Half-power Diameter Research Articles

Fabrication, performance, and figure metrology of epoxy-replicated aluminum foils for hard x-ray focusing multilayer-coated segmented conical optics

We fabricated x-ray mirrors for hard x-ray (*10 keV) tele- scopes using multilayer coatings and an improved epoxy-replicated alu- minum foil (ERAF) nonvacuum technology. The ERAF optics have ;1 arcmin axial figure half-power diameter (HPD) and passed environmen- tal testing. Reflectivity measurements at 8 keV on ERAFs with and with- out multilayer coatings show a 4.4 to 4.8 A root mean square (rms) microroughness for correlation lengths <15 mm. To reduce the dominant contribution of mirror assembly and large-scale distortion in the overall telescope HPD, we designed a figure metrology system and a new mounting technique. We describe a cylindrical metrology system built for fast axial and roundness figure measurement of hard x-ray conical op- tics. These developments lower cost and improve the optics perfor- mance of the HEFT (high-energy focusing telescope) and Constellation-X missions. © 2000 Society of Photo-Optical Instrumentation Engi- neers. (S0091-3286(00)01611-1)

Supermirror hard-x-ray telescope

The practical use of a grazing x-ray telescope is demonstrated for hard-x-ray imaging as hard as 40 keV by means of a depth-graded d-spacing multilayer, a so-called supermirror. Platinum-carbon multilayers of 26 layer pairs in three blocks with a different periodic length d of 3-5 nm were designed to enhance the reflectivity in the energy range from 24 to 36 keV at a grazing angle of 0.3 deg. The multilayers were deposited on thin-replica-foil mirrors by a magnetron dc sputtering system. The reflectivity was measured to be 25%-30% in this energy range; 20 mirror shells thus deposited were assembled into the tightly nested grazing-incidence telescope. The focused hard-x-ray image was observed with a newly developed position-sensitive CdZnTe solid-state detector. The angular resolution of this telescope was found to be 2.4 arc min in the half-power diameter.

Evaluation of Enhanced High-Resolution Laser Doppler Imaging in anin VitroTube Model with the Aim of Assessing Blood Flow in Separate Microvessels

An enhanced high-resolution laser Doppler imaging (EHR-LDI) technique intended for visualization of separate microvessels was evaluated by use ofin vitroflow models. In EHR-LDI, a laser beam focused to a half-power diameter less than 40 μm successively scans the tissue under study in steps of 25 μm. Spatial blood flow variations within microvascular structures of 1.5 × 1.5 mm are rendered by 64 × 64 measurement sites. Individual microvessel diameters could be estimated and an average difference of 11 μm compared to microscopic measurements was obtained. For the flow algorithm used, the LDI output signal was found to scale linearly with average velocity (0–3.5 mm/s) when a plastic tube of inner diameter 175 μm was perfused with human blood (correlation coefficient 0.99). The LDI output signal was further found insensitive to hematocrit variations in the range 16–44%. Due to the limited laser light penetration in blood, a reduction in the LDI output signal was observed as the inner tube diameters were successively changed from 280 to 1400 μm.

Characterization of the Advanced Satellite for Cosmology and Astrophysics x-ray telescope: preflight calibration and ray tracing

The x-ray properties of multinested thin-foil mirror x-ray telescopes (XRT's) on board ASCA, the Advanced Satellite for Cosmology and Astrophysics, were fully evaluated with an x-ray pencil beam.Scanning over the telescope aperture of 35 cm in diameter with an x-ray pencil beam, we found the effective area of a set of XRT's to be 325, 200, and 113 cm(2) at energies of 1.5, 4.5, and 8.0 keV, respectively. We derive the point-spread functions (PSF's) of the XRT's by measuring the image profile at the focal plane with an x-ray CCD. The PSF is found to exhibit a sharp core concentrated within 30 arcsec and a broad wing extended to 3 arcmin in half-power diameter. We also evaluate the contribution of stray light, which is caused by the single reflection of x rays by primary or secondary mirrors and by the backside reflection of the mirrors. To obtain the characteristics of the XRT in the energy region of 0.5-10.0 keV, incorporated with the measurements at discrete energies, we develop a ray-tracing method with the telescope design parameter, the PSF, and optical constants. In particular, we obtain the optical constants around the gold-atom M shell (Au-M) absorption-edge energies by measuring the reflectivity of our mirror sample, with monochromatized x-rays in the energy range of 2.0-3.5 keV from synchrotron radiation. Taking into account the PSF's and optical constants, we find that our ray-tracing program can reproduce all these XRT performances.

The effects of large- and small-scale density structures on the radio emission from coronal streamers

The radio observations of the coronal streamers obtained using Clark Lake radioheliograph at 73.8, 50.0, and 38.5 MHz during a period of minimum activity in September 1986 are presented. Streamers appear to correlate with two prominent disk sources whose intensities fluctuated randomly. The variations in half-power diameter of the radio Sun are found to correspond with the variations in the white-light extents of the coronal streamers. It appears that the shape of the radio Sun is not a function of the phase of the solar cycle; instead it depends on the relative positions of the streamers in the corona. The observed peak brightness temperatures,T B , of the streamers are found to be very low, being ≃6 × 104 K. We compute the brightness temperature distribution along the equator by tracing the rays in the coronal plasma. The rays are deflected away by the streamers before reaching the critical density level, whereas they penetrate deeper into the coronal hole for small angles between the line of sight and the streamer axis. As a consequence, it is found that the streamers and coronal holes appear in the calculated equatorial brightness distribution as irregular brightness depressions and enhancements, respectively. The fine structures are found to disappear when the scattering due to small-scale density inhomogeneities is included in the ray-tracing calculations. The required relative level of density fluctuations, ∈1 = ΔN/N, is found to be greater than 12% to reduce the peak brightness temperature from 106 K to 6 × 104 K for all the three frequencies.

Imaging capabilities of SXT for Solar-A

The Soft X-ray Telescope (SXT) is a grazing-incidence solar X-ray telescope which will be flown on the Japanese Solar-A satellite. The Solar-A satellite, which is scheduled for launch in 1991, will carry an ensemble of instruments designed to study the Sun during the next solar sunspot maximum. The SXT will be the first high-resolution X-ray telescope since Skylab to be flown on an extended-duration mission. Measurements have been conducted to determine the focal length, point spread function, and effective area of the SXT mirror. The results indicate a half-power diameter of 4.9 arcsec and an effective area of 1.33 cm 2 at 13.3 Å. The mirror achieves high-contrast imaging with very little X-ray scattering. The telescope fwhm is 3.2 arcsec at 8.32 Å. A coaligned aspect telescope operating at visible wavelengths will permit imaging of magnetic plage or solar continuum radiation with the same plate scale as the X-ray images.

X-ray and optical profiler analysis of electroformed x-ray optics

Electroformed grazing incidence mirrors were tested with x rays and were measured with an optical profiler. Their total effective areas are ?70% of the theoretical values both for 1.5- and 6.4-keV x rays. The half-power diameters (HPDs) are ?2 min of arc at 1.5 keV. Comparing the x-ray test result with the optical measurement, we set requirements of high-frequency roughness <14 A and a midfrequency roughness <70 A for a HPD <1.5 min of arc at 7 keV. We also present a design of the mirror array telescope for high energies (MARTHE) which has a total effective area of ~1000 cm(2) for 7- keV x rays.

X-ray mirror assessment with optical light

The imaging capability of a thin foil x-ray mirror has been examined with optical light, using a laser beam and a wide optical parallel beam. These measurements reveal that (1) image broadening due to millimeter scale waviness (orange peel) of the aluminum substrate, partly intrinsic to the foil and partly caused during the foil treatment, is 1.2-min of arc half-power diameter (HPD) in two reflections; (2) slope errors due to foil shaping and misalignment cause broadening of 1.6-2.0-min of arc HPD; (3) total broadening is ~3-min of arc HPD, which is consistent with the broadening of 2.6-min of arc HPD measured with x rays.

The internal structure of the dust shell of Eta Carinae deduced from six channel 8-13 micron mapping

view Abstract Citations (53) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Internal Structure of the Dust Shell of Eta Carinae Deduced from Six Channel 8--13 Micron Mapping Hackwell, John A. ; Gehrz, Robert D. ; Grasdalen, Gary L. Abstract The authors have used a six channel infrared photometer to map η Carinae at 8.1, 8.9, 10.4, 11.3, 12.2, and 13.1 μm. The half-power diameter of the beam on the CTIO 4 m telescope was 1arcsec.7. The maps resolve a "cool" double source in the core and show the presence of a third "hot" source which dominates the core at 8.1 μm. The homunculus has a sharp edge and is the same size (12arcsec×18arcsec) at all wavelengths between 8 and 13 μm. The authors also see bipolar "horns" in the homunculus which are most apparent at the longest wavelengths. A straightforward silicate emission model has been fitted to the six channel spectra at each position in the infrared nebula. Publication: The Astrophysical Journal Pub Date: December 1986 DOI: 10.1086/164779 Bibcode: 1986ApJ...311..380H Keywords: Cosmic Dust; Infrared Sources (Astronomy); Novae; Image Enhancement; Maximum Entropy Method; Optical Thickness; Silicates; Astrophysics; INFRARED: SOURCES; INTERSTELLAR: GRAINS; NEBULAE: INDIVIDUAL NAME: ETA CARINAE full text sources ADS | data products SIMBAD (1)

VLA Observations of Ag-Pegasi R-Aquarii and R-Leonis at 6-CENTIMETERS

view Abstract Citations (11) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS VLA observations of AG Peg, R Aqr, and R Leo at 6 cm. Ghigo, F. D. ; Cohen, N. L. Abstract AG Pegasi's nebulosity was found to have a half-power diameter of about 1" or 1016 cm. Its 6 cm flux density increased from 6.2 mJy in 1979 January to 8.0 mJy in 1980 May. Including previous radio observations, we estimate a spectral index of α ≍ 0.7, suggestive of emission from a mass outflow. However, theoretical mass outflow models predict an angular size somewhat smaller than observed. Perhaps a nonspherically symmetric mass-loss model is required. R Aquarii was unresolved (θ < 2"), and there is no obvious correlation between its radio and optical variations. A stringent upper limit of 0.7 mJy for R Leonis is consistent with the possibility that nonsymbiotic Miras are less likely to have radio continuum emission. Publication: The Astrophysical Journal Pub Date: May 1981 DOI: 10.1086/158875 Bibcode: 1981ApJ...245..988G full text sources ADS | data products SIMBAD (3)

Observations of the quiet Sun at meter and decameter wavelengths

The new TeePee Tee array of the Clark Lake Radio Observatory has been used to observe the quiet Sun at 121.5, 73.8 and 26.3 MHz. The equatorial brightness distributions at all three frequencies, and the polar brightness distributions at the two higher ones have been measured. From the observed total fluxes and half-power diameters we have derived the peak brightness temperatures of the solar disk as well as of some sources of the slowly varying component.

The nature of the broad molecular line emission at the Kleinmann-Low nebula

view Abstract Citations (220) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The nature of the broad molecular line emission at the Kleinmann-Low nebula. Kwan, J. ; Scoville, N. Abstract We have mapped the high-velocity emission in the wings of the CO line at the Kleinmann-Low infrared nebula. The half-power diameter is found to be 80 arcseconds. Upon analysis of the observed intensity profiles and the variations in angular size at different velocities, we conclude that a differentially expanding envelope, possibly the result of an explosive event, is the most likely explanation. The kinetic energy in the flow is 4 times 10 to the 47th ergs, based on a numerical model of the CO emission. The recently observed v = 1 to 0 radiation of H2 would arise from the shock front preceding the expanding gas. Publication: The Astrophysical Journal Pub Date: November 1976 DOI: 10.1086/182298 Bibcode: 1976ApJ...210L..39K Keywords: Carbon Monoxide; Infrared Spectra; Interstellar Radiation; Molecular Spectra; Nebulae; Astronomical Spectroscopy; Gas Expansion; Hydrogen Clouds; Kinetic Energy; Line Shape; Shock Fronts; Spectral Line Width; Astrophysics full text sources ADS | data products SIMBAD (1)

CW self-focusing and self-trapping of light in sodium vapor

We report steady-state self-focusing, self-trapping, and self-defocusing of a cw dye laser beam in sodium vapor for frequencies within several Doppler widths of the $D$-line resonance transitions. We measured the variation of the beam profile as the light propagates through the vapor. We observed a 20-mW beam self-trapped in a 12-cm-long filament having a half-power diameter of 70 \ensuremath{\mu}m.

Cw Self-Focusing and Self-Trapping of Light in Sodium Vapor

We report steady-state self-focusing, self-trapping, and self-defocusing of a cw dye laser beam in sodium vapor for frequencies within several Doppler widths of the $D$-line resonance transitions. We measured the variation of the beam profile as the light propagates through the vapor. We observed a 20-mW beam self-trapped in a 12-cm-long filament having a half-power diameter of 70 \ensuremath{\mu}m.

Direct comparison of thermal and magnetic profiles in ``Curie point'' writing on MnGaGe films

Measurements have been made of both the real-time temperature profile and the steady-state magnetization profile achieved in a film of MnGaGe as a result of ``Curie point'' writing with a GaAs laser pulse. A HeNe laser probe having a half-power diameter of 1 μ was used to measure both profiles. Temperature was measured during and after application of the heat pulse by relating the time-dependent transmission change of the heated area of the film to the temperature-calibrated shift of the absorption edge of MnGaGe. Magnetization information was obtained by measuring the Faraday rotation within the written area after the film had cooled to ambient. A comparison of the two profiles indicates that (a) magnetization reversal occurs at temperatures well below the Curie point, even in the absence of an external bias field, and (b) the critical temperature required for reversal increases with an increase in the size of the heated area. Both results can be explained qualitatively by local demagnetization effects.

Internal Structures and Spectra of 3c 273 from Lunar Occultations

Seven observations (disappearance or reappearance) were taken at five frequencies, 234, 256, 405, 735, and 2693 Mc, up to four frequencies simultaneously. The positions of the components agree within 0.8 with those of Moffet obtained by the same method; component B (QSS) agrees within 0.7 with the optical position of Jefferys. The average half-power diameter of both components is about 2'S at all frequencies. Both components are considerably elongated along their connecting axis; especially A (end of jet) is just a straight, narrow line. The structure of both components depends strongly on frequency. Component B is a single, strong source about 2" wide at 2695 Mc; at 735 Mc it shows a halo about 6" long, and a core &lt;1" large (with 30 per cent of the flux); the core is less pronounced at 405 Mc; but at the lower frequencies component B shows a deep minimum right at the center. Component A seems to have a central dip at 2695 Mc; at 735 Mc it has a halo about 10 long and a core &lt;1" large (with 30 per cent of the flux); and at the lower frequencies component A has a half-power length of about 4 but shows a faint, very flat extension about 23" long, almost touching the outer part of B. The spectrum of A is a straight line with spectral index a = -0.68 + 008. A straight line holds for B only above 400 Mc, with a = +0.25 + 008 with a cutoff to lower frequencies. Each component is then divided into an outer part and a central part 4'.'8 long. The central spectrum of A still is about straight with a = -082 + 0 22 while the low-frequency cutoff for the center of B is very steep. Both outer parts are very similar and give a = -0.43 + 0.20.