Black phosphorus (BP) has emerged as a promising materials system for mid-wave infrared photodetection because of its moderate bandgap, high carrier mobility, substrate compatibility, and bandgap tunability. However, its uniquely tunable bandgap can only be taken advantage of with thin layer thicknesses, which ultimately limits the optical absorption of a BP photodetector. This work demonstrates an absorption-boosting resonant metal−insulator−metal (MIM) metasurface grating integrated with a thin-film BP photodetector. We designed and fabricated different MIM gratings and characterized their spectral properties. Then, we show that an MIM structure increased room temperature responsivity from 12 to 77 mA W −1 at 3.37 μm when integrated with a thin-film BP photodetector. Our results show that MIM structures simultaneously increase mid-wave infrared absorption and responsivity in a thin-film BP photodetector.

BackgroundRemote monitoring of plants using hyperspectral imaging has become an important tool for the study of plant growth, development, and physiology. Many applications are oriented towards use in field environments to enable non-destructive analysis of crop responses due to factors such as drought, nutrient deficiency, and disease, e.g., using tram, drone, or airplane mounted instruments. The field setting introduces a wide range of uncontrolled environmental variables that make validation and interpretation of spectral responses challenging, and as such lab- and greenhouse-deployed systems for plant studies and phenotyping are of increasing interest. In this study, we have designed and developed an open-source, hyperspectral reflectance-based imaging system for lab-based plant experiments: the HyperScanner. The reliability and accuracy of HyperScanner were validated using drought and salt stress experiments with Arabidopsis thaliana.ResultsA robust, scalable, and reliable system was created. The system was built using open-sourced parts, and all custom parts, operational methods, and data have been made publicly available in order to maintain the open-source aim of HyperScanner. The gathered reflectance images showed changes in narrowband red and infrared reflectance spectra for each of the stress tests that was evident prior to other visual physiological responses and exhibited congruence with measurements using full-range contact spectrometers.ConclusionsHyperScanner offers the potential for reliable and inexpensive laboratory hyperspectral imaging systems. HyperScanner was able to quickly collect accurate reflectance curves on a variety of plant stress experiments. The resulting images showed spectral differences in plants shortly after application of a treatment but before visual manifestation. HyperScanner increases the capacity for spectroscopic and imaging-based analytical tools by providing more access to hyperspectral analyses in the laboratory setting.Electronic supplementary materialThe online version of this article (10.1186/s13007-019-0392-1) contains supplementary material, which is available to authorized users.

The Breakthrough Starshot Initiative, established in 2016, aims to propel an ultra-lightweight spacecraft to Alpha Centauri using radiation pressure from a high-power, ground-based laser. Nanopatterned silicon nitride has been proposed as a candidate material for the laser sail. In this work, we design and fabricate a silicon nitride photonic crystal with high reflectivity around a laser wavelength of 1064 nm. We demonstrate the ability to shift the resonant features of the laser sail using titanium dioxide coatings and increase the longwave infrared emissivity using polymer coatings. We also characterize the response of the sail to temperature and optical power.

The ability to tailor light–matter interactions using artificially engineered materials has opened up new avenues for secure data storage and communication. This work presents an experimental investigation of metasurfaces for secure, multi‐channel image encryption in the infrared (IR). The proposed metasurfaces consist of an array of pixels, each designed to produce a wavelength‐ and polarization‐dependent IR absorptivity. A basis set of pixels is designed for encrypting images of arbitrary resolution on a given number of wavelength and polarization channels. These pixels are fabricated, and their spectral response is experimentally measured using Fourier transform infrared spectroscopy. The measured data is used to emulate the encryption and decryption of binary and 8‐bit grayscale images. Finally, the security of the encryption scheme proposed in this work is evaluated by performing statistical analyses on the image data stored on different channels. The results presented in this study suggest intriguing possibilities for the development of encrypted tagging technologies in the infrared and thus have implications for secure object identification and anti‐counterfeiting.

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