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Lindsey, C.

Publications and source records attributed to Lindsey, C..

33 records · Page 2
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NASA NTRS1984

Observations of the brightness profile of the sun in the 30-200 micron continuum

The brightness profile of the quiet sun in broad continuum passbands centered at 30, 50, 100, and 200 microns was observed with a resolution of 2 arcmin. Weak radial darkening was seen at all four wavelengths near disk center. This reverses to brightening toward the limb in the 100 and 200 micron continuum. Radial darkening at 100 and 200 microns is not expected from smooth model chromospheres consistent with absolute brightness measurements. These results do not support a homogeneous model of the low chromosphere, where the temperature reversal occurs.

Lindsey, C.↗
NASA NTRS1984

Coupled parallel waveguide semiconductor laser

The operation of a new type of tunable laser, where the two separately controlled individual lasers are placed vertically in parallel, has been demonstrated. One of the cavities ('control' cavity) is operated below threshold and assists the longitudinal mode selection and tuning of the other laser. With a minor modification, the same device can operate as an independent two-wavelength laser source.

Katz, J.↗
NASA NTRS1984

Coupling mechanism of gain-guided integrated semiconductor laser arrays

It is shown that a gain-guided laser array couples via propagating fields rather than the evanescent mode coupling typically responsible for directional coupling in passive (directional couplers) and active (laser array) devices. It is shown that these phase-locked modes exhibit an interference pattern, in the junction plane, which arises from the curvature of the phase fronts of optical fields of the interacting lasers. The experimental results are interpreted with the aid of a simple theoretical model, and the effect of the observed mode pattern on the coupling of gain-guided lasers is discussed.

Kapon, E.↗
NASA NTRS1984

Solar limb brightening at 820 microns

The sun in 820 micron radiation is mapped, and strong radial brightening of the intensity profile is found. The east and west limbs show an intensity excess of about twice that of the quiet north and south limbs. This may be attributable to active regions near the east and west limbs. The radial brightening observed is as strong as that observed by others at 1.3 mm, and much stronger than that observed at 350 microns by still others. A strong general increase in gradual radial brightening with wavelength longward of 350 microns is thus indicated, and this is attributed to variations in the character of chromospheric fine structure above the temperature minimum region.

Lindsey, C.↗
NASA NTRS1983

Phase-locked semiconductor laser array with separate contacts

A new monolithic phase-locked semiconductor laser array has been fabricated. Employing two-level metallization, each of the eight elements in the array has a separate contact, thus making it possible to compensate for device nonuniformities and control the near-field and far-field patterns. Threshold currents are approximately 60 mA for each 5-micron-wide laser in the array. Phase locking has been observed via the narrowing of the far-field pattern. Experimental results are compared to those obtained from the same arrays operated with all the lasers connected in parallel.

Katz, J.↗
NASA NTRS1983

Control of mutual phase locking of monolithically integrated semiconductor lasers

The degree of phase locking between the individual laser apertures is the major issue in phase-locked laser arrays. A description is presented of a series of experiments in which the mutual coherence of two laser apertures is characterized by measuring the visibility of the far-field interference fringes. Attention is given to an approach which makes it possible to control continuously the degree of coherence by means of a separate contact configuration. An investigation was conducted of the far-field radiation patterns of pairs of lasers obtained under various conditions. The results of the present study demonstrate the feasibility of controlling the mutual phase locking between semiconductor lasers by varying the gain distribution between their pumped stripes.

Kapon, E.↗
NASA NTRS1983

Far-field distributions of semiconductor phase-locked arrays with multiple contacts

Experimental results on far-field patterns of semiconductor laser arrays with multiple contacts are reported. It is found that, by tailoring the distribution of the currents through the array elements, narrow single-lobe patterns, which are more useful in most applications, can be obtained from arrays that usually operate in a double-lobe mode. A diffraction-limited 1.8 deg-wide far field pattern was obtained from a three-element array.

Katz, J.↗
NASA NTRS1982

Submillimeter extensions of the solar limb determined from observations of the total eclipse of 1981 July 31

First results are presented of observations of a lunar occultation of the solar limb made from the Kuiper Airborne Observatory in the 30 micrometr, 50 micrometer, 100 micrometer, and 200 micrometer continuum during the total solar eclipse of 1981 July 31. The solar limb was extended at the longer wavelengths up to 1000 km higher than predicted from smooth plane-parallel chromospheric models. Results at both second and third contact show the infrared limb extensions to be approximately 0".8, 1"5, 2".5 and 3".0 above the visible limb in the observed bands, respectively. A possible interpretation proposes chromospheric fine structure inhomogeneities of greater density than presently incorporated in models of the middle chromosphere.

Lindsey, C.↗
NASA NTRS1981

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.↗
NASA NTRS1981

Solar limb brightening at 350 microns

The NASA Infrared Telescope Facility at Mauna Kea was used to observe the intensity profile of the quiet solar limb in the 300-400 micron continuum. A significant resolved brightening of several percent over the outer 60 arcsec of the solar limb in this band is found. However, the magnitude of the brightening is considerably less than that indicated by earlier observations of a total solar eclipse in integrated sun-moon radiation by Beckman, Lesurf, and Ross (1975) in the 1.2 mm continuum. More recent ground-based observations indicate that the magnitude of solar limb brightening at 800 microns and at 1.3 mm is stronger than that at 350 microns. This may be regarded as an indication that the hot material which produces the brightening at the extreme limb, thought to consist in part of chromospheric spicules, is optically thin in the 350 micron continuum.

Lindsey, C.↗
NASA NTRS1981

Far-infrared continuum observations of solar faculae

New observations of photospheric faculae in the far-infrared (10-25 micron wavelength) continuum are presented. Two-beam linear scans with 10 arcsec and 20 arcsec resolution were used to compile statistics on infrared continuum emission from faculae surrounding sunspots. The infrared facular excess above the quiet sun continuum is found to be much smaller than that predicted by plane parallel photospheric models constructed from Mg II h and k line wing observations. It is proposed that the discrepancy results from unresolved granular structure in which the facular granules occupy only about 0.1 of the resolved surface area in the low photosphere.

Lindsey, C.↗
NASA NTRS1979

Infrared continuum observations of the solar atmosphere

The far-infrared wavelengths (10 microns to 1 mm) were used to study the spatial and temporal structure of the solar atmosphere. Observational results were obtained on flares, faculae, sunspots, and on the center-to-limb intensity distribution, as well as on time variability within these regions. A program of precise monitoring of slow variations in the integrated solar luminosity was shown to be feasible, and initial steps to implement observations were completed.

Hudson, H.↗
NASA NTRS1977

Study of effects of space power satellites on life support functions of the earth's magnetosphere

The effects of the Satellite Solar Power System (SSPS) on the life support functions of the earth's magnetosphere were investigated. Topics considered include: (1) thruster effluent effects on the magnetosphere; (2) biological consequences of SSPS reflected light; (3) impact on earth bound astronomy; (4) catastrophic failure and debris; (5) satellite induced processes; and (6) microwave power transmission. Several impacts are identified and recommendations for further studies are provided.

Douglas, M.↗
NASA NTRS1976

Solar limb brightening in submillimeter wavelengths

Differential two-beam scans of the sun in submillimeter wavelengths (350 microns to 1 millimeter) indicate limb brightening approaching 1 percent when the cosine of the angle from the normal equals 0.60. The observations also show considerable chromospheric structure, both in active and quiet regions, but with less relative amplitude than at millimeter and centimeter wavelengths. The limited angular resolution of the observing system, together with photometric errors due to fluctuating atmospheric transparency, make the brightness profile of the extreme limb uncertain. The observed degree of limb brightening is considerably less than that consistent with spherically symmetric model atmospheres based on continuum brightness-temperature measurements. The suppression of limb brightening suggests the existence of irregular granular structure with both horizontal and vertical characteristic sizes of the order of 1500 km. High-resolution images in the wings of the K-line show granular structure of about this horizontal scale.

Lindsey, C.↗