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NASA NTRS1975

Io's sodium emission cloud

Strong evidence that Io's sodium emission is due to resonant scattering is given by our observations which show a monotonic increase of emission intensity with residual solar intensity. In addition we detected no emission during three eclipse observations of Io. We propose a resonant scattering model with two spacial components comprising an optically thick atmosphere extending 1000 km above Io's surface surrounded by an optically thin cloud which forms a partial torus around Jupiter. In this model, sodium atoms are sputtered from Io's surface by heavy energetic ions which are accelerated in a plasma sheath around Io. The atoms sputtered from the surface collide with atoms in Io's atmosphere so the equipartition of kinetic energy is established. During Io's day, sodium and other atmospheric constituents are ionized, giving rise to the ionosphere observed by Pioneer 10. Atoms escape by means of Jeans escape from the critical level, which is at the top of the atmosphere and the base of the cloud.

Macy, W. W., Jr.↗
NASA NTRS2019

Cyclotron Lines in Highly Magnetized Neutron Stars

Cyclotron lines, also called cyclotron resonant scattering features are spectral features, generally appearing in absorption, in the X-ray spectra of objects containing highly magnetized neutron stars, allowing the direct measurement of the magnetic field strength in these objects. Cyclotron features are thought to be due to resonant scattering of photons by electrons in the strong magnetic fields. The main content of this contribution focusses on electron cyclotron lines as found in accreting X-ray binary pulsars (XRBP) with magnetic fields on the order of several 1012 Gauss. Also, possible proton cyclotron lines from single neutron stars with even stronger magnetic fields are briefly discussed. With regard to electron cyclotron lines, we present an updated list of XRBPs that show evidence of such absorption lines. The first such line was discovered in a 1976 balloon observation of the accreting binary pulsar Hercules X-1, it is considered to be the first direct measurement of the magnetic field of a neutron star. As of today (end 2018), we list 35 XRBPs showing evidence of one ore more electron cyclotron absorption line(s). A few have been measured only once and must be confirmed (several more objects are listed as candidates). In addition to the Tables of objects, we summarize the evidence of variability of the cyclotron line as a function of various parameters (especially pulse phase, luminosity and time), and add a discussion of the different observed phenomena and associated attempts of theoretical modeling. We also discuss our understanding of the underlying physics of accretion onto highly magnetized neutron stars. For proton cyclotron lines, we present tables with seven neutron stars and discuss their nature and the physics in these objects.

Staubert, R.↗
NASA NTRS1972

Backscatter of solar resonance radiation. I.

Calculation of the angular dependence of the intensity of solar Lyman alpha resonantly scattered from neutral interstellar hydrogen which has penetrated the solar system. A simple model which essentially neglects temperature effects, but which includes gravity, radiation pressure, photoionization and charge exchange is used for this calculation. The results are then compared with the observations. The resonant scattering of He I 584 A is also treated.

Johnson, H. E.↗
NASA NTRS1973

Observations of the Helium II 304-A and Helium I 584-A atmospheric dayglow radiation.

Two photometers with bandpasses of 170 to 500 and 170 to 800 A were employed to observe dayglow emissions in the extreme ultraviolet (EUV) over an altitude range of 90 to 186 km. The emissions observed with these photometers are identified as resonantly scattered He I 584-A and He II 304-A radiations. At 186 km, 209 plus or minus 70 rayleighs of 584-A and 9.3 plus or minus 3.1 rayleighs of 304-A radiation were measured. These observations are compared with theoretical calculations of resonance scattering of solar emissions from geocoronal He and He(+). Using the Jacchia (1971) atmospheric model for He, it is found that the observed brightness of the 584-A emission requires that the solar 584-A line width be 0.014 plus or minus 0.004 A. In this model the maximum overhead brightness of 584-A dayglow would occur at 900 km, and its magnitude would be 1.9 plus or minus 0.6 kR. The authors' observation of 304-A brightness requires that the overhead column density of the He(+) ions be 4.2 x 10 to the 11th ions/sq cm column. This value is consistent with a constant-density plasmasphere model with a He(+) ion density of 320 ions/cu cm in the plasmasphere.

Kumar, S.↗
NASA NTRS1992

Lidar measurements using large liquid mirror telescopes

It is a well accepted practice in the discussion of lidars to compare systems by a performance factor given by the product of the transmitter power and receiver aperture. This form of the performance factor reflects the two key parameters that determine the amount of photons recorded from a given range bin; the amount of transmitted photons and the probability of collecting a scattered photon. We are interested in studying the propagation and breaking of gravity waves typically generated in the lower atmosphere. To study these waves requires high temporal and spatial resolution, as they have frequencies as high as 500 mHz and generate turbulent structures with vertical scales of less than 25 m. In the 80 - 100 km region of the atmosphere these measurements are most efficiently obtained by using resonance scattering from sodium atoms deposited by meteors. However, in the 30 - 80 km region, the most efficient scattering arises from molecules (Rayleigh scattering). Since the atmospheric scale height is nominally 7 km, this scattering becomes extremely weak above 60 km. Furthermore, present laser technology limits the power available for Rayleigh-scattering experiments to about 0.5 - 50 W. The transmitter for the lidar system under development at the University of Western Ontario uses a two-beam transmitter to simultaneously measure density perturbations and temperature from both Rayleigh and resonance scattering.

Sica, R. J.↗
NASA NTRS1973

Polarization of the 584- and 304-Angstrom emissions of helium in the geocorona and interplanetary medium

The polarization of the 584- and 304-A emissions of helium that have been resonantly scattered in the earth's atmosphere and in the interplanetary medium is discussed. It is shown that in the geocorona the simultaneous measurement of altitude profiles of the 584-A He dayglow intensity and polarization will test the hypothesis that the 584-A dayglow is excited by resonance scattering of sunlight from geocoronal helium. If this is indeed the major source of the 584-A dayglow emission, a simultaneous measurement of the polarization and the altitude profile of the intensity in the exosphere will uniquely determine the helium number density distribution as a function of altitude, and in the thermosphere it will alow a study of nondiffusive equilibrium processes. An attractive feature of this method is that the interpretation does not require a knowledge of the solar 584-A line center flux or line profile.

Kumar, S.↗
NASA NTRS1986

Far-ultraviolet background observations at high galactic latitude. II - Diffuse emission

A single spectrum, of extremely long integration time, is used to place stringent new limits on the diffuse far-UV background in the 500-1200 A region. This spectrum, obtained in the vicinity of the North Galactic Pole with the Voyager 2 UV spectrometer, can be explained solely on the basis of resonant scattering from interplanetary H I and He I. Limits on any additional sources of sky background radiation corresponding to 100-200 photons/sq cm per sec/sr per A for continuum emission and 6000 photons/sq cm per sec/sr for line emission are demonstrated. Comparisons of these upper limits with existing measurements and various potential source mechanisms are discussed. The first detection of resonantly scattered interplanetary H I Ly-gamma (973 A) emission is reported.

Holberg, J. B.↗
NASA NTRS1974

Pioneer 10 ultraviolet photometer observations at Jupiter encounter

A two-channel extreme ultraviolet photometer on Pioneer 10 was used to investigate hydrogen and helium emissions from the atmosphere of Jupiter and emissions associated with the Galilean satellites. The hydrogen Lyman alpha signal observed from Jupiter corresponded to 400 R in brightness. By using the results of Wallace and Hunten (1973), the eddy diffusion coefficient is found to be K = 3 x 10 to the (8 plus or minus 1) power. The He I 584-A emission rate was found to be 5.1 R. The radiative transfer problem for the resonantly scattered He I emissions was investigated in the coherent approximation. With these results, the observed brightness, and the derived eddy diffusion coefficient the He/H2 ratio in the mixing region of the atmosphere was found to be equal to 0.18 minus 0.12 or plus 0.46. Emissions attributed to H I Lyman alpha were found at the orbital radius of Io and appear to be due to resonance scattering by a toroidal cloud of H in orbit around Jupiter.

Carlson, R. W.↗
NASA NTRS1993

The Lyman alpha bulge of Jupiter - Effects of non-thermal velocity field

We outline for the first time the effect of such nonthermal line broadening processes as turbulence, random waves, convection, etc., on the shape and intensity of the H Ly-alpha line resonance scattered from the atmosphere of Jupiter. We show how a nonthermal velocity field confined to the bulge region, in the upper atmosphere of Jupiter, may account for most of the H Ly-alpha bulge features. Both the shape and the brightness of the Ly-alpha line from the bulge region as reported by the IUE instrument and the Voyager UV Spectrometer can be recovered assuming resonant scattering with a total atomic hydrogen of about 4 x 10 exp 17/sq cm, and a nonthermal component H of about 2 x 10 exp 15/sq cm above the thermopause.

Ben Jaffel, Lotfi↗
DOE OSTI2024

Non-resonant Bragg scattering four-wave mixing at near-visible wavelengths in low-confinement silicon nitride waveguides

Quantum state coherent frequency conversion processes—such as Bragg-scattering four-wave mixing (BSFWM)—hold promise as a flexible technique for networking heterogeneous and distant quantum systems. In this Letter, we demonstrate BSFWM within an extended (1.2-m) low-confinement silicon nitride waveguide and show that this system has the potential for near-unity frequency conversion in visible and near-visible wavelength ranges. Using sensitive classical heterodyne laser spectroscopy at low optical powers, we characterize the Kerr coefficient (∼1.55 W −1 m −1 ) and linear propagation loss (∼0.0175 dB/cm) of this non-resonant waveguide system, revealing a record-high nonlinear figure of merit (NFM = γ / α ≈ 3.85 W −1 ) for BSFWM of near-visible light in non-resonant silicon nitride waveguides. We predict how, at high yet achievable on-chip optical powers, this NFM would yield a comparatively large frequency conversion efficiency, opening the door to near-unity flexible frequency conversion without cavity enhancement and resulting bandwidth constraints.

Jaber, Nicholas (ORCID:000900070106809X)↗
NASA NTRS1977

Sodium D-line emission from Io - A second year of synoptic observation from Table Mountain Observatory

Measurements of sodium D-line emission from Io are reported which were made during synoptic patrols of the 1975 and 1974 apparitions. Corrected equivalent widths of the D lines are plotted against the satelliite's orbital phase reckoned from superior heliocentric conjunction, and quantitative results of selected patrol observations are provided. The results indicate that: (1) resonant scattering is most likely the dominant emission mechanism; (2) the mechanism which injects neutral sodium into the space immediately around Io underwent no major secular variation in the period between the two apparitions; (3) a less pronounced asymmetry between the peak emission rates at 90-deg and 270-deg orbital phases is present in the selected data; and (4) the measured D2/D1 intensity ratios are consistent with a value of 1.6 + or - 0.3, which corresponds to a value of the order of unity for the maximum optical depth possible for resonant scattering the D1 line center. It is suggested that an unexplained scatter of about 20% in the general emission levels is due to a variation in the ionization rate.

Bergstralh, J. T.↗
NASA NTRS1971

Simultaneous measurements of the hydrogen airglow emissions of Lyman alpha, Lyman beta, and Balmer alpha.

Comparison of Lyman-alpha, 740- to 1050-A, and Balmer-alpha airglow measurements made at 134 deg solar-zenith angle on Oct. 13, 1969, with resonance-scattering models of solar radiation. Model comparison with Lyman-alpha data fixes the hydrogen column abundance over 215 km to 2 x 10 to the 13th per cu cm within a factor of 2. Differences between the Lyman-alpha model and data indicate a polar-equatorial departure from spherical symmetry in the hydrogen distribution. A Lyman-beta model based on the hydrogen distribution found to fit the Lyman-alpha data fits the spatial variation of the 740- to 1050-A data well from 100 to 130 km, but it does not fit the data well at higher altitudes; thus the presence of more rapidly absorbed shorter-wavelength radiation is indicated. This same resonance-scattering model yields Balmer-alpha intensities that result in good spatial agreement with the Balmer-alpha measurements, but a fivefold increase in the measured solar line center Lyman-beta flux is required (as required for the Lyman-beta measurement). The intensity ratio of Lyman-beta and Balmer-alpha at night is found to be a simple measure of the hydrogen optical depth if measurements with good accuracy can be made in the visible and ultraviolet spectrum.

Weller, C. S.↗
NASA NTRS1980

A multiphoton treatment of near resonant light scattering in intense fields

The scattering by a two-state atom of monochromatic light of arbitrary intensity and detuning, is treated by solving Schroedinger's equation directly for the state of the scattered field. The calculation is performed in a basis of dressed atom states, which include to all orders the coupling of the incident field to the atom. Amplitudes describing sequences of scattering events are found by a nonperturbative method. A scattered intensity spectrum, directly related to the rate of change of energy in any given scattered field mode, is constructed in terms of bilinear products of the amplitudes representing all possible sequences of photon emission, and in the steady state limit the spectrum is found to be identical to the widely quoted results of Mollow. A discussion is devoted to understanding in physical terms the various quantities appearing in the expression for the intensity spectrum.

Ballagh, R. J.↗