Design and experimental validation of a modified Dyson imaging spectrometer for solar-induced chlorophyll fluorescence detection.

Solar-induced chlorophyll fluorescence (SIF) imaging requires spectrometers with high spectral resolution, high throughput, and compact optical layouts. We present a modified Dyson imaging spectrometer for SIF detection, in which a lens-grating combination replaces the conventional concave grating to increase the slit-to-detector distance and improve linear spectral dispersion. The optimized system achieves a spectral resolution better than 0.3 nm, RMS spot radii below 7 µm across the full field of view, smile distortion below 1.4 µm, and keystone less than 2.75 µm. A prototype spectrometer was fabricated and calibrated. Measurements with an Hg-Ar lamp show a spectral full width at half maximum of 0.274-0.297 nm, and laboratory tests demonstrate a signal-to-noise ratio above 200 within the working band. Outdoor hyperspectral imaging experiments further verify the instrument performance, and SIF images of vegetation were retrieved at 762 nm using the 3FLD method. These results demonstrate that the proposed spectrometer provides an effective solution for high-resolution SIF imaging.