnessed to cool OSRs and other similar sky-facing devices

Designer SiO2 Metasurfaces for Efficient Passive Radiative Cooling

In recent years, an increasing number of passive radiative cooling materials are proposed in the literature, with several examples relying on the use of silica (SiO2) due to its unique stability, non-toxicity, and availability. Nonetheless, due to its bulk phonon-polariton band, SiO2 presents a marked reflection peak within the atmospheric transparency window (8-13 mu m), leading to an emissivity decrease that poses a challenge to fulfilling the criteria for sub-ambient passive radiative cooling. Thus, the latest developments in this field are devoted to the design of engineered SiO2 photonic structures, to increase the cooling potential of bulk SiO2 radiative coolers. This review seeks to identify the most effective photonic design and fabrication strategies for SiO2 radiative emitters by evaluating their cooling efficacy, as well as their scalability, providing an in-depth analysis of the fundamental principles, structural models, and results (both numerical and experimental) of various types of SiO2 radiative coolers

Recent progress in organic-based radiative cooling materials: fabrication methods and thermal management properties

Organic-based materials capable of radiative cooling have attracted widespread interest in recent years due to their ease of engineering and good adaptability to different application scenarios. As a cooling material for walls, clothing, and electronic devices, these materials can reduce the energy consumption load of air conditioning, improve thermal comfort, and reduce carbon emissions. In this paper, an overview is given of the current fabrication strategies of organic-based radiative cooling materials, and of their properties. The methods and joint thermal management strategies including evaporative cooling, phase-change materials, fluorescence, and light-absorbing materials that have been demonstrated in conjunction with a radiative cooling function are also discussed. This review provides a comprehensive overview of organic-based radiative cooling, exemplifying the emerging application directions in this field and highlighting promising future research directions in the field

Machine-Learning-Assisted Design of a Robust Biomimetic Radiative Cooling Metamaterial

Recently, biomimetic photonic structural materials have significantly improved their radiative cooling performance. However, most research has focused on understanding cooling mechanisms, with limited exploration of sensitive parameter variations. Traditional numerical methods are costly and time-consuming and often struggle to identify optimal solutions, limiting the scope of high-performance microstructure design. To address these challenges, we integrated machine learning into the design of Batocera LineolataHope bionic photonic structures, using SiO2 as the substrate. Deep learning models provided insights into the complex relationship between bionic metamaterials and their spectral response, enabling us to identify the optimal performance parameter range for truncated cone arrays (height-to-diameter ratio (H/D-bottom) from 0.8 to 2.4), achieving a high average emissivity of 0.985. Experimentally, the noon temperature of fabricated samples decreased by about 8.3 degrees C. This data-driven approach accelerates the design and optimization of robust biomimetic radiative cooling metamaterials, promising significant advancements in standardized passive radiative cooling applications

Bright-white beetle scales optimise multiple scattering of light

This is the final version of the article. Available from the publisher via the DOI in this record.Error in funder statement in this article is corrected in http://hdl.handle.net/10871/22212Whiteness arises from diffuse and broadband reflection of light typically achieved through optical scattering in randomly structured media. In contrast to structural colour due to coherent scattering, white appearance generally requires a relatively thick system comprising randomly positioned high refractive-index scattering centres. Here, we show that the exceptionally bright white appearance of Cyphochilus and Lepidiota stigma beetles arises from a remarkably optimised anisotropy of intra-scale chitin networks, which act as a dense scattering media. Using time-resolved measurements, we show that light propagating in the scales of the beetles undergoes pronounced multiple scattering that is associated with the lowest transport mean free path reported to date for low-refractive-index systems. Our light transport investigation unveil high level of optimisation that achieves high-brightness white in a thin low-mass-per-unit-area anisotropic disordered nanostructure.We wish to thank R. Blumenfeld, T. Svensson, R. Savo and K. Vynck for fruitful discussions, B.D. Wilts for the comments on the manuscript and J. Aizenberg for support in the SEM measurements. The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement n [291349] and USAF grant FA9550-10-1-002

ERRATUM: Bright-white beetle scales optimise multiple scattering of light.

Original article available via doi:10.1038/srep06075Erratum: Scientific Reports 4, Article number: 6075 (2014); Published: 15 August 2014; Updated: 19 December 2014 doi:10.1038/srep06075. This Article contains an error in the Acknowledgements section

Metrological framework for passive radiative cooling technologies and development setups for reproducible in-field performance testing

Almost 20 % of the global electricity consumption is caused by cooling systems. As the demand for cooling is expected to grow tenfold by 2050, improving the efficiency of cooling systems plays a critical role in addressing the global climate challenge. Passive Radiative Cooling (PRC) materials, which can dissipate heat into the surrounding as thermal radiation (especially through the atmospheric infrared window between 8 µm and 13 µm) have recently emerged. Hence, the project PaRaMetriC (Metrological Framework for Passive Radiative Cooling Technologies) aims to develop a comprehensive metrological framework with standardized performance indicators and testing protocols to enable comparable evaluation of their cooling performance on-site and the determination of potential energy savings that could derive from the deployment of such technologies. One work package within this project deals with the design of a testing setup and the development of a protocol for determining the figures of merit of candidate PRC materials by in-field measurements with a relative uncertainty below 10 %. For this purpose, on-site prototype setups are planned to be realized in different climatic regions, e.g. Barcelona (maritime Mediterranean climate), Madrid (continental Mediterranean climate), Torino (warm temperate climate) and Würzburg (moderate temperate climate), in order to cover a wide range of environmental conditions. With these prototype setups, measurements will be performed on candidate benchmark materials. Additionally, the environmental and atmospheric conditions (temperature, solar irradiance, humidity, wind speed, etc.) will be monitored during the measurements using appropriate sensors. Up to now, the design work has been started. This presentation gives an overview of the PaRaMetriC project and provides an outlook on the aimed future activities regarding the setup for in-field measurements, including the configuration of the setup (thermal insulation, thermal load, etc.), the selection of appropriate sensors and the implementation of PRC materials. Furthermore, previous work will be presented. So far, first PRC materials with high solar reflectance and high thermal emittance have been prepared. Beside the infrared-optical properties, the thermal conductivity of the prepared layers has also been measured. At these samples, the derived surface temperature has been measured for sky-facing surfaces in dependence on the surrounding conditions. Together with measurements on reference materials, the correlation of the surface temperature with the solar reflectance index (SRI) has been investigated. The SRI value has been determined by measurements of the solar reflectance and thermal emittance of the prepared PRC materials according to ASTM E 1980 - 11. As a preliminary result, a temperature drop below ambient air temperature has been recorded for some prepared PRC materials even during the day in sunshine

Usefulness of bronchoalveolar lavage in suspect COVID-19 repeatedly negative swab test and interstitial lung disease

The diagnosis of coronavirus disease 2019 (COVID-19) relies on nasopharyngeal swab, which shows a 20–30% risk of false negativity [1]. Bronchoalveolar lavage (BAL) is reported to be useful in patients with pulmonary interstitial infiltrates on high-resolution computed tomography (HRCT). We investigated the usefulness of BAL in symptomatic patients with positive HRCT and a repeatedly negative swab test (‘grey zone’)