Handheld Fluorescence Spectrometer Enabling Sensitive Aflatoxin Detection in Maize.

Aflatoxins are among the main carcinogens threatening food and feed safety while imposing major detection challenges to the agrifood industry. Today, aflatoxins are typically detected using destructive and sample-based chemical analysis that are not optimally suited to sense their local presence in the food chain. Therefore, we pursued the development of a non-destructive optical sensing technique based on fluorescence spectroscopy. We present a novel compact fluorescence sensing unit, comprising both ultraviolet excitation and fluorescence detection in a single handheld device. First, the sensing unit was benchmarked against a validated research-grade fluorescence setup and demonstrated high sensitivity by spectrally separating contaminated maize powder samples with aflatoxin concentrations of 6.6 µg/kg and 11.6 µg/kg. Next, we successfully classified a batch of naturally contaminated maize kernels within three subsamples showing a total aflatoxin concentration of 0 µg/kg, 0.6 µg/kg and 1647.8 µg/kg. Consequently, our novel sensing methodology presents good sensitivity and high potential for integration along the food chain, paving the way toward improved food safety.

Wide-Field-of-View Multispectral Camera Design for Continuous Turfgrass Monitoring.

Sustainably using resources, while reducing the use of chemicals, is of major importance in agriculture, including turfgrass monitoring. Today, crop monitoring often uses camera-based drone sensing, offering an accurate evaluation but typically requiring a technical operator. To enable autonomous and continuous monitoring, we propose a novel five-channel multispectral camera design suitable for integrating it inside lighting fixtures and enabling the sensing of a multitude of vegetation indices by covering visible, near-infrared and thermal wavelength bands. To limit the number of cameras, and in contrast to the drone-sensing systems that show a small field of view, a novel wide-field-of-view imaging design is proposed, featuring a field of view exceeding 164°. This paper presents the development of the five-channel wide-field-of-view imaging design, starting from the optimization of the design parameters and moving toward a demonstrator setup and optical characterization. All imaging channels show an excellent image quality, indicated by an MTF exceeding 0.5 at a spatial frequency of 72 lp/mm for the visible and near-infrared imaging designs and 27 lp/mm for the thermal channel. Consequently, we believe our novel five-channel imaging design paves the way toward autonomous crop monitoring while optimizing resource usage.

Freeform Wide Field-of-View Spaceborne Imaging Telescope: From Design to Demonstrator.

Wide field-of-view imaging optics offer a huge potential for space-based Earth observation enabling the capture of global data. Reflective imaging telescopes are often favored, as they do not show chromatic aberrations and are less susceptible to radiation darkening than their refractive counterparts. However, the main drawback of reflective telescopes is that they are limited with respect to field-of-view while featuring large dimensions. We propose the use of freeform optics to maximize the field of view while maintaining diffraction-limited image quality and minimizing system dimensions. In this paper, we present a novel freeform wide field-of-view reflective telescope, starting from the optical design, and continuing to tolerancing analysis and manufacture, towards a proof-of-concept demonstrator. The novel telescope features a full field-of-view of 120° while showing an exceptional spatial resolution of 2.6 km and fitting within 1 CubeSat unit. To the best of our knowledge, this is the widest field-of-view that has ever been realized for a space-based telescope, nearly reaching Earth observation from limb to limb from an altitude of about 700 km. We hope this design paves the way for future space missions enabling improved Earth observation and leading to enhanced monitoring of climate and climate change.

Optical Design of a Novel Wide-Field-of-View Space-Based Spectrometer for Climate Monitoring.

We report on a near-infrared imaging spectrometer for sensing the three most prominent greenhouse gases in the atmosphere (water vapor, carbon dioxide and methane). The optical design of the spectrometer involves freeform optics, which enables achieving exceptional performance and allows progressing well beyond the state-of-the-art in terms of compactness, field-of-view, and spatial resolution. The spectrometer is intended to be launched on a small satellite orbiting at 700 km and observing the Earth with a wide field-of-view of 120° and a spatial resolution of 2.6 km at nadir. The satellite will ultimately allow for improved climate change monitoring.

Miniature freeform flow-line lightguide for sensing: from design to fabrication.

We present the development of a compact (about 1.3 × 2.0 × 20 mm3) freeform optical lightguide for sensing applications, from the conceptual design to the fabrication through injection molding. The design of the optic is based on the flow-line method from Nonimaging Optics, which allows the desired optical functionalities (45° half-acceptance and 40° beam steering) while meeting particularly tight mechanical and geometrical constraints. An extensive analysis of the effects of fabrication parameters on the performances demonstrates the importance of minimizing the fillet radius. This requisite inspired a special procedure for designing the mold, which is built as a "3D puzzle" assembly of separate pieces, each one dedicated to one specific side surface of the lightguide. This technique enables uniform optical quality on all the optic's surfaces and removes the need of a fillet radius in the mold. At present, the first lightguide prototypes have been fabricated; after the coating phase, they will be ready for the validation stage.

Wide-Field-of-View Longwave Camera for the Characterization of the Earth's Outgoing Longwave Radiation.

The measurement of the Earth's Outgoing Longwave Radiation plays a key role in climate change monitoring. This measurement requires a compact wide-field-of-view camera, covering the 8-14 µm wavelength range, which is not commercially available. Therefore, we present a novel thermal wide-field-of-view camera optimized for space applications, featuring a field of view of 140° to image the Earth from limb to limb, while enabling a high spatial resolution of 4.455 km at nadir. Our cost-effective design comprises three germanium lenses, of which only one has a single aspherical surface. It delivers a very good image quality, as shown by the nearly-diffraction-limited performance. Radiative transfer simulations indicate excellent performance of our camera design, enabling an estimate of the broadband Outgoing Longwave Radiation with a random relative error of 4.8%.

Two-channel multiresolution refocusing imaging system using a tunable liquid lens.

Multichannel imaging systems currently feature refocusing capabilities only in bulky and expensive designs. Mechanical movements of the components cannot be integrated in miniaturized designs, preventing classical refocusing mechanisms. To overcome this limitation we developed, as a proof-of-concept (POC) demonstration, a compact low-cost two-channel refocusing imaging system based on a voltage-tunable liquid lens. In addition, the design can be realized with wafer-level manufacturing techniques. One channel of the imaging system enables a wide field of view (FOV) of a scene (2×40°) but with a limited angular resolution (0.078°), while the other channel gives a high angular resolution (0.0098°) image of a small region of interest but with a much narrower FOV (2×7.57°). It is this high-resolution channel that contains the tunable lens and therefore the refocusing capability. A POC demonstration of the proposed two-channel system was built and its performances were measured. Both imaging channels show good overall diffraction-limited image quality.