When the ESA Earth observation mission FLEX launches into space on September 15, 2026, as scheduled, it will carry high-precision optical components from Jena, Germany. Researchers at the Fraunhofer Institute for Applied Optics and Precision Engineering IOF have developed and manufactured a silicon-based doubleslit assembly as well as two high-precision mirrors for the spectrometer on board the satellite. The spectrometer is designed to detect the fluorescence of plants excited by sunlight from Earth’s orbit. The data is expected to provide new insights into the photosynthetic activity, health, and stress levels of vegetation.
The FLEX mission will address the question: How much light do plants emit, and what can this light emission tell us about the health of the plants? At the heart of the satellite will be the “Fluorescence Imaging Spectrometer,” or FLORIS for short. Unlike many other spectrometers, FLORIS does not operate with a single light channel but with two: One channel provides particularly high-resolution information on closely adjacent wavelengths, while the second covers a broader range of the light spectrum. This requires an extremely precise dual-slit assembly.
“The fluorescence signals emitted by plants are very weak. For FLORIS to analyze these signals reliably, the optical components must be manufactured and assembled with exceptional precision,” says Dr. Falk Kemper, project manager for the FLEX project at Fraunhofer IOF. “The double slit enables a combination of high spectral resolution and broad spectral coverage. Its fabrication pushed the limits of what is technically feasible.”