Theory of an ellipsometric technique for investigating weakly absorbing substances.
Ellipsometer measurements to obtain estimates of refractive index and thickness of weakly absorbing isotropic, homogeneous slab
OPTICAL THICKNESS↗
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The atmospheric pressure at the surface of Mars.
Martian surface atmospheric pressure via photometric observations of Phobos eclipses
OPTICAL ABSORPTION↗
Elemental abundance determinations for meteors by spectroscopy.
Relative elemental abundance determinations for meteors by spectroscopy are discussed. Relative abundances of spectroscopically accessible elements of four major shower meteors and one sporadic meteor are presented. A sporadic meteor with dominant sodium radiation and an iron-deficient sporadic meteor are analyzed. Empirical and theoretical tests for self-absorption in optical meteor plasmas have been conducted. Both ionization and incomplete dissociation are found to severely deplete certain neutral atoms from meteor plasmas.
Harvey, G. A.↗
Interstellar lines in the spectra of four stars
Observations of optical interstellar absorption lines arising from Na I, K I, and/or Ca II are reported in the spectra of HD 72127, Iota(1) Sco, 102 Her, and 6 Cas. Line components showing strikingly large Ca II/Na I ratios are found toward HD 72127 and are verified for 102 Her. The absorption toward Iota(1) Sco and 6 Cas illustrates features of the local galactic distribution of interstellar gas.
Hobbs, L. M.↗
The ionization equilibrium inside the RHO Ophiuchi cloud
Observational technology is now reaching the point where optical absorption-line studies of dark interstellar clouds are becoming feasible. Such studies are of great interest. In particular, it will be important to discover the degree of depletion which has occurred in dark clouds. In order to assess depletions on the basis of observations of a limited range of ionization stages, it is necessary to analyze the ionization balance. The present investigation is concerned with such an analysis. The two key parameters necessary for deducing the ionization balance are the electron density and the radiation field intensity. A summary is provided regarding the existing data on the cloud density using data from the literature, and the radiation field intensity is derived from the observed H2 rotational excitation. The implications of both the density and radiation field data for the ionization balance of several species are discussed. It is found that for all species treated the first ion is dominant in the line of sight toward HD 147889.
Snow, T. P., Jr.↗
Neutral interstellar gas in the lower galactic halo
The optical interstellar absorption lines of Ti II, Ca II, Na I, and the 21 cm emission line of H I were observed at high resolution and high detection sensitivity toward none pairs of nearly aligned distant halo stars and foreground disk stars with well determined distances. Analysis of the column densities, velocities, and the directly determined variation of the titanium abundances with z-distance leads to a general picture of the neutral interstellar material in the lower galactic halo. Two types of gas with distinct distribution, kinematics, and abundances are found, a thick, low velocity disk (type I) extending from the plane to well beyond the thin disk of OB stars, and a high velocity, much less strongly depleted gas (type II) observed only at high z-distances, which constitutes at least 24 percent of the mass of the halo gas. The implications of this model for the observed neutral gas are discussed both in terms of the possible origins of the observed gas and in its comparison with quasi stellar object absorption lines. Previously announced in STAR as N82-29246
Albert, C. E.↗
Transmittance and reflectance of crystalline quartz and highand low-water content fused silica from 2 microns to 1 mm
The transmittances and reflectances of cultured crystalline quartz, Suprasil, Suprasil W, and Infrasil were compared over the wavelength region from 2 to 1000 microns. The high-water content of Suprasil and the low-water content of cultured crystalline quartz, Suprasil W, and Infrasil were determined by their transmittances measured at 2.73 microns where water content causes high absorption in optical materials. The fact that the fused silicas, both with high- and low-water content, had identical far-IR transmittances and that their transmittances were greatly inferior to that of crystalline quartz led to the conclusion that their inferior transmittance is due to their amorphous structure and not to their water content.
Heaney, J. B.↗
Local Interstellar Medium. International Astronomical Union Colloquium No. 81
Helium and hydrogen backscattering; ultraviolet and EUV absorption spectra; optical extinction and polarization; hot gases; soft X-ray observations; infrared and millimeter wavelengths; radio wavelengths and theoretical models of the interstellar matter within about 150 parsecs of the Sun were examined.
Kondo, Y.↗
Interstellar C2, CH, and CN in translucent molecular clouds
Optical absorption-line techniques have been applied to the study of a number of translucent molecular clouds in which the total column densities are large enough that substantial molecular abundances can be maintained. Results are presented for a survey of absorption lines of interstellar C2, CH, and CN. Detections of CN through the A 2Pi-X 2Sigma(+) (1,O) and (2,O) bands of the red system are reported and compared with observations of the violet system for one line of sight. The population distributions in C2 provide diagnostic information on temperature and density. The measured column densities of the three species can be used to test details of the theory of molecule formation in clouds where photoprocesses still play a significant role. The C2 and CH column densities are strongly correlated with each other and probably also with the H2 column density. In contrast, the CN column densities are found to vary greatly from cloud to cloud. The observations are discussed with reference to detailed theoretical models.
Black, John H.↗
Evaluation of the feasibility of a far-infrared laser based on intersubband transitions in GaAs quantum wells
The threshold current and quantum efficiency are calculated for an FIR injection laser based on intersubband transitions in GaAs single quantum wells. By considering the balance of gain against the free carrier and transverse optical phonon absorption, and the intersubband transition time, the wavelength dependence of the threshold current is calculated. For the wavelength range 50-120 microns, the required threshold currents are the lowest and have reasonable values of 1-10 kA/sq cm. The threshold quantum efficiency in that range is expected to be about 0.0001.
Borenstain, Shmuel I.↗
Detection of gaseous oxygen using temperature tuned laser diodes
The development of an optical differential absorption technique using laser diodes is discussed. The technique is being developed as a solution to overcome the difficulties imposed by conventional liquid rocket propulsion system leak detection such as damage to the engine, cumbersome equipment, and excessive amounts of time. The detection of O2 at atmospheric pressure and temperature using laser diodes is demonstrated. Also, it is shown that, by temperature tuning the laser diode, the wavelength was shifted to a level where the oxygen absorption peaks are found. The levels of transmission determined via experimental means and those calculated from spectral data are found to be in close agreement.
Fox, Curtis W.↗
Possible identification of a cluster of galaxies at redshift z = 3.4
We report the possible detection of a cluster of 16 radio-quiet galaxies at z = 3.4, identified in the field around the optically thick absorption system toward Q0000-263 at z(sub abs) = 3.390. Two of them, a Lyman alpha emitter at z = 3.428 and the galaxy responsible for the absorption system, have redshifts spectroscopically confirmed. The other 14 galaxies identified using a multicolor imaging technique designed to detect sources in the redshift interval 3 approximately less than z approximately less than 3.5 which are characterized by a Lyman discontinuity in an otherwise flat spectrum, have broad-band spectral energy distributions identical to the two galaxies with known redshift. They are spatially distributed in two apparent clumps, around the damped absorber and the Lyman alpha galaxy, respectively. A clustering analysis excludes with 98.8% confidence that this association is a realization of a Poissonian distribution and confirms that the observed clumps are real. The implications are that the 16 galaxies are members of a cluster at z approximately equals 3.4, by far the most distant ever detected. An estimate of the mass bounded in stars of this cluster is 3 x 10(exp 12) solar mass (q(sub 0) = 0 and H(sub 0) = 50 km/s/Mpc throughout this Letter), while the total mass (baryonic + dark) is 6 x 10(exp 14) solar mass. We also estimate that at z = 3.4 the correlation length is 2.2 Mpc, which, compared to the present value of 11 Mpc, suggests that the clustering evolution is still close to the linear regime.
Giavalisco, Mauro↗
Ground-Based Measurements of Stratospheric Composition from Mt. Barcroft, California
The MkIV is an FTIR spectrometer designed and built at JPL in the 1980's for remote sensing the composition of the Earth's atmosphere by solar absorption spectrometry. Optically, MkIV is very similar to the JPL ATMOS instrument, which flew three times on the Space Shuttle. Both use double-passed configurations with a KBr beamsplitter and compensator, in order to cover the mid-infrared. The main advantage of the MkIV is that it uses two detectors in parallel, a HgCdTe photoconductor for the long wavelengths and an InSb photodiode for the short wavelengths, allowing the entire 650 to 5650/cm region to be measured simultaneously. At a 10 kHz sampling rate, each 130 cm OPD interferogram takes 3 minutes to acquire. This paper describes how the MkIV instrument was adapted for remote operation from the Barcroft site, where the harsh winter conditions make access difficult. Some of the main technical challenges will be discussed including, (i) operation from solar panels and batteries, (ii) cooling the detectors with LN2, (iii) instrument control and monitoring over a cellular phone, and (iv) data storage, processing and analysis. Finally, MkIV spectra measured from Barcroft are compared with those measured from JPL to highlight the advantages of the higher altitude site.
Toon, G. C.↗
The Importance of Optical Pathlength Control for Plasma Absorption Measurements
An inductively coupled GEC Cell with modified viewing ports has been used to measure in-situ absorption in CF4 plasmas via Fourier Transform Infrared Spectroscopy, and the results compared to those obtained in a standard viewport configuration. The viewing ports were modified so that the window boundary is inside, rather than outside, of the GEC cell. Because the absorption obtained is a spatially integrated absorption, measurements made represent an averaging of absorbing species inside and outside of the plasma. This modification is made to reduce this spatial averaging and thus allow a more accurate estimation of neutral species concentrations and temperatures within the plasmas. By reducing this pathlength, we find that the apparent CF4 consumption increases from 65% to 95% and the apparent vibrational temperature of CF4 rises by 50-75 K. The apparent fraction of etch product SiF4 decreases from 4% to 2%. The data suggests that these density changes may be due to significant temperature gradients between the plasma and chamber viewports.
Cruden, Brett A.↗
Development of a cw-laser-based cavity-ringdown sensor aboard a spacecraft for trace air constituents
The progress in the development of a sensor for the detection of trace air constituents to monitor spacecraft air quality is reported. A continuous-wave (cw), external-cavity tunable diode laser centered at 1.55 micrometers is used to pump an optical cavity absorption cell in cw-cavity ringdown spectroscopy (cw-CRDS). Preliminary results are presented that demonstrate the sensitivity, selectivity and reproducibility of this method. Detection limits of 2.0 ppm for CO, 2.5 ppm for CO2, 1.8 ppm for H2O, 19.4 ppb for NH3, 7.9 ppb for HCN and 4.0 ppb for C2H2 are calculated.
NASA Discipline Life Sciences Technologies↗
Biogeochemical and Optical Analysis of Coastal DOM for Satellite Retrieval of Terrigenous DOM in the U.S. Middle Atlantic Bight
Estuaries and coastal ocean waters experience a high degree of variability in the composition and concentration of particulate and dissolved organic matter (DOM) as a consequence of riverine/estuarine fluxes of terrigenous DOM, sediments, detritus and nutrients into coastal waters and associated phytoplankton blooms. Our approach integrates biogeochemical measurements (elemental content, molecular analyses), optical properties (absorption) and remote sensing to examine terrestrial DOM contributions into the U.S. Middle Atlantic Bight (MAB). We measured lignin phenol composition, DOC and CDOM absorption within the Chesapeake and Delaware Bay mouths, plumes and adjacent coastal ocean waters to derive empirical relationships between CDOM and biogeochemical measurements for satellite remote sensing application. Lignin ranged from 0.03 to 6.6 ug/L between estuarine and outer shelf waters. Our results demonstrate that satellite-derived CDOM is useful as a tracer of terrigenous DOM in the coastal ocean
Mannino, A.↗
Cloud (and Aerosol) Information Content Analysis for EPIC/DSCOVR's Oxygen A- and B-band Channels
No abstract available
oxygen↗