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1. Microscopy is better in color: development of a streamlined spectral light path for real-time multiplex fluorescence microscopy

   https://doi.org/10.1364/BOE.453657  

   Browning, Craig M. ; Mayes, Samantha ; Mayes, Samuel A. ; Rich, Thomas C. ; Leavesley, Silas J. ( June 2022 , Biomedical Optics Express)

   Spectroscopic image data has provided molecular discrimination for numerous fields including: remote sensing, food safety and biomedical imaging. Despite the various technologies for acquiring spectral data, there remains a trade-off when acquiring data. Typically, spectral imaging either requires long acquisition times to collect an image stack with high spectral specificity or acquisition times are shortened at the expense of fewer spectral bands or reduced spatial sampling. Hence, new spectral imaging microscope platforms are needed to help mitigate these limitations. Fluorescence excitation-scanning spectral imaging is one such new technology, which allows more of the emitted signal to be detected than comparable emission-scanning spectral imaging systems. Here, we have developed a new optical geometry that provides spectral illumination for use in excitation-scanning spectral imaging microscope systems. This was accomplished using a wavelength-specific LED array to acquire spectral image data. Feasibility of the LED-based spectral illuminator was evaluated through simulation and benchtop testing and assessment of imaging performance when integrated with a widefield fluorescence microscope. Ray tracing simulations (TracePro) were used to determine optimal optical component selection and geometry. Spectral imaging feasibility was evaluated using a series of 6-label fluorescent slides. The LED-based system response was compared to a previously tested thin-film tunable filter (TFTF)-based system. Spectral unmixing successfully discriminated all fluorescent components in spectral image data acquired from both the LED and TFTF systems. Therefore, the LED-based spectral illuminator provided spectral image data sets with comparable information content so as to allow identification of each fluorescent component. These results provide proof-of-principle demonstration of the ability to combine output from many discrete wavelength LED sources using a double-mirror (Cassegrain style) optical configuration that can be further modified to allow for high speed, video-rate spectral image acquisition. Real-time spectral fluorescence microscopy would allow monitoring of rapid cell signaling processes (i.e., Ca²⁺and other second messenger signaling) and has potential to be translated to clinical imaging platforms.

    

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2. Ultraviolet and Near‐Infrared Dual‐Band Selective‐Harvesting Transparent Luminescent Solar Concentrators

   https://doi.org/10.1002/aenm.202003581  

   Yang, Chenchen ; Sheng, Wei ; Moemeni, Mehdi ; Bates, Matthew ; Herrera, Christopher K. ; Borhan, Babak ; Lunt, Richard R. ( February 2021 , Advanced Energy Materials)

   Visibly transparent luminescent solar concentrators (TLSC) can optimize both power production and visible transparency by selectively harvesting the invisible portion of the solar spectrum. Since the primary applications of TLSCs include building envelopes, greenhouses, automobiles, signage, and mobile electronics, maintaining aesthetics and functionalities is as important as achieving high power conversion efficiencies (PCEs) in practical deployment. In this work, massive‐downshifting phosphorescent nanoclusters and fluorescent organic molecules are combined into a TLSC system as ultraviolet (UV) and near‐infrared (NIR) selective‐harvesting luminophores, respectively, demonstrating UV and NIR dual‐band selective‐harvesting TLSCs with PCE over 3%, average visible transmittance (AVT) exceeding 75% and color metrics suitable for the window industry. With distinct wavelength‐selectivity and effective utilization of the invisible portion of the solar spectrum, this work reports the highest light utilization efficiency (PCE × AVT) of 2.6 for a TLSC system, the highest PCE of any transparent photovoltaic (TPV) devices with AVT greater than 70%, and outperforms the practical limit for non‐wavelength‐selective TPV.

    

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3. High-Resolution Snow-Covered Area Mapping in Forested Mountain Ecosystems Using PlanetScope Imagery

   https://doi.org/10.3390/rs14143409  

   John, Aji ; Cannistra, Anthony F. ; Yang, Kehan ; Tan, Amanda ; Shean, David ; Hille Ris Lambers, Janneke ; Cristea, Nicoleta ( July 2022 , Remote Sensing)

   Improving high-resolution (meter-scale) mapping of snow-covered areas in complex and forested terrains is critical to understanding the responses of species and water systems to climate change. Commercial high-resolution imagery from Planet Labs, Inc. (Planet, San Francisco, CA, USA) can be used in environmental science, as it has both high spatial (0.7–3.0 m) and temporal (1–2 day) resolution. Deriving snow-covered areas from Planet imagery using traditional radiometric techniques have limitations due to the lack of a shortwave infrared band that is needed to fully exploit the difference in reflectance to discriminate between snow and clouds. However, recent work demonstrated that snow cover area (SCA) can be successfully mapped using only the PlanetScope 4-band (Red, Green, Blue and NIR) reflectance products and a machine learning (ML) approach based on convolutional neural networks (CNN). To evaluate how additional features improve the existing model performance, we: (1) build on previous work to augment a CNN model with additional input data including vegetation metrics (Normalized Difference Vegetation Index) and DEM-derived metrics (elevation, slope and aspect) to improve SCA mapping in forested and open terrain, (2) evaluate the model performance at two geographically diverse sites (Gunnison, Colorado, USA and Engadin, Switzerland), and (3) evaluate the model performance over different land-cover types. The best augmented model used the Normalized Difference Vegetation Index (NDVI) along with visible (red, green, and blue) and NIR bands, with an F-score of 0.89 (Gunnison) and 0.93 (Engadin) and was found to be 4% and 2% better than when using canopy height- and terrain-derived measures at Gunnison, respectively. The NDVI-based model improves not only upon the original band-only model’s ability to detect snow in forests, but also across other various land-cover types (gaps and canopy edges). We examined the model’s performance in forested areas using three forest canopy quantification metrics and found that augmented models can better identify snow in canopy edges and open areas but still underpredict snow cover under forest canopies. While the new features improve model performance over band-only options, the models still have challenges identifying the snow under trees in dense forests, with performance varying as a function of the geographic area. The improved high-resolution snow maps in forested environments can support studies involving climate change effects on mountain ecosystems and evaluations of hydrological impacts in snow-dominated river basins. 

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4. Ultra-fast Thermoreflectance Imaging for Electronic, Optoelectronic, and Thermal Devices

   https://doi.org/10.1109/BCICTS45179.2019.8972732  

   Bahk, Je-Hyeong ; Shakouri, Ali ( January 2020 , 2019 IEEE BiCMOS and Compound semiconductor Integrated Circuits and Technology Symposium (BCICTS))

   We review the recent advances in thermal characterization of micro/nanoscale electronic, optoelectronic, thermal devices based on thermoreflectance imaging. Thermoreflectance imaging is a non-invasive optical technique that can visualize surface thermal response of devices and integrated circuits (IC). Recent advances of the technique have enabled high-resolution, ultra-fast transient thermal imaging with 800 ps temporal resolution. Using visible or UV illumination, spatial resolution of about 200-250 nm can be achieved. Many IC substrates, e.g. Si, GaAs, are transparent to near IR illumination in 1-1.5 μm wavelength range. Through-substrate thermal imaging of flip-chip bonded ICs with micron spatial resolution has been demonstrated. We provide key examples of various devices characterized by the technique such as CMOS ICs, GaN HEMT, nanowire transistors, thin-film solar cells, and micro-thermal cloaking devices. In addition to the validation of electrothermal models, material and fabrication defects can be identified. Finally we discuss the advantages/limitations, and perspective of thermoreflectance imaging technique. 

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5. Lower Energy Excitation of Water Soluble Near‐Infrared Emitting Mixed‐Ligand Metallacrowns

   https://doi.org/10.1002/chem.202300226  

   Nguyen, Tu N. ; Eliseeva, Svetlana V. ; Martinić, Ivana ; Carver, Peggy L. ; Lathion, Timothée ; Petoud, Stéphane ; Pecoraro, Vincent L. ( April 2023 , Chemistry – A European Journal)

   By combining advantages of two series of lanthanide(III)/zinc(II) metallacrowns (MCs) assembled using pyrazine‐ (pyzHA²⁻) and quinoxaline‐ (quinoHA²⁻) hydroximate building blocks ligands, we created here water‐soluble mixed‐ligand MCs with extended absorption to the visible range. The Yb^IIIanalogue demonstrated improved photophysical properties in the near‐infrared (NIR) range in cell culture media, facilitating its application for NIR optical imaging in living HeLa cells.

    

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