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Schematic of RFS-OPT setup. O – 4× objective lens, AP – aperture, TL – 200 mm focal length tube lens, R1 – 100 mm focal length relay lens, OL – −100 mm focal length offset lens, ETL – electrically tunable lens, R2 – 100 mm focal length relay lens, EF –emission filter, ϕ – sample diameter.
