Linewidth Measurements Research Articles

THREE-DIMENSIONAL STEREOSCOPIC ANALYSIS OF A CORONAL MASS EJECTION AND COMPARISON WITH UV SPECTROSCOPIC DATA

A three-dimensional (3D) reconstruction of the 2007 May 20 partial-halo coronal mass ejection (CME) has been made using STEREO/EUVI and STEREO/COR1 coronagraphic images. The trajectory and kinematics of the erupting filament have been derived from Extreme Ultraviolet Imager (EUVI) image pairs with the "tie-pointing" triangulation technique, while the polarization ratio technique has been applied to COR1 data to determine the average position and depth of the CME front along the line of sight. This 3D geometrical information has been combined for the first time with spectroscopic measurements of the O vi λλ1031.91, 1037.61 line profiles made with the Ultraviolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory. Comparison between the prominence trajectory extrapolated at the altitude of UVCS observations and the core transit time measured from UVCS data made possible a firm identification of the CME core observed in white light and UV with the prominence plasma expelled during the CME. Results on the 3D structure of the CME front have been used to calculate synthetic spectral profiles of the O vi λ1031.91 line expected along the UVCS slit, in an attempt to reproduce the measured line widths. Observed line widths can be reproduced within the uncertainties only in the peripheral part of the CME front; at the front center, where the distance of the emitting plasma from the plane of the sky is greater, synthetic widths turn out to be ∼25% lower than the measured ones. This provides strong evidence of line broadening due to plasma heating mechanisms in addition to bulk expansion of the emitting volume.

Synthesis, dynamic properties and electrochemical stability of organic-inorganic hybrid polymer electrolytes with double core branched structures based on polyether, cyanuric chloride and alkoxysilane

A new organic-inorganic solid hybrid electrolyte based on 2,4,6-trichloro-1,3,5-triazine, triblock co-polymer poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether), poly(ethylene glycol) diglycidyl ether, and 3-(glycidyloxypropyl)trimethoxysilane doped with LiClO4 salt is synthesized by a sol-gel process. Fourier transform infrared spectroscopy and 13C NMR results reveal the successful synthesis of the organic-inorganic hybrid electrolyte. The conductivity of the hybrid electrolyte follows a VTF (Vogel-Tamman-Fulcher)-like behavior, implying that the diffusion of charge carriers is assisted by the segmental motions of polymer chains. The Li-ion mobility is determined from 7Li static NMR linewidth and diffusion coefficient measurements; both are correlated with their ionic conductivities. The maximum ionic conductivity of 9.5×10−5Scm−1 at 30°C is obtained for the hybrid electrolyte with the [O]/[Li] ratio of 32. The electrochemical stability window of 4V ensures the hybrid electrolyte as a potential candidate for low voltage lithium ion batteries.

K-shell photoionization of Be-like boron (B+) ions: experiment and theory

Absolute cross sections for the K-shell photoionization of Be-like boron ions were measured with the ion–photon merged-beams technique at the Advanced Light Source synchrotron radiation facility. High-resolution spectroscopy with E/ΔE up to 8800 (ΔE ∼ 22 meV) covered the energy ranges 193.7–194.7 eV and 209–215 eV. Lifetimes of the strongest resonances are determined with relative uncertainties down to approximately 4% for the broadest resonance. The measured resonance strengths are consistent with 60% 1s22s2 1S ground-state and 40% 1s22s2p 3Po metastable-state ions in the primary ion beam and confirmed by comparison with independent absolute photo-recombination heavy-ion storage-ring measurements with B2 + ions using the principle of detailed balance. Experimental determination of the line width for the 1s2s22p 1Po resonance gives a value of 47 ± 2 meV and compares favourably to a theoretical estimate of 47 meV from the R-matrix with pseudo-states (RMPS) method. The measured line widths of the 1s2s2p2 3P, 3D resonances are 10.0 ± 2 meV and 32 ± 3 meV, respectively, compared to RMPS theoretical estimates of 9 meV and 34 meV.

GRAVITO-TURBULENT DISKS IN THREE DIMENSIONS: TURBULENT VELOCITIES VERSUS DEPTH

Characterizing turbulence in protoplanetary disks is crucial for understanding how they accrete and spawn planets. Recent measurements of spectral line broadening promise to diagnose turbulence, with different lines probing different depths. We use 3D local hydrodynamic simulations of cooling, self-gravitating disks to resolve how motions driven by "gravito-turbulence" vary with height. We find that gravito-turbulence is practically as vigorous at altitude as at depth: even though gas at altitude is much too rarefied to be itself self-gravitating, it is strongly forced by self-gravitating overdensities at the midplane. The long-range nature of gravity means that turbulent velocities are nearly uniform vertically, increasing by just a factor of 2 from midplane to surface, even as the density ranges over nearly three orders of magnitude. The insensitivity of gravito-turbulence to height contrasts with the behavior of disks afflicted by the magnetorotational instability (MRI); in the latter case, non-circular velocities increase by at least a factor of 15 from midplane to surface, with various non-ideal effects only magnifying this factor. The distinct vertical profiles of gravito-turbulence vs. MRI turbulence may be used in conjunction with measurements of non-thermal linewidths at various depths to identify the source of transport in protoplanetary disks.

High‐resolution spectroscopy of the lunar sodium exosphere

AbstractWe have applied high‐resolution Fabry‐Perot spectroscopy to the study of the lunar sodium exosphere for the study of exospheric effective temperature and velocity variations. Observing from the National Solar Observatory McMath‐Pierce Telescope, we used a dual‐etalon Fabry‐Perot spectrometer with a resolving power of 180,000 to measure line widths and Doppler shifts of the sodium D2 (5889.95 Å) emission line. Our field of view was 360 km, and measurements were made in equatorial and polar regions from 500 km to 3500 km off the limb. Data were obtained from full moon to 3 days following full moon (waning phase) in March 2009. Measured Doppler line widths within 1100 km of the sunlit east and south lunar limbs for observations between 5 and 40° lunar phase imply effective temperatures ranging between 3260 ± 190 and 1000 ± 135 K. Preliminary line center analysis indicates velocity displacements between different locations off the lunar limb ranging between 100 and 600 m/s from the lunar rest velocity with a precision of ±20 to ±50 m/s depending on brightness. Based on the success of these exploratory observations, an extensive program has been initiated that is expected to constrain lunar atmospheric and surface‐process modeling and help quantify source and escape mechanisms.

External cavity diode lasers with 5kHz linewidth and 200nm tuning range at 1.55μm and methods for linewidth measurement.

Two simple external cavity diode laser designs using fibre pigtailed gain chips are tested and their properties compared with a high end DBR fibre laser. These ECDLs demonstrate a FWHM linewidth as low as 5.2kHz with a fitted Lorentzian FWHM linewidth as low as 1.6kHz. Tuning ranges of 200nm covering 1420nm to 1620nm were demonstrated. To the best of our knowledge these are the narrowest linewidth and most broadly tunable external cavity diode lasers reported to date. The improvement in linewidth is attributed to greatly enhanced acoustic isolation allowed by using fiber coupled gain chips and by replacing kinematic mounts with a pair of rotatable wedges for cavity alignment which eliminates acoustic resonances. A detailed description and discussion of techniques used to characterize the frequency noise and linewidths of these lasers is provided.

Construction and Characterization of External Cavity Diode Lasers for Atomic Physics

Since their development in the late 1980s, cheap, reliable external cavity diode lasers (ECDLs) have replaced complex and expensive traditional dye and Titanium Sapphire lasers as the workhorse laser of atomic physics labs1,2. Their versatility and prolific use throughout atomic physics in applications such as absorption spectroscopy and laser cooling1,2 makes it imperative for incoming students to gain a firm practical understanding of these lasers. This publication builds upon the seminal work by Wieman3, updating components, and providing a video tutorial. The setup, frequency locking and performance characterization of an ECDL will be described. Discussion of component selection and proper mounting of both diodes and gratings, the factors affecting mode selection within the cavity, proper alignment for optimal external feedback, optics setup for coarse and fine frequency sensitive measurements, a brief overview of laser locking techniques, and laser linewidth measurements are included.

Construction and characterization of external cavity diode lasers for atomic physics.

Since their development in the late 1980s, cheap, reliable external cavity diode lasers (ECDLs) have replaced complex and expensive traditional dye and Titanium Sapphire lasers as the workhorse laser of atomic physics labs1,2. Their versatility and prolific use throughout atomic physics in applications such as absorption spectroscopy and laser cooling1,2 makes it imperative for incoming students to gain a firm practical understanding of these lasers. This publication builds upon the seminal work by Wieman3, updating components, and providing a video tutorial. The setup, frequency locking and performance characterization of an ECDL will be described. Discussion of component selection and proper mounting of both diodes and gratings, the factors affecting mode selection within the cavity, proper alignment for optimal external feedback, optics setup for coarse and fine frequency sensitive measurements, a brief overview of laser locking techniques, and laser linewidth measurements are included.

Temperaments of young stars: rapid mass accretion rate changes in T Tauri and Herbig Ae stars

Variability in emission lines is a characteristic feature in young stars and can be used as a tool to study the physics of the accretion process. Here we present a study of H{\alpha} variability in 15 T Tauri and Herbig Ae stars (K7-B2) over a wide range of time windows, from minutes, to hours, to days, and years. We assess the variability using linewidth measurements and the time series of line profiles. All objects show gradual, slow profile changes on time-scales of days. In addition, in three cases there is evidence for rapid variations in H{\alpha} with typical time-scales of 10 min, which occurs in 10% of the total covered observing time. The mean accretion-rate changes, inferred from the line fluxes,are 0.01-0.07 dex for time-scales of < 1 hour, 0.04-0.4 dex for time-scales of days, and 0.13-0.52 dex for time-scales of years. In Costigan et al. 2012 we derived an upper limit finding that the intermediate (days) variability dominated over longer (years) variability. Here our new results, based on much higher cadence observations, also provide a lower limit to accretion-rate variability on similar time-scales (days), thereby constraining the accretion rate variability physics in a much more definitive way. A plausible explanation for the gradual variations over days is an asymmetric accretion flow resulting in a rotational modulation of the accretion-related emission, although other interpretations are possible as well. In conjunction with our previous work, we find that the time-scales and the extent of the variability is similar for objects ranging in mass from ~ 0.1 to ~ 5 Msol. This confirms that a single mode of accretion is at work from T Tauri to Herbig Ae stars - across a wide range of stellar masses.

Micron and Nanometer Measuring Methods Based on Metrological Scanning Electron Microscope

Micron and nanometer dimensional metrology is an important part of integrated circuits manufacturing system and nanofabrication research work. Semiconductor device feature size has shrunk from the micron to dozen of nanometers. How to watch the micro structure clearly, identify its edge, and measure its dimension accurately are the major issues that need to be research. In this paper, a metrological scanning electron microscope (M-SEM) system with precision stage and laser interferometer is presented. Furthermore, this paper focuses on demonstrating a metrological SEM image edge detection algorithm which is the essential part of the metrological SEM system to realize the measurement of line width. The procedure of the algorithm is that SEM image is first analyzed by noise type according to the histogram characteristics. Then the image noise is reduced by specific filters. Furthermore, a specific interesting object image region is selected and pixel gray level values of the region are obtained by line scan. SEM image edges are determined by the characteristic of the pixel information in two possible cases. This algorithm preserves the edge details of the original image and detects the image edge automatically in an easy and fast way.

Measurement of the Intrinsic Parameters of Single-Mode VCSELs

A complete characterization of the working parameters of a long-wavelength vertical-cavity surface-emitting laser (VCSEL) is presented. A technique is described for extracting values for the parameters of semiconductor laser rate equations based on simple expressions for the laser power and linewidth as a function of the bias current. The differential carrier lifetime at threshold is estimated by using the linear relation between the laser linewidth and the bias current that is obtained for below threshold operation. High resolution CW optical spectrum measurements are performed to apply this technique for extraction of the parameters of a 1550-nm single-transverse mode VCSEL. Intensity noise spectrum analysis is used to complete our parameter extraction procedure and to compare with parameter values obtained from laser linewidth measurements.

Magnetization dynamics of cobalt grown on graphene

Ferromagnetic resonance (FMR) spin pumping is a rapidly growing field which has demonstrated promising results in a variety of material systems. This technique utilizes the resonant precession of magnetization in a ferromagnet to inject spin into an adjacent non-magnetic material. Spin pumping into graphene is attractive on account of its exceptional spin transport properties. This article reports on FMR characterization of cobalt grown on chemical vapor deposition graphene and examines the validity of linewidth broadening as an indicator of spin pumping. In comparison to cobalt samples without graphene, direct contact cobalt-on-graphene exhibits increased FMR linewidth—an often used signature of spin pumping. Similar results are obtained in Co/MgO/graphene structures, where a 1 nm MgO layer acts as a tunnel barrier. However, magnetometry, magnetic force microscopy, and Kerr microscopy measurements demonstrate increased magnetic disorder in cobalt grown on graphene, perhaps due to changes in the growth process and an increase in defects. This magnetic disorder may account for the observed linewidth enhancement due to effects such as two-magnon scattering or mosaicity. As such, it is not possible to conclude successful spin injection into graphene from FMR linewidth measurements alone.

High-spectral-resolution attosecond absorption spectroscopy of autoionization in xenon

The decay of highly excited states of xenon after absorption of extreme ultraviolet light is directly tracked via attosecond transient absorption spectroscopy using a time-delayed near-infrared perturbing pulse. The lifetimes of the autoionizing 5$s$5${p}^{6}$6$p$ and 5$s$5${p}^{6}$7$p$ channels are determined to be (21.9 \ifmmode\pm\else\textpm\fi{} 1.3) fs and (48.4 \ifmmode\pm\else\textpm\fi{} 5.0) fs, respectively. The observed values support lifetime estimates obtained by traditional linewidth measurements. The experiment additionally obtains the temporal evolution of the decay as a function of energy detuning from the resonance center, and a quantum mechanical formalism is introduced that correctly accounts for the observed energy dependence.

LOPUT Laser: A novel concept to realize single longitudinal mode laser

We propose a novel type of cavity design to generate single longitudinal mode laser known as LOPUT cavity. LOPUT cavity stands for linear orthogonally polarized modes resulting in unidirectional travelling wave cavity. The technique can be applied to both isotropic as well as anisotropic gain mediums. In the present paper, we applied the technique to anisotropic gain medium such as a-cut Nd:YVO4. Using the LOPUT cavity, we demonstrated nearly 2 W of single longitudinal mode laser with nearly diffraction-limited spatial profile. Linewidth measurement using a custom-made Fabry Perot interferometer revealed instrument-limited linewidth of ∼5 MHz at 1064 nm.

Strain relaxation and dislocation reduction in AlGaN step‐graded buffer for crack‐free GaN on Si (111)

AbstractGaN growth on Si (111) with reduced dislocation density and wafer bow requires the implementation of strain‐compensation techniques to counter the thermal expansion mismatch‐related tensile stresses. The ability to design the optimal buffer layer strategy for GaN growth on Si (111) relies on the knowledge of the relaxation processes that occur during the growth. In the AlGaN step‐graded buffer, the processes are complex, making it difficult to optimize the layer thicknesses, number of layers and compositions. Here, investigation of the relaxation processes as related to the microstructural evolution within the layers is performed. It is found that the use of x‐ray diffraction measurements of both line width broadening and relaxation reveal the characteristics of the dominant relaxation process of inclination of edge‐type dislocation. The methods and results presented here are expected to aid in the optimization for growth of improved quality and wafer bow‐free GaN on Si (111). (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

SALT long-slit spectroscopy of LBQS 2113-4538: variability of the Mg II and Fe II component

The Mg II line is of extreme importance in intermediate redshift quasars since it allows us to measure the black hole mass in these sources and to use these sources as probes of the distribution of dark energy in the Universe, as a complementary tool to SN Ia. Reliable use of Mg II requires a good understanding of all the systematic effects involved in the measurement of the line properties, including the contamination by Fe II UV emission. We performed three spectroscopic observations of a quasar LBQS 2113-4538 (z = 0.956) with the SALT telescope separated in time by several months and we analyze in detail the mean spectrum and the variability in the spectral shape. We show that even in our good-quality spectra the Mg II doublet is well fit by a single Lorentzian shape. We tested several models of the Fe II pseudo-continuum and showed that one of them well represents all the data. The amplitudes of both components vary in time, but the shapes do not change significantly. The measured line width of LBQS 2113-4538 identifies this object as a class A quasar. The upper limit of $3\%$ for the contribution of the Narrow Line Region (NLR) to Mg II may suggest that the separation of the Broad Line Region (BLR) and NLR disappears in this class of objects.

In-plane external fiber Fabry–Perot cavity comprising silicon micromachined concave mirror

Light trapping in optical cavities has many applications in optical telecommunications, biomedical optics, atomic studies, and chemical analysis. Efficient optical coupling in these cavities is an important engineering problem that affects greatly the cavity performance. Reported in-plane external fiber Fabry–Perot cavities in the literature are based on flat micromachined mirrors. In this case, the diffraction loss in the cavity is usually overcome by using an expensive-lensed fiber or by inserting a coated lens in the cavity leading to a long cavity with a small free spectral range. In this work, we report a Fabry–Perot cavity formed by a multilayer-coated cleaved-surface single-mode fiber inserted into a groove while facing a three-dimensional concave micromirror; both are fabricated by silicon micromachining. The light is trapped inside the cavity while propagating in-plane of the wafer substrate. Theoretical modeling is carried out, taking into account the effect of asymmetry in the mirror radii of curvature resulting from the micromachining process. A cavity is formed using a concave mirror with 200 and 100 μm in-plane and out-of-plane radii curvature, respectively. The presented cavity has a measured line width of 0.45 nm around 1330 nm showing a quality factor of about 3000, which resembles a one order of magnitude improvement over a flat-mirror cavity.

Comparative study of intersubband absorption in AlGaN/GaN and AlInN/GaN superlattices: Impact of material inhomogeneities

We report a systematic and quantitative study of near-infrared intersubband absorption in strained AlGaN/GaN and lattice-matched AlInN/GaN superlattices grown by plasma-assisted molecular-beam epitaxy as a function of Si-doping profile with and without \ensuremath{\delta} doping. For AlGaN/GaN, we obtained good theoretical agreement with experimental measurements of transition energy, integrated absorbance and linewidth by considering many-body effects, interface roughness, and calculations of the transition lifetime that include dephasing. For the AlInN/GaN system, experimental measurements of the integrated absorbance due to the superlattice transitions produced values more than one order of magnitude lower than AlGaN/GaN heterostructures at similar doping levels. Furthermore, observed transition energies were roughly 150 meV higher than expected. The weak absorption and high transition energies measured in these structures is attributed to columnar alloy inhomogeneity in the AlInN barriers observed in high-angle annular dark-field scanning transmission electron microscopy. We simulated the effect of these inhomogeneities using three-dimensional band-structure calculations. The inhomogeneities were modeled as AlInN nanorods with radially varying In composition embedded in the barrier material of the superlattice. We show that inclusion of the nanorods leads to the depletion of the quantum wells (QWs) due to localization of charge carriers in high-In-containing regions. The higher energy of the intersubband transitions was attributed to the relatively uniform regions of the QWs surrounded by high Al (95$%$) composition barriers. The calculated transition energy assuming Al${}_{0.95}$In${}_{0.05}$N barriers was in good agreement with experimental results.

Measurement of Acoustic Noise Induced Linewidth Broadening of Unpackaged Distributed Feedback Fiber Laser

The acoustic noise induced linewidth broadening phenomenon of distributed feedback fiber laser (DFB FL) is experimentally studied in this paper. Using the delayed self-homodyne method, we performed linewidth measurements on one unpackaged short cavity asymmetrical DFB FLs under increasing acoustic noise influence. The experiment results show the linewidth of tested laser increased from 5.8 KHz at 50 dB sound level to 32.5KHz at 80 dB sound level. This proves acoustic noise can drastically change the linewidth performance of unpackaged DFB FL. In addition, we performed another experiment on the same DFB FL to measure its linewidth with increasing tensile loads at fiber ends; the result shows a linewidth increase from 5.8 KHz at 0g tensile force to 51.2 KHz at 50g tensile force.

Single-shot soft x-ray laser linewidth measurement using a grating interferometer

The linewidth of a 14.7 nm wavelength Ni-like Pd soft x-ray laser was measured in a single shot using a soft x-ray diffraction grating interferometer. The instrument uses the time delay introduced by the gratings across the beam to measure the temporal coherence. The spectral linewidth of the 4d1S0-4p1P1 Ni-like Pd lasing line was measured to be Δλ/λ=3×10(-5) from the Fourier transform of the fringe visibility. This single shot linewidth measurement technique provides a rapid and accurate way to determine the temporal coherence of soft x-ray lasers that can contribute to the development of femtosecond plasma-based soft x-ray lasers.