Methods for the measurement of frequency and stability of laser generators of submillimeter oscillations
Frequency and stability measurements of IF signals generated between laser far IR radiations and conventional oscillators
Frenkel, L.↗
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A microwave-biased millimeter- and submillimeter-wave detector using InSb.
Description of a high-purity n-type indium antimonide sample mounted in a reentrant cavity, cooled to 4.2 K, and operated as a millimeter-wave detector. The scheme utilizes a down-conversion process, and free-carrier absorption is the mechanism responsible for the detection process. Power applied at the millimeter-wave frequency causes a change in the material conductivity, which in turn causes a change in the X-band power absorption. Cavity perturbation techniques are used to analyze the scheme. The detector was operated successfully at frequencies between 35 and 150 GHz with no long-wavelength or short-wavelength cutoff observed. The scheme offers a fast, highly sensitive, and rugged detector with low conversion loss.
Eldumiati, I. I.↗
Further measurements of the submillimeter background at balloon altitude.
Results of measurements of the far-infrared background radiation made with a balloon-borne radiometer at an altitude of 44 km. Equivalent blackbody temperatures were obtained for the background radiation in three bandwidths: 1 to 11.5 per cm, 1 to 13.5 per cm, and 1 to 18.5 per cm. The total measured flux in the largest of these bandwidths is dominated by the atmospheric emission by ozone and water. The data obtained confirm the results of prior flights, in particular, that a substantial amount, and perhaps all, of the radiation above 13 per cm is due to the atmosphere.
Muehlner, D. J.↗
Design and analysis of optically pumped submillimeter waveguide maser amplifiers and oscillators
The design and experimental measurements are described of an optically pumped far-infrared (FIR) waveguide maser; preliminary measurements on a FIR waveguide amplifier are presented. The FIR maser was found to operate satisfactorily in a chopped CW mode using either methanol (CH3OH) or acetonitrile (CH3CN) as the active molecule. Two other gases, difluoroethane and difluoroethylene, produced an unstable output with high threshold and low output power when operated in the chopped CW mode. Experimental measurements include FIR output versus cavity length, output beam pattern, output power versus pressure, and input power. The FIR output was the input to an amplifier which was constructed similar to the oscillator. An increase of 10% in output power was noted on the 118.8 microns line of methanol.
Galantowicz, T. A.↗
Measurement of the spectrum of the submillimeter cosmic background
The spectrum of the night sky has been measured in the wave number range from 3 to 40 per cm using a fully calibrated liquid-helium-cooled balloon-borne spectrophotometer at an elevation of 39 km. A model based on the known molecular parameters was used to subtract the atmospheric emission. In the range from 4 to 17 per cm, the spectrum of the background radiation is that of a blackbody with a temperature of about 2.99 K.
Woody, D. P.↗
Far-infrared and submillimeter observations of the planets
Broadband observations in several passbands between 30 and 500 microns of Mercury, Venus, Mars, Jupiter, Saturn, and Uranus are presented. The best agreement between the data and various thermal models of Mars, Jupiter, and Uranus is obtained with a slightly cooler absolute temperature scale than that previously adopted by Armstrong et al. (1972). The effective temperature of Uranus is 58 + or - 2 K, which is in agreement with its solar equilibrium temperature. The existence of an internal energy source for Saturn has been reconfirmed; its output must lie within the range of 0.9 to 3.2 times the absorbed solar flux. A depression exists in the spectra of Jupiter, Saturn, and Uranus between 80 and 300 microns, which may be a result of NH3 opacity.
Loewenstein, R. F.↗
Detection of submillimeter /870-micron/ CO emission from the Orion molecular cloud
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Phillips, T. G.↗
Submillimeter observations of the galactic center
A 15 by 15 arcmin region surrounding Sgr A has been mapped at a mean wavelength of 540 microns. The principal feature is a ridge about 10 arcmin long running parallel to the galactic equator and approximately centered on Sgr A but with no peak at that point. The ridge coincides with the 25- and 55-km/s clouds seen in molecular line observations. The mass of the clouds is estimated, and their positions with respect to the galactic center are discussed.
Hildebrand, R. H.↗
Airborne infrared and submillimeter astronomical polarization measurements at different wavelengths
Because observations of the Kleinmann-Low region of the Orion Nebula reveal significant polarization in the wavelength range from 1 to 13 micron m, polarization at wavelengths greater than 15 micron were investigated. Far infrared polarization measurements were made of a number of sources using an instrument mounted at the bent cassegrain focus of the Kuiper Airborne Observatory's 90 cm telescope. About two hours of data were obtained on the Orion Nebula on each of two flights, and more careful calibration on Jupiter (assumed to be unpolarized) were obtained on both nights. The data on Orion and Jupiter for three filters are presented. Possible explanations are suggested for reconciling the high polarization observed by others in 1974 with the lower values obtained in this study.
Harwit, M.↗
Submillimeter brightness temperatures of Venus, Jupiter, Uranus, and Neptune
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Whitcomb, S. E.↗
A large-beam sky survey at millimeter and submillimeter wavelengths made from balloon altitudes
A survey has been made of a quarter of the celestial sphere from balloon altitudes with a telescope having a 1.6-deg beamwidth and two spectral bands: 3-10 kaysers and 10-25 kaysers. The limiting sensitivity of the survey was 10,000 Jy. The galactic disk was detected from 358 to 45 deg galactic longitude. The total far-infrared flux from several regions on the galactic plane measured in this survey is 5-10 times larger than that observed by others using smaller beamwidths and small-amplitude spatial chopping, indicating that a substantial part of the emission comes from extended sources. Two other extended sources were also observed, one in the Cygnus region and the other a spur running off the galactic plane at 130 deg galactic longitude toward the north celestial pole. In addition, lower limits for the spectral index of interstellar dust emission are presented.
Owens, D. K.↗
Bulk submillimeter-wave mixers: Strain and superlattices
Strained germanium crystals, doped with gallium, were used as heterodyne mixers at THz frequencies, with infrared bandwidths approaching a GHz. The mixer performance (conversion loss and mixer noise) was analyzed in terms of nonlinearities associated with acceptor levels and with relaxation rates of free holes. Comparison was made with similar mixers employing low lying donor levels in high purity GaAs and with hot electron InSb mixers.
Litvak, M. M.↗
Low-pass interference filters for submillimeter astronomy
Low-pass (long-wave transmitting) interference filters, suitable for broadband photometric observations, previously have been constructed from series of capacitive grids stretched on thin Mylar. These filters have the desired optical properties of high transmission, sharp cut-ons, and good blocking at short wavelengths. Their designs, however, do not scale from one wavelength to another and their performance can deteriorate at low temperatures due to differential contraction of the dielectric backing and the supporting structure. The deviation of these early filters from the predicted scaling was due primarily to the difference in refractive index between the backing material and the medium between the grids. In the present paper, filters are described in which dielectric spacers are used, instead of air, as the medium between the grids. This technique has improved the scaling and has reduced the distortion from differential contraction.
Whitcomb, S. E.↗
Submillimeter wave survey of the galactic plane
The survey measured, over virtually the entire galactic plane, the distribution and basic physical conditions of the coolest dust component of the interstellar medium. The instrument designed for observations of extended, low surface brightness continuum emission consisted of a balloon borne, gyro stablized, 1.2 m Cassegrain telescope and a liquid cooled photometer. The design, integration, tests, and flight operation of the survey are presented.
Cheung, L. H.↗
Laboratory measurements of millimeter and submillimeter transitions of sodium hydride and sodium deuteride
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Sastry, K. V. L. N.↗
Submillimeter observations of solar limb-brightening in the total solar eclipse of 31 July 1981
Eight flights of the Kuiper Airborne Observatory (KAO) were devoted to solar observation. The successful observation of a total solar eclipse was accomplished. The observations were made simultaneously at 30, 50, 100, and 200 microns. The successful adaptation of the KAO for solar observations thus provided the most detailed data to date in this spectral band. The results from a preliminary analysis of the KAO data are summarized: (1) the 200 micron limb is extended about 3 arc sec above the 30 micron limb, indicating the prescence of cool dense material up to the altitudes of spicules; (2) strong radial darkening of the quiet sun intensity profile appeared at 200 microns, probably an indication that hot material in the low chromosphere is recessed into vertical magnetic flux tubes embedded in a cooler nonmagnetic substrate, which obscures the heated material approaching the limb; (3) active regions were observed to undergo a strong increase in contrast above the quiet sun background at wave lengths of 100 microns and longer; and (4) the moon was mapped for use as a photometric standard for determining the absolute intensity of the sun in all four wavelength bands.
Becklin, E. E.↗
Optically pumped submillimeter-waves and applications
Rapid development of optically pumped lasers has shown the potential to be used as a source for a high resolution spectrometer. In this connection, a compact, stable FIR laser was designed, fabricated, and assembled, integrating both the pump laser and the FIR cavity in the same mechanical structure for its improved (both thermal and mechanical) stability and mobility. Performance of the mixer structure which was designed and constructed for the evaluation of the Schottky diodes was found to be satisfactory. The feasibility of generating tunable sideband for molecular spectroscopy studies was demonstrated.
Dutta, J. M.↗
The JPL millimeter, submillimeter and microwave line catalog
The catalog includes molecules of interest in the interstellar medium, in planetary atmospheres and in the Earth's atmosphere. Different units than those on the AFGL tape are used. For citing line frequencies in the microwave region. Either the experimental errors or the propagation of errors from the fit are included on the tape. This gives an estimate of how accurate the frequencies are. The intensity units are defined as follows: the logarithm of the intensity unit is the cross section times the frequency in MHz. This is essentially the same unit as on the AFGL tape, but contains fewer factors of the speed of light. The catalog is available to the scientific community either as a tape or on microfiche (filmed in frequency sorted and molecule sorted format).
Pickett, H.↗