A prototype OFS has been developed for space application and has been fully described by Daybell et al. A schematic diagram of the rare gas cell, electron lens, and photoelectric energy analyzer is shown in Figure 5. This instrument has no degradable optical elements, a problem common to conventional optical spectrometers, and it also eliminates the problem of multiple order separation. The OFS technique has been successfully demonstrated on rocket flight 36.131U S, and is presently being enhanced. A schematic view of the OFS is shown in Figure 4.
Photons enter from the right through a collimator filled with the rare gas of interest.
Behind the gas box on the left is a light trap. One enhancement not shown in the schematic, but already implemented, is the magnetic shielding required to screen out the Earth's field. The absence of such shielding is known to restrict the wavelength region of the OFS operation to wavelengths shortwar d of 400 . The flow of target gas out of the gas box region is constrained by the aperture and collimator along the incoming photon beam, and by the small slit on the bottom of the gas box connecting it with the electron lens. The five element electron lens allows a reduction of escaping target gas in the path of the electrons being analyzed.