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A normal incidence spectrometer for use in the wavelength region from 200 Å to 1270 Å has been developed. The design and calibration of the instrument are described in detail. The spectrometer can be employed to detect extreme uv radiation at a minimum flux level of 1 rayleigh with a spectral resolution of 40 Å and a spatial resolution of 6°. Data on the extreme uv night sky spectrum between 780 Å and 1270 Å obtained with this instrument on a recent rocket flight are presented.

The class of grazing incidence spectrometers proposed by Cash [ Appl. Opt.21, 710 ( 1982)] and by McClintock Cash [ Proc. Soc. Photo-Opt. Instrum. Eng.331, 12 ( 1982)] for use in the extreme and far ultraviolet has been analyzed. We calculate efficiencies which are lower by a factor of 4 than those estimated by the above authors. This discrepancy is due dominantly to their use of incorrect reflectances. We also calculate a factor of 10 smaller bandpass (3%) and a factor of 2 lower spectral resolution (λ/Δλ ≃ 4000) at the spectrum edges. These discrepancies are due to underestimated camera mirror aberrations and neglect of echelle ripple considerations. We consider modifications to overcome these limitations. A WolterSchwarzschild type-I camera mirror of large radius increases the bandpass by a factor of 10. However, the proposed spectral resolution over this bandpass requires a very long instrument and/or a significant further decrease in efficiency. A sample design consists of a normal incidence camera and a grazing incidence 0.5-sec of arc collecting mirror and delivers λ/Δλ = 20,000 over a 40% range in wavelength. However, the normal incidence reflection decreases the efficiency by an additional factor of 3, only wavelengths longward of ~400 Å are directly accessible, and the total instrument length is 6.7 m. Such limitations preclude the usefulness of this design class in several applications currently under study in astronomical space instrumentation. Other classes of grazing incidence spectrometers which are not subject to these limitations are being investigated.

We have developed a modified Penning discharge lamp for use in the soft x-ray and extreme uv spectral regions. The source produces a number of intense lines in the 50–300-Å range and can be operated for substantial periods of time at high output levels before refurbishment is required. Refurbishment of this source, when required, is very easily effected.

The design and calculated performance is described for a spectrometer included on the Extreme Ultraviolet Explorer (EUVE) astronomical satellite. The instrument is novel in design, consisting of three plane reflection gratings mounted in the converging beam behind a grazing incidence telescope. This configuration is based on new varied line-space (VLS) gratings which have recently been proposed. A sample EUVE grating has been mechanically ruled and experimentally characterized. It recovered over 80% of the theoretical efficiency of perfectly formed grooves, reaching 38% absolute at a wavelength of 114 Å. The grating was used to construct a laboratory spectrographic version of the EUVE spectrometer and recorded the spectrum of helium from 228 to 320 Å. The spectral resolution was λ/Δλ ∼ 2000 and the image heights were ∼10 sec of arc. Individual spots were ∼25 × 50 μm, which is a significant improvement over existing grazing incidence spectrographs. A line profile measurement at 1 Å away from first order 304 Å showed <1.5%/ Å of grating stray light and a rapid decline toward the wings. In visible light, no grating stray or ghost light could be seen. Three flight spectrometer channels in combination span the 70–760-Å band with an effective collecting area of 0.3–1 cm^2 over the 80–600-Å region. The spectrometer has an inherent resolution of λ/Δλ ∼ 300, but if combined with a worst-case satellite performance will yield a spectral resolution of λ/Δλ = 110–240 and a spatial resolution of 1–2 min of arc. For a 40,000-sec observation, the average 3σ sensitivity to continuum flux is ∼2 × 10^−27 erg/cm^2/sec/Hz. This is a factor of 100 dimmer than a bright known EUV source and is comparable to the sensitivity of the all-sky survey which will be carried out on the EUVE. At a 5σ detection threshold, the spectrometer sensitivity to individual spectral lines is 1–4 × 10^−3 photons/cm^2/sec, which is a factor of 50 better than available with the EUVE wide bandpass telescopes. Simulated observations of two known classes of extrasolar EUV sources reveal rich spectra. During a six-month spectroscopic phase, target selection will be conducted by guest investigators chosen by NASA.

Thin metallic foils of antimony and titanium have been investigated in an attempt to develop an EUV filter with a bandpass from 350 to 550 Å. A composite filter has been developed composed of antimony sandwiched between two titanium foils. The transmissions of sample composite foils and of pure titanium foils from 130 to 1216 Å are presented. The absorption coefficients of antimony and titanium and the effect of titanium oxide on the transmission are derived. The composite filter has been found to be quite stable and mechanically rugged. Among other uses, the filter shows substantial promise for EUV astronomy.

A satellite-borne extreme-ultraviolet airglow spectrometer is described covering the 275–1420-Å range with 8-Å resolution. The spectrometer is of near normal incidence Rowland circle design and employs a holographically ruled concave grating. The detector is a microchannel plate with resistive anode providing a continuous readout of any 650-Å ground-commandable subset of the total bandpass. This simultaneous wide spectral coverage results in a factor of 80 increase in sensitivity over a fixed exit slit design of equivalent resolution.

The throughput and imaging properties of one of a new class of grazing incidence spectroscopic telescope are examined with a Monte Carlo ray tracing technique. The results are compared with Wolter Schwarzschild type II telescopes of similar size. The image quality of this telescope is comparable, and the control of the off-axis light is superior to the Wolter Schwarzschild design.

A four-channel photometer sensitive to two solar EUV lines which are resonantly scattered by helium gas was developed for flight on the Apollo-Soyuz Test Project. Two channels observed the 58.4-nm line of He i and used helium gas resonant absorption cells to determine the intensities of the center and wings of that line. The other two channels observed the 30.4-nm line of He ii. The instrument surveyed much of the celestial sphere during a series of slow rolling maneuvers by the Apollo spacecraft. The experiment operated properly, and usable data were obtained. Study of the distributions of flux seen, and of the ratio of 58.4-nm fluxes seen with gas cells full and empty, will refine current understanding of several poorly known properties of the local interstellar medium. Study of the 30.4-nm flux distribution will refine present knowledge of the structure of the earth’s plasmasphere.