Green Line Emission Research Articles

Laser characteristics at 1535 nm and thermal effects of an Er:Yb phosphate glass microchip pumped by Ti:sapphire laser

An Er:Yb codoped phosphate glass microchip laser has been studied under pumping with a Ti:sapphire laser ranging from 945 to 990 nm. The characteristics (threshold, slope efficiency) are first described for an optimized laser. The gain spectrum is calculated for the transition 4 I 13/2→ 4 I 15/2 around 1535 nm from fundamental spectroscopic data and from experimental results. Red-shift effect on the frequency of a single mode is experimentally observed when the pump power is increased, originating from thermal effects. Temperature inside the microchip cavity and thermal expansion coefficient were determined by employing the intensity ratio of two green upconversion emission line centered at 530 and 554 nm, respectively, which quantitatively explain this red shift.

Longitudinal variations of green line emission rates observed by WINDII at altitudes 90– [formula omitted] during 1991–1996

Longitudinal variations in green line airglow are investigated. The volume emission rate data used for the analysis are taken by Wind-Imaging Interferometer (WINDII) at latitudes 70°S–70°N and altitudes 90– 120 km in December/January and March/April of 1991–1996. Relatively stable or stationary patterns, which persist from year to year, are found to exist at fixed local times during solstice and equinox. In general, the nightglow exhibits zonal wavenumber one and two variations in the southern and northern latitudes around 35°, respectively. The dayglow displays a wavenumber two variation near the equator, with a tendency towards 10°S–20°S for the solstitial period. All structures are seen to extend over 10° or more of latitude. The emission rates vary significantly, changing by a factor 2 or more at the minima and maxima of the wave structures. Primary maxima are around ∼180°E–240°E for the nightglow, and ∼300°E–360°E for the dayglow, while secondary maxima are near ∼90°–120°E for both airglows. Their magnitudes also show systematic decrease by a factor of 3 from year 1991 to 1996, perhaps due to decreases in solar activity and tidal amplitude. The existence of a stationary planetary wave structure suggests the importance of coupling processes between the mesopause and the earth (or lower atmosphere) in understanding the airglow variations, in addition to the well-known solar-driven photochemistry.

The eruptive events on September 30, 1998: 1. The jet

The jet on September 30, 1998, is part of a complex event that involved also other eruptive phenomena. Changes in the coronal magnetic field topology were observed during the ejection of the jet, as deduced from the Fe XIV green line emission. The whole event was well observed by both the H‐Alpha Solar Telescope for Argentina (HASTA) and the Mirror Coronagraph for Argentina (MICA), which are installed in the German‐Argentinean Solar Observatory at El Leoncito, Argentina. The Soft X‐ray Telescope (SXT) on board Yohkoh also observed the jet. In this work, observations of the first part of this complex event showing the evolution of the jet and release of blobs are presented. Certain features observed are interpreted as signatures of a magnetic reconnection process in the region. We conclude that existing theoretical and phenomenological models based on magnetic reconnection mechanisms could explain our observations, which span three temperature regimes far apart from each other.

Analysis of the green-line corona polarization

The green-line corona polarization data obtained by J. Sfkora (Slovak Republic) during the solar eclipse of 11 July, 1991, have been analyzed. In the course of the analysis we came into a difficulty associated with the fact that the observed direction of the polarization vector did not agree with that inferred from the generally accepted theory. Therefore, not relying on calculations of the intensity and polarization of light scattered by Fe XIV ions in a medium with a magnetic field, we suggest an interpretation based on the assumption of pre-defined polarization of the scattered green-line emission Pph (i.e. in the absence of electron collisions). This approach allows us to estimate the contribution of scattering to the total line intensity and to obtain some new information concerning the physical conditions in the line-emission regions. Besides, simultaneous examination of line polarization and white-light coronal data makes it possible to divide the total white-light emission into two components, one of which arises in the line-emission regions, and the other outside the temperature range corresponding to the given ion.

A case study of HF radar spectra and 630.0 nm auroral emission in the pre-midnight sector

Abstract. A comparison of HF radar backscatter observed by the CUTLASS Finland radar, meridian scanning photometer data from Longyearbyen, magnetic field variations from IMAGE stations, and particle precipitation measured by the DMSP F12 spacecraft is presented. The interval under discussion occurred in the pre-midnight local time sector, during a period of weakly northward interplanetary magnetic field. A region of HF backscatter, typically 8 degrees wide, occurred in the field of view of the CUTLASS Finland radar. A well defined gradient in the spectral width parameter was present, with mainly low (< 200 m s - 1 ) spectral widths in the lower latitude part of the scatter and predominantly large (> 200 ms - 1 ) spectral widths in the higher latitude part. The relationship between the spectral width and the red line (630.0 nm) emission measured by the meridian scanning photometer is considered. The poleward border of the red line emission, which has, in the past, been proposed as being representative of the polar cap boundary, was co-located to within 1° of magnetic latitude with the gradient in spectral width for part of the interval. Statistically, large spectral widths occurred poleward of the red line emission, while small spectral widths occurred within or equatorward of the red line emission. Near simultaneous DMSP particle observations in the 20 eV to 20 keV range indicate that the poleward border of the red line emission and the gradient in spectral width occurred at the same latitude as the transition from auroral oval to polar rain particle energies. We conclude that the large spectral widths were not caused by particle precipitation associated with the auroral oval. There were two periods of special interest when the relationship between the red line and the spectral width broke down. The first of these happened during enhanced red line and green line (557.7 nm) emission, with a drop out of the radar scatter and an enhanced, narrow westward electrojet. We conclude that this event was a magnetospheric substorm occurring at much higher than usual latitudes. The second period of special interest happened when equatorward moving bands of large spectral width occurred within the region of scatter. Up to 4 of these bands were present during an interval of 100 minutes. Associated with these narrow bands of large spectral width were narrow channels of enhanced westward ion velocities. We conclude that these equatorward moving bands of large spectral width may be related to reconnection processes in the tail. The observations demonstrate that the tail continues to be active even under low solar wind energy input conditions. Furthermore, we conclude that the gradient in the spectral width may be used as a proxy for the polar cap boundary, but only with extreme caution.Key words. Ionosphere (ionosphere-magnetosphere inter-actions; polar ionosphere) – Magnetospheric physics (storms and substorms)

Discovery of the atomic oxygen green line in the Venus night airglow.

Green line emission at 557.7 nanometers arising from the O(1S - 1D) transition of atomic oxygen has been observed on the nightside of Venus with HIRES, the echelle spectrograph on the W. M. Keck I 10-meter telescope. We also observe optical emissions of molecular oxygen, consistent with the spectra from the Venera orbiters, but our green line intensity is so high that we cannot explain how it could be inconspicuous in the Venera spectra. An upper limit for the intensity of the O(1D - 3P) oxygen red line at 630 nanometers has also been obtained. The large green/red ratio indicates that the source is not associated with the Venus ionosphere. An important conclusion is that observation of the green line in a planetary atmosphere is not an indicator of an atmosphere rich in molecular oxygen.

Long-term cyclic variations of prominences, green and red coronae over solar cycles

Long-term cyclic variations in the distribution of prominences and intensities of green (530.3 nm) and red (637.4 nm) coronal emission lines over solar cycles 18–23 are presented. Polar prominence branches will reach the poles at different epochs in cycle 23: the north branch at the beginning in 2002 and the south branch a year later (2003), respectively. The local maxima of intensities in the green line show both poleward- and equatorward-migrating branches. The poleward branches will reach the poles around cycle maxima like prominences, while the equatorward branches show a duration of 18 years and will end in cycle minima (2007). The red corona shows mostly equatorward branches. The possibility that these branches begin to develop at high latitudes in the preceding cycles cannot be excluded.

Contribution and Properties of the Green- and Red-Line Coronal Loops in the K-Corona

A set of high-resolution images of corona obtained during the total solar eclipse on 1991 July 11, was carefully analyzed to investigate the properties of the loop structures observed in the green (530.3 nm) and red (637.4 nm) emission lines and in the continuum. With the help of a structure-enhancement algorithm, we have quantitatively shown that: (1) The green- and red-line loops are quite separately distributed in space. (2) For most structures seen in the continuum in the active-region corona, components can be identified in the green or red line. (3) In the innermost corona, structures in the red-line tend to contribute more to the total column density than the green-line structures. We present two schematic models to explain the spatial relation of the green-line, the red-line, and the continuum loops. Next, we studied individual loops in the green and red lines, and derive that their electron densities are almost the same. We also propose a method to determine the ‘background contribution’ of the green and red lines to the total column density derived from the continuum intensity. It is found that the total column density in the analyzed region can be reasonably explained by a mixture of the 530.3 nm component with a line-of-sight length comparable to the size of the active region, and the 637.4 nm component, which tends to concentrate in loop structures. We thereby conclude that the observed corona is well explained by a plasma of temperatures ranging from 2 MK to 1 MK.

Ionospheric signatures of magnetospheric boundaries in the post-noon sector

Abstract. Spatial structures in ionospheric electron density revealed in a tomographic image have been identified with auroral forms and related to their sources in precipitating particles observed by DMSP satellites. The observations of plasma enhancements relate to discrete auroral arcs seen in the post-noon sector, identified by both red- and green-line emissions measured by a meridional scanning photometer. The features lie within a very narrow latitudinal band on L-shells where the satellite detectors observed electron precipitation classified as from the boundary plasma sheet (BPS). The harder particles are identified with an E-region structure, while further north the precipitation is softer, resulting in a localised F-layer blob and 630.0 nm emissions. A steep gradient in plasma density represent a signature in the ionosphere of the central plasma sheet (CPS)/BPS boundary. A transition to a less-structured F-layer is found on crossing the convection reversal boundary..Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; polar ionosphere)

Long-term Cyclic Variations of Prominences, Green and Red Coronae over Solar Cycles

AbstractLong-term cyclic variations in the distribution of prominences and intensities of green (530.3 nm) and red (637.4 nm) coronal emission lines over solar cycles 18–23 are presented. Polar prominence branches will reach the poles at different epochs in cycle 23: the north branch at the beginning in 2002 and the south branch a year later (2003), respectively. The local maxima of intensities in the green line show both poleward- and equatorward-migrating branches. The poleward branches will reach the poles around cycle maxima like prominences, while the equatorward branches show a duration of 18 years and will end in cycle minima (2007). The red corona shows mostly equatorward branches. The possibility that these branches begin to develop at high latitudes in the preceding cycles cannot be excluded.

The Enhanced Coronal Green Line Intensity and the Magnetic Field Gradients

Extended abstractRamesh, Nagabhushana and Varghese (1999) have shown that the green line intensity enhancement does not depend entirely on the strength of the underlying spot magnetic field though the coronal intensity enhanced feature is almost sure to occur at the locations of sunspots with strong magnetic fields and at the locations of plages having larger areas. Presented here are the results of an analysis of intensity of green line emission and the active region magnetic signatures as seen in Stanford magnetograms.The data base used in this study consisted of homogeneous data set (HDS) of 5303 Å green coronal intensity measured at position angle intervals of 5° on any given day from several stations (see Rybanský, 1975) and brought down to the common scale of Lomnicky Štit. Daily maps of sunspots, and Ca plages are then superposed on the green line intensity maps of the corresponding day. Resultant composite maps are then compared with the Stanford magnetograms published inSolar Geophysical Data.

Common-volume measurements of mesospheric winds using radar and optical instruments: 1. Comparison of observations

The Millstone Hill incoherent scatter radar (42.6°N, 71.5°W) and the nearby Durham meteor wind radar (43.1°N, 70.9°W) have been used to study the structure of the winds in the mesosphere and lower thermosphere and to investigate the propagation of tidal components from the mesosphere into the lower thermosphere. In general, good agreement is found between the tidal wind amplitudes and phases determined by the two radars, but occasionally, some discontinuities have been observed in the vertical structure of the tidal components in the 90–110 km region. In order to validate the accuracy of the two techniques and the methodologies used in determining neutral winds, two common-volume experiments were conducted in 1996 and 1997 in which the two radar beams were overlayed at an altitude of 100 km. The horizontal components of the measured radar line-of-sight velocities during day-time periods were then compared at the overlapping altitudes of 95–100 km. Night-time measurements were also made using a Fabry–Perot Interferometer co-located with the radar at Millstone Hill which observed the Doppler shift of the atomic oxygen green line emission in the mesosphere. Good overall agreement is found between the instruments within the statistical uncertainties of the measurement techniques, although some differences have been found that are explained by consideration of the data statistics, the exact overlap of common volume within the different beam sizes, and the presence of altitude gradients and small scale irregularities in the sampled volumes of the atmosphere.

The dynamic cusp aurora on 30 November 1997: response to southward turning of the IMF

Abstract. We document the detailed dynamics of the dayside aurora in the \\sim1200-1600 MLT sector in response to a sharp southward turning of the interplanetary magnetic field (IMF) under negative IMF By conditions. Features not documented in previous work are elucidated by using two meridan scanning photometers (separated by 2 h) and an all-sky auroral imager in Ny Ålesund, Svalbard (75.5°MLAT) in combination with magnetograms from stations on Svalbard, covering the latitude range 71°75°MLAT. The initial auroral response may be divided into three phases consisting of: (1) intensification of both the red (630.0 nm) and green (557.7 nm) line emissions in the cusp aurora near 1200 MLT and ~100 km equatorward shift of its equatorward boundary, at ~75°MLAT, (2) eastward and poleward expansions of the cusp aurora, reaching the 1430 MLT meridian after 5-6 min, and (3) east-west expansion of the higher-latitude aurora (at ~77°78°MLAT) in the postnoon sector. The associated magnetic disturbance is characterized by an initial positive deflection of the X-component at stations located 100-400 km south of the aurora, corresponding to enhanced Sunward return flow associated with the merging convection cell in the post-noon sector. The sequence of partly overlapping poleward moving auroral forms (PMAFs) during the first 15 min, accompanied by corresponding pulsations in the convection current, was followed by a strong westward contraction of the cusp aurora when the ground magnetograms indicated a temporary return to the pre-onset level. These observations are discussed in relation to the Cowley-Lockwood model of ionospheric response to pulsed magnetopause reconnection.Key words. Mangetospheric physics (magnetopause · cusp and boundary layers; solar wind-magnetosphere interactions; auroral phenomena)

Visible and Infrared Rare-Earth Activated Electroluminescence from Erbium Doped GaN

Room temperature visible and IR light electroluminescence (EL) has been obtained from Er-doped GaN Schottky barrier diodes. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources (for Ga and Er) and a plasma source for N2. Transparent contacts utilizing indium tin oxide were employed. Strong green light emission was observed under reverse bias due to electron impact excitation of the Er atoms. Weaker emission was present under forward bias. The emission spectrum consists of two narrow green lines at 537 and 558 nm and minor peaks at 413, 461, 665, and 706 nm. There is also emission at 1000 nm and 1540 nm in the IR. The green emission lines have been identified as Er transitions from the 2H11/2 and 4S3/2 levels to the 4I15/2 ground state. The IR emission lines have been identified as transitions from the 4I11/2 and 4I13/2 levels to the 4I15/2 ground state. EL intensity for visible and IR light has a sub-unity power law dependence on bias current. An external quantum efficiency of 0.1% has also been demonstrated under a reverse bias current of 3.85 mA.

The Effect of Mass Motions Inside the Coronal Loops on Emission Line Profiles

The observed green coronal emission line profiles have been often found to have multi-components. Further examinations reveal that the occurrence of multi-components in line profiles is related to the solar cycle variations as well as the activity of the coronal region. The spatial correspondence between the intense loops in active regions and strong multi-components in line profiles suggests that the presence of loops affects the line shapes. The emission line profiles have been found to be fitted well with single or multi-Gaussians with line-of-sight velocities up to 70 km s−1. A simple radiative transfer model of coronal emission line profiles is developed which shows that coronal loops with mass motions inside may give rise to multi-components in line profiles. The effects of loop parameters such as electron density, flow velocity and kinetic temperature and the line-of-sight variations are studied. It is found that line profiles strongly reflect the physical conditions inside the loop.

The morphology of oxygen greenline dayglow emission

Abstract. In this study, the morphology of the oxygen greenline dayglow emission is presented. The volume emission rate profiles are obtained by using Solomon's glow model. The glow model is updated in terms of recent cross sections, reaction rate coefficients and quantum yield of greenline emission. Throughout most of the thermosphere the modelled and observed emission rates are in reasonably good agreement. In the region between 98 and 120 km, the modelled emission rates are substantially higher (about a factor of 1.7) than the observed emission rates. This discrepancy is discussed in terms of scaling of solar fluxes which accounts the variation of solar activity for the day on which calculations are made. The modelled morphology of greenline emission is compared with those cases where WINDII data is available. The modelled and observed morphology is in reasonably good agreement at most of the latitudes above 120 km. In the mesosphere the qualitative nature of morphology is very similar to those of WINDII observation except the modelled emission rates are about a factor of 1.7 higher than the observed emission rates.Keywords. Ionosphere (ion chemistry and composition; modeling and forecasting; solar radiation and cosmic ray effects).

Green electroluminescence from Er-doped GaN Schottky barrier diodes

Visible light electroluminescence (EL) has been obtained from Er-doped GaN Schottky barrier diodes. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources (for Ga, and Er) and a plasma source for N2. Al was utilized for both the Schottky (small-area) and ground (large-area) electrodes. Strong green light emission was observed under reverse bias, with weaker emission present under forward bias. The emission spectrum consists of two narrow green lines at 537 and 558 nm and minor peaks at 413 and at 666/672 nm. The green emission lines have been identified as Er transitions from the H11/22 and S3/24 levels to the I15/24 ground state and the blue and red peaks as the H9/22 and F9/24 Er transitions to the same ground state. The reverse bias EL intensity was found to increase linearly with bias current.

Spectroscopy and laser characteristics of copper-vapor-laser pumped Pyrromethene-556 and Pyrromethene-567 dye solutions

We measured the basic optical properties of Pyrromethene-567 (P567) and Pyrromethene-556 (P556) dye solutions that are relevant to their application as dye lasers. The fluorescence spectra of methanol solutions show mirror images in relation to the absorption spectra, with Stokes shifts of 29.5 and 37.5 nm, respectively, for the two dyes. The central fluorescence peaks were at 546 and 535 nm, with widths of ~40 and ~50 nm (FWHM). The quantum yields were 97% ? 5% and 78% ? 5% for P567 and P556, respectively. Fluorescence lifetimes of 6.0 ? 0.2 ns were obtained for both dyes in methanol. Laser action, obtained by pumping with the green emission line (510.6 nm) from a copper-vapor laser, was measured in a Hänsch-type cavity. Tunability ranged from 531 to 590 nm for P567 and from 522 to 590 nm for P556. Lasing thresholds were ~0.27 and ~0.16 mJ/pulse, with 25% and 27% slope efficiencies for P567 and P556, respectively. Spectroscopy and lasing were studied in other solvents as well.

Infrared to visible frequency upconversion in erbium-doped Ga 2S 3–La 2O 3 chalcogenide glass

Infrared to visible frequency upconversion in an erbium-doped lanthanum-oxide chalcogenide glass excited at 1.06 μm, is reported for the first time. Intense green upconversion emission lines at 525 and 550 nm of the thermally coupled excited state levels 2 H 11/2 and 4 S 3/2, respectively, is observed. A much lower intensity emission band around 670 nm corresponding to the 4 F 9/2– 4 I 15/2 transition, is also observed. Two-photon absorption and phonon-assisted energy transfer account for the upconversion excitation mechanism.

Visible and Infrared Rare-Earth Activated Electroluminescence From Erbium Doped GaN

AbstractRoom temperature visible and IR light electroluminescence (EL) has been obtained from Er-doped GaN Schottky barrier diodes. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources (for Ga and Er) and a plasma source for N2. Transparent contacts utilizing indium tin oxide were employed. Strong green light emission was observed under reverse bias due to electron impact excitation of the Er atoms. Weaker emission was present under forward bias. The emission spectrum consists of two narrow green lines at 537 and 558 nm and minor peaks at 413, 461, 665, and 706 nm. There is also emission at 1000 nm and 1540 nm in the IR. The green emission lines have been identified as Er transitions from the 2H11/2 and 4S3/2 levels to the 4I15/2 ground state. The IR emission lines have been identified as transitions from the 4I13/2 and 4I13/2 levels to the 4I15/2 ground state. EL intensity for visible and IR light has a sub-unity power law dependence on bias current. An external quantum efficiency of 0.1% has also been demonstrated under a reverse bias current of 3.85 mA.