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OAO data between 2000 A and 3600 A, obtained by the Wisconsin experimental package objective grating scanning spectrometer, are used to set upper limits to the abundances of many minor constituents in the atmospheres of Mars, Jupiter, Saturn, and Venus.
Spectral observations of the stars Alpha Canis Majoris, Gamma Orionis, Kappa Orionis and Alpha Leonis have been obtained in the range 1150-4000 A, using rocket borne spectrometers. The payloads have a 13-inch diameter telescope, a rotatable concave diffraction grating, and three pulse counting photomultiplier photometers. The observations are systematically lower than those of Carruthers (1968) at 1270 A, of Smith (1967) at 1376 A, and of Campbell (1970) at 2150 and 2550 A. The data are also about 15 percent lower than the ground-based photometry reported by Schild, Peterson and Oke (1971). The OAO-2 short wavelength scanner calibration agrees with the alpha Leo observations, but disagrees for Kappa Ori and Gamma Ori.
The development of experimental setups and procedures is considered for calibrating photosensitive devices in the spectral range 1022 to 2500 A for which no direct calibration techniques exist. An indirect technique that uses a sodium salicylate detector calibrated outside this range was developed for use as a secondary standard. The primary standard was a xenon-filled ionization chamber, which is an absolute standard over the wavelength interval 972 to 1022 A. Measurements made by this method were checked at 1470 A with a xenon lamp and at 2537 A with a mercury arc lamp and a 0.5 m blaze monochromator with a grating blazed at 2000 A. The overall accuracy of the measurements was + or - 40 percent or better.
Grating spectra of the North Equatorial Belt of Jupiter between 4.5 and 5.1 microns, obtained with a nominal resolving power of 180, are presented. An absorption feature centered at 4.73 microns and not due to a known constitu ent has been found. Its possible identification is discussed.
Measurement of the relative cross section for photodetachment of electrons from PH2(-) in the wavelength region 725 to 1020 nm (1.71 to 1.22 eV). An ion cyclotron resonance spectrometer was used to generate, trap, and detect the negative ions, and two light sources were employed to study photodetachment: a 1000-W xenon arc lamp with a grating monochromator and a continuously tunable laser. A single sharp threshold in the cross-section curve was observed, and a detailed analysis yielded an electron affinity value of 1.25 plus or minus 0.03 eV.
A number of high-quality spectra of Mars, Jupiter, the combined disk and rings of Saturn, as well as lower-quality spectra of Venus, have been obtained with an objective-grating spectrometer of the Wisconsin Experiment Package of OAO-2. An intercomparison of the Mars, Jupiter, and Saturn spectra has failed to disclose any discrete planetary absorptions. Continuous albedos have been derived for the four planets by using OAO-2 observations of G-type stars for wavelengths greater than 2700 A. The geometric albedo of Mars shows a steady increase below 3500 A which appears to be due to Rayleigh scattering combined with a decreasing surface reflectivity. The albedos of Venus, Jupiter, and Saturn show a maximum in reflectivity in the region of 2500 A.-
Use of a 0.5-m focal length, plane grating monochromator to measure the radiance of spectral radiation emanating from regions downstream of a mercury bombardment thrustor in the wavelength range investigated was 2800 to 6000 A. This radiation was due primarily to the radiative decay of excited mercury atoms exhausted from the thrustor. Radiance values ranged from 10 to the minus 11th to 10 to the min scm/ster varying with wavelength. For resonant radiation, the spectral radiance may exceed 10 to the minus 8th W/sq cm/ster. From such radiance measurements, it was concluded that the thrustor background radiation should not interfere with the control functions of a star tracker viewing through the thrustor exhaust, provided that the tracker is designed to operate with a sufficiently small field of view. Problems may be encountered, however, during the spacecraft acquisition phase where a larger field of view may be required. Here the thrustor exhaust radiation may be comparable to the star light flux. This problem may be circumvented by locating the tracker view axis so as not to view downstream of the thrustor.
Use of a Fabry-Perot interferometer in a Ramsay mount in tandem with an echelle Hilger monochromator with pinholes instead of slits. The instrument, URSIES, is enclosed within a pressure chamber filled with Freon. Photoelectric pulse counting techniques and pressure scanning are used to record the spectrum. This design has four basic advantages: (1) the resolution of the scanner is variable from 5.0 to 0.005 A, and the effective wavelength range is quite broad, from 3500 to 13,000 A; (2) a light gain of ten over conventional grating scanners at resolutions of 0.1 A or better is achieved; (3) very low levels of light from outside the wavelength passband reach the detector; for a resolution of 0.03 A at 6000 A this level is 5%; and (4) there are very low levels of scattered light from the pinholes when extended sources are observed. The scattered light from the instrument at the edge of the solar disk is found to be less than 1% from 4000 to 11,000 A. Measurements demonstrating these advantages are discussed.
The relative cross section for the gas-phase photodetachment of electrons has been determined for NH2(-) in the wavelength region of 1195 to 1695 nm and for AsH2(-) in the region from 620 to 1010 nm. An ion cyclotron resonance spectrometer was used to generate, trap, and detect negative ions. A 1000-W xenon arc lamp with a grating monochromator was used as the light source, except for one series of experiments in which a tunable laser was employed. Single sharp thresholds were observed in both cross sections, and the following electron affinity values were determined: 0.744 (plus or minus 0.022) eV for NH2. and 1.27 (plus or minus 0.03) eV for AsH2.
An f/2 objective-grating spectrograph aboard an Aerobee rocket recorded a faint image of Comet Tago-Sato-Kosaka (1969g) in L-alpha emission. Some sharpening of the image and reduction of film grain noise was accomplished by multiplying the picture's Fourier transform by an optimum filter function. After this processing, which was carried out digitally, the L-alpha comet image appeared as a nearly circularly symmetric diffuse glow approximately 800,000 km in diameter. There was also the suggestion of a faintly visible core of emission whose dimensions are less than 100,000 km. The sublimation of ice in the nucleus of the comet and the subsequent dissociation of the free water molecules by sunlight could produce a large cloud of hydrogen atoms around the comet. Resonant reradiation of solar L-alpha emission by this cloud is probably responsible for the most of the observed emission.
The relative cross section for the gas phase photodetachment of an electron from SeH(-) was determined in the wavelength region 428 to 578 nm. An ion cyclotron resonance spectrometer was used to generate, trap, and detect the negative ions, and a 1000-W xenon arc lamp with a grating monochromator was employed as the light source. The cross section exhibited two sharp thresholds, whose positions remained unchanged for the photodetachment of SeD(-). As a result of these thresholds, the electron affinity and the spin-orbit coupling constant were evaluated.
A hologram has been made using a surface plasmon resonance wave as the reference beam. The surface wave was stimulated on a 1200-line/mm aluminum reflection grating that was coated with a thin layer of high-resolution photographic emulsion. Experimental results are presented.
A simple technique for sequentially Q-switching molecular lasers is discussed in which an optical scanner is used as an optical folding element in a laser cavity consisting of a stationary diffraction grating and partially reflecting mirror. Sequential Q-switching of a conventional CO2 laser is demonstrated in which over sixty-two transitions between 9.2 and 10.8 microns are observed. Rapid repetition rates (200 Hz) and narrow laser pulses (less than 5 microsec) allow conventional signal processing techniques to be used with this multiwavelength laser source which is a versatile tool for laser propagation studies, absorption spectroscopy, and gain measurements. Results of a preliminary experiment demonstrating the utility of measuring selective absorption of CO2 laser wavelengths by C2H4 are shown.
Orbiting Astronomical Observatory data between 2000 and 3600 A, obtained by the Wisconsin Experimental Package objective grating scanning spectrometer, are used to set upper limits to the abundances of many minor constituents in the atmospheres of Mars, Jupiter, Saturn, and Venus.
A computerized simulation of a planar phased array of circular waveguide elements is reported using mutual coupling and wide angle impedance matching in phased arrays. Special emphasis is given to circular polarization. The aforementioned computer program has as variable inputs: frequency, polarization, grid geometry, element size, dielectric waveguide fill, dielectric plugs in the waveguide for impedance matching, and dielectric sheets covering the array surface for the purpose of wide angle impedance matching. Parameter combinations are found which produce reflection peaks interior to grating lobes, while dielectric cover sheets are successfully employed to extend the usable scan range of a phased array. The most exciting results came from the application of computer aided optimization techniques to the design of this type of array.
The Mariner Mars 1971 ultraviolet spectrometer is an Ebert-Fastie type of the same basic design as the Mariner Mars 1969 instrument. Light enters the instrument and is split into component wavelengths by a scanning reflection diffraction grating. Two monochrometer exit slits allow the use of two independent photomultiplier tube sensors. Channel 1 has a spectral range of 1100 to 1692 A with a fixed gain, while Channel 2 has a spectral range of 1450 to 3528 A with an automatic step gain control, providing a dynamic range over the expected atmosphere and surface brightness of Mars. The scientific objectives, basic operation, design, testing, and calibration for the Mariner Mars 1971 ultraviolet spectrometer are described. The design discussion includes those modifications that were necessary to extend the lifetime of the instrument in order to accomplish the Mariner Mars 1971 mission objectives.
The use of a very long straight entrance slit in an Ebert grating spectrometer with two plane mirrors at the shorter exit slit to increase the energy density is described. This system has been employed in a far ultraviolet rocket spectrometer to provide higher sensitivity than has been achieved previously. The imaging properties and required slit and mirror adjustments are presented. Experimental results are included.
Discussion of certain design aspects of the coude spectrograph, and description of the coude scanner that uses some of the spectrograph optics. The configuration of the large echelle grating used is reviewed along with the systems of computer scanner control and data handling.