"Solar spectrometers." . . "Rare gases." . . . . "Extreme ultraviolet radiation." . . . . . . . . . . . "A rare gas optics-free absolute photon flux and energy analyzer for solar and planetary observations final report"@en . . . . . . . . "Rare gas optics free absolute photon"@en . . . "Photoelectric effect." . . "Ultraviolet spectrometers." . . "Solar spectrometry." . .