Vertical Divergences Research Articles

5D tomographic phase-space reconstruction of particle bunches

We propose a new beam diagnostics method to reconstruct the phase space of charged particle bunches in five dimensions, which consist of the horizontal and vertical positions and divergences as well as the time axis. This is achieved by combining a quadrupole-based transverse phase-space tomography with the adjustable streaking angle of a polarizable X-band transverse deflection structure. We demonstrate with detailed simulations that the method is able to reconstruct various complex phase-space distributions and that the quality of the reconstruction depends on the number of input projections. This method allows for the identification and visualization of previously unnoticed detailed features in the phase-space distribution and can thereby be used as a tool toward improving the performance of particle accelerators or performing more accurate simulation studies. Published by the American Physical Society 2024

A Procedure for the Characterization and Comparison of 3-D LiDAR Systems

LiDARs are becoming one of the pillars for the environmental sensing required by advanced driver assistance system (ADAS). Driven by the automotive industry, many new manufacturers are continuously putting new LiDARs on the market, thus increasing their availability and, concomitantly, reducing prices. Accordingly, LiDARs are today finding many new applications also in other fields, such as agriculture and industrial automation. In this article, we describe and discuss a measurement procedure for the analysis and comparison of the performances of LiDARs and report an example of the results obtained from the characterization of one the most widespread LiDARs—the VLP 16 by Velodyne. The proposed measurement procedure and setup have been designed to allow quick and easy installation and analysis of most LiDARs. In particular, they have been designed to allow the straightforward investigation of performances such as the warm-up, stability, and errors in the measured coordinates and parameters such as the spots pattern, waist, and divergence of the laser beams, thus allowing to analyze probably the most relevant performances and parameters for scanning LiDARs. Errors in the measured coordinates have been estimated using an absolute interferometer, whereas the beam parameters have been analyzed using a camera system. As an example, the analysis of the performances of the VLP 16 revealed a warm-up time of about 42 min and errors of few millimeters over a measuring interval of about (2, 21) m. On the other hand, the analysis of the laser beams revealed the vertical and horizontal beam divergences of $\approx 1.2$ and $\approx 3.9$ mrad, respectively.

Single-Mode Lasers (1050 nm) of Mesa-Stripe Design Based on an AlGaAs/GaAs Heterostructure with an Ultra-Narrow Waveguide

The emission characteristics of single-mode lasers based on an AlGaAs/GaAs heterostructure with an ultra-narrow waveguide are studied. It is shown that using an ultra-narrow waveguide (100 nm) and thin (70 nm) wide-gap barriers at the waveguide/cladding interface makes narrower the vertical divergence of far-field emission. The lateral and vertical divergences are 5° and 18.5°, respectively, for the narrow-stripe (5.1 μm) single-mode lasers developed in the study. The lasers demonstrate efficient single-mode operation up to a power of 200 mW. Raising the current further gives rise to higher order modes, the maximum optical power in continuous-wave lasing being limited to 550 mW by overheating. Passing to the pulsed operation mode (pulse width 200 ns) makes it possible to raise the maximum peak optical power to 1500 mW.

Одномодовые лазеры (1050 нм) мезаполосковой конструкции на основе гетероструктуры AlGaAs/GaAs со сверхузким волноводом

The radiation properties of single-mode lasers based on an AlGaAs/GaAs heterostructure with an ultra-narrow waveguide are studied. It is shown that the use of an ultra-narrow waveguide (100 nm) and thin (70 nm) wide-gap barriers at the waveguide/cladding interface improves the vertical divergence. The lateral and vertical divergences were 5 and 18.5 degrees, respectively, for the developed narrow-stripe (5.1 µm) single-mode lasers. An efficient single-mode operation up to a power of 200 mW is demonstrated. A further increase in current leads to the onset of higher-order modes, while the maximum optical power achieved under continuous-wave (CW) operation is limited by overheating and is 550 mW. The transfer to a pulsed operation (pulse width 200 ns) made it possible to raise the maximum peak optical power to 1500 mW.

Double‐Diffusive Layering in the Canada Basin: An Explanation of Along‐Layer Temperature and Salinity Gradients

AbstractDouble‐diffusive mixing gives rise to layered structures in the Arctic Ocean: layers within a double‐diffusive staircase overlying deeper layers associated with thermohaline intrusions. These layers exhibit well‐defined lateral temperature and salinity gradients. Gradients in salinity along individual layers change sign with depth, while along‐layer gradients in temperature remain the same sign with depth. A theoretical formalism is put forward to explain these features in terms of vertical divergences of double‐diffusive fluxes; temperature and salinity gradients along layers are set by the depth‐dependent ratio of double‐diffusive heat to salt fluxes. Examination of fine structure in temperature and salinity profiles reveals how the net flux ratio depends upon whether the layer is part of an evolving thermohaline intrusion or a staircase. The physical framework in context with observations of varying along‐layer gradients in temperature and salinity provides evidence for thermohaline intrusions evolving to a staircase and describes the parameters that dictate this process. Results bring new understanding to heat and salt transport in the Arctic Ocean as well as the physics of double‐diffusive layering in the world's oceans.

High-power high-brightness 980 nm lasers with >50% wall-plug efficiency based on asymmetric super large optical cavity.

High-power high-brightness super large optical cavity laser diodes with an optimized epitaxial structure are investigated at the wavelength of 980 nm range. The thicknesses of P- and N-waveguides are prudently chosen based on a systematic consideration about mode characteristics and vertical far-field divergences. Broad area laser diodes show a high internal quantum efficiency of 98% and a low internal optical loss of 0.58 cm-1. The ridge-waveguide laser with 7 μm ridge and 3 mm cavity yields 1.9 W single spatial mode output with far-field divergence angles of 6.8° in lateral and 11.5° in vertical at full width at half maximum under 2 A CW operating current. The corresponding M2 values are 1.77 and 1.47 for lateral and vertical, respectively, and the corresponding brightness is 76.8 MW‧cm-2‧sr-1. The far-field divergence angles with 95% power content are in the range of 24.7° to 26.1° across the whole measured range.

Neutron-beam former for the REVERANS reflectometer with a vertical scattering plane

A device that forms a vertically diverging neutron beam is described. The device allows scanning at the angle of incidence of neutrons on a fluid surface in a reflectometer with a vertical scattering plane. Computer simulation of the former is carried out, and the beam characteristics (horizontal and vertical divergences and the neutron energy spectrum) are obtained. These characteristics are compared with experimental data. Three units are the main advantages of the former: specially fabricated input and output collimators and neutron filters. The reasons for differences in the experimental and simulated data are discussed.

Some features in the angular divergence of relativistic electron beams reflected and refracted by foil

The horizontal and vertical angular divergences of relativistic electron beams passing through a foil and reflected by a foil are experimentally measured. The effect of the angle between the electron beam and the foil plane on the intensity and angular divergence of beams is studied. The interaction of particles with a copper foil 50 μm thick and aluminum foil 200 μm thick is studied. A microtron with a particle energy of 7.4 MeV is used as an electron source.

On the salt balance of Tampa Bay

A three-dimensional, numerical circulation model, with resolution as high as 20m at important mass conveyances (inlets, channels, bridge causeways, and rivers), is used to diagnose the point by point salt balances for Tampa Bay, FL. While the details of the salt flux divergences and the salt fluxes vary throughout the bay, each is fully three dimensional. On experimental duration (three month) average, the total (horizontal plus vertical) advective salt flux divergence is mainly balanced by the vertical diffusive salt flux divergence, except near the bottom of the deep shipping channel, where horizontal diffusive salt flux divergence is also important. Instantaneously, the local rate of change of salinity is primarily controlled by the advective salt flux divergence, with a secondary contribution by the vertical diffusive salt flux divergence everywhere and the horizontal diffusive salt flux divergence near the channel bottom. To examine the role of tidal pumping, the advective salt fluxes and divergences are further decomposed into the products of the mean salinity and velocity, and the correlation between the salinity and velocity fluctuations. The horizontal and vertical advective salt flux divergences by the mean quantities are equally large and counterbalancing (by continuity), with their sum being a small, but significant residual. The horizontal and vertical advective salt flux divergences due to tidal pumping are relatively small (when compared with the mean quantities) and counterbalancing; but, when summed their residual is comparable in magnitude to that by the mean quantities. So whereas the salt fluxes by tidal pumping are of secondary importance to the salt fluxes by the mean quantities, their total flux divergences are of comparable importance. The salt flux components in all three dimensions (axial, transverse and vertical) themselves vary along the Tampa Bay axis, and these findings may be typical of coastal plain estuaries given their geometrical complexities. Being that the distribution of salt flux bears upon the flux distributions of other scalars (e.g., nutrients, fish larvae, etc.) our findings for salt flux also have broader ecological implications.

Applications of a Moist Nonhydrostatic Formulation of the Spectral Energy Budget to Baroclinic Waves. Part I: The Lower-Stratospheric Energy Spectra

Abstract The authors investigate the mesoscale dynamics that produce the lower-stratospheric energy spectra in idealized moist baroclinic waves, using the moist nonhydrostatic formulation of spectral energy budget of kinetic energy and available potential energy by J. Peng et al. The inclusion of moist processes energizes the lower-stratospheric mesoscale, helping to close the gap between observed and simulated energy spectra. In dry baroclinic waves, the lower-stratospheric mesoscale is mainly forced by weak downscale cascades of both horizontal kinetic energy (HKE) and available potential energy (APE) and by a weak conversion of APE to HKE. At wavelengths less than 1000 km, the pressure vertical flux divergence also has a significant positive contribution to the HKE; however, this positive contribution is largely counteracted by the negative HKE vertical flux divergence. In moist baroclinic waves, the lower-stratospheric mesoscale HKE is mainly generated by the pressure and HKE vertical flux divergences. This additional HKE is partly converted to APE and partly removed by diffusion. Another negative contribution to the mesoscale HKE is from the forcing of a visible upscale HKE cascade. Besides the conversion of HKE, however, the three-dimensional divergence also has a significant positive contribution to the mesoscale APE. With these two direct APE sources, the lower-stratospheric mesoscale also undergoes a much stronger upscale APE cascade. These results suggest that both downscale and upscale cascades through the mesoscale are permitted in the real atmosphere and the direct forcing of the mesoscale is available to feed the upscale energy cascade.

Noninvasive emittance and energy spread monitor using optical synchrotron radiation

We propose a design for a minimally perturbing diagnostic minichicane, which utilizes optical synchrotron radiation (OSR) generated from magnetic bends in the chicane, to measure the rms horizontal and vertical beam sizes, divergences, emittances, Twiss parameters and energy spread of a relativistic electron beam. The beam is externally focused to a waist at the first bend and the OSR generated there can be used to measure the rms beam size. Subsequent pairs of bends produce far field OSR interferences (OSRI) whose visibility depends on the beam energy spread and the angular divergence. Under proper conditions, one of these two effects will dominate the OSRI visibility from a particular pair of bends and can be used to diagnose the dominant effect. The properties of different configuration of bends in the chicane have been analyzed to provide an optimum diagnostic design for a given set of beam parameters to: (1) provide a sufficient number of OSR interferences to allow a measurement of the fringe visibility; (2) minimize the effect of coherent synchrotron radiation and space charge forces on the particles motion; and (3) minimize the effect of compression on the bunch length as the beam passes through the chicane. A design for the chicane has been produced for application to the FERMI free electron laser facility and by extension to similar high brightness linear accelerators. Such a diagnostic promises to greatly improve control of the electron beam optics with a noninvasive measurement of beam parameters and allow on-line optics matching and feedback.

The IMAGINE instrument: first neutron protein structure and new capabilities for neutron macromolecular crystallography

The first high-resolution neutron protein structure of perdeuterated rubredoxin from Pyrococcus furiosus (PfRd) determined using the new IMAGINE macromolecular neutron crystallography instrument at the Oak Ridge National Laboratory is reported. Neutron diffraction data extending to 1.65 Å resolution were collected from a relatively small 0.7 mm(3) PfRd crystal using 2.5 d (60 h) of beam time. The refined structure contains 371 out of 391, or 95%, of the D atoms of the protein and 58 solvent molecules. The IMAGINE instrument is designed to provide neutron data at or near atomic resolution (1.5 Å) from crystals with volume <1.0 mm(3) and with unit-cell edges <100 Å. Beamline features include novel elliptical focusing mirrors that deliver neutrons into a 2.0 × 3.2 mm focal spot at the sample position with full-width vertical and horizontal divergences of 0.5 and 0.6°, respectively. Variable short- and long-wavelength cutoff optics provide automated exchange between multiple-wavelength configurations (λmin = 2.0, 2.8, 3.3 Å to λmax = 3.0, 4.0, 4.5, ∼20 Å). These optics produce a more than 20-fold increase in the flux density at the sample and should help to enable more routine collection of high-resolution data from submillimetre-cubed crystals. Notably, the crystal used to collect these PfRd data was 5-10 times smaller than those previously reported.

Reflections on the surface energy imbalance problem

The ‘energy imbalance problem’ in micrometeorology arises because at most flux measurement sites the sum of eddy fluxes of sensible and latent heat (H+λE) is less than the available energy (A). Either eddy fluxes are underestimated or A is overestimated. Reasons for the imbalance are: (1) a failure to satisfy the fundamental assumption of one-dimensional transport that is necessary for measurements on a single tower to represent spatially-averaged fluxes to/from the underlying surface, and (2) measurement errors in eddy fluxes, net radiation and changes in energy storage in soils, air and biomass below the measurement height. Radiometer errors are unlikely to overestimate A significantly, but phase lags caused by incorrect estimates of the energy storage terms can explain why H+λE systematically underestimates A at half-hourly time scales. Energy closure is observed at only 8% of flux sites in the La Thuile dataset (http://www.fluxdata.org/DataInfo/default.aspx) with half-hourly averages but this increases to 45% of sites using 24h averages because energy entering the soil, air and biomass in the morning is returned in the afternoon and evening. Unrealistically large and positive horizontal gradients in temperature and humidity are needed for advective flux divergences to explain the energy imbalance at half-hourly time scales. Imbalances between H+λE and A still occur in daily averages but the small residual energy imbalances are explicable by horizontal and vertical advective flux divergences. Systematic underestimates of the vertical heat flux also occur if horizontal u′T′ covariances contaminate the vertical w′T′ signal due to incorrect coordinate rotations. Closure of the energy balance is possible at half-hourly time scales by careful attention to all sources of measurement and data processing errors in the eddy covariance system and by accurate measurement of net radiation and every energy storage term needed to calculate available energy.

Reoperação nas esotropias congênita e essencial adquirida não acomodativa

To analyze the results in patients reoperated from congenital and essential esotropia. A retrospective chart review of 393 patients who underwent surgery from 2000-2004 was performed. Subjects were divided into two groups: Congenital esotropia (91 patients) and essential esotropia (302 cases). Among congenital cases we had 9 reoperations (9.9%). There were undercorrections (3.3%), overcorrections (2.2%), anisotropia (V) (1.1%), hypotropia (1.1%) and dissociatd vertical divergences (2.2%). Among the essential cases, there were 31 (10.3%) reoperations due to undercorrections (n=6.6%), overcorrections (n=2%) and hypotropias (1.7%). Outcomes reoperations rates were 9.9% and 10.2% between congenital and essential esotropias with a higher rate of undercorrections. Amblyopia in both groups and deviations higher than 50∆ in essential esotropias seems to be the most important factors for poor results.

Field estimates of scalar advection across a canopy edge

Measurements of the horizontal and vertical fluxes of energy and mass were taken at a crop canopy edge and downwind of it to examine the effects of inhomogeneity on surface–atmosphere exchange, for the ideal case of flat uniform terrain. Energy balance closure was also examined and the effects of the often-neglected advection terms on the energy budget were evaluated. The results show that neither vertical nor horizontal advection should be neglected for moderate distances downwind from heterogeneous boundaries, with the energy budget closure near the leading edge improved by more than 20% with the inclusion of the horizontal and vertical advection of latent and sensible heat. Significant mean advective horizontal and vertical flux divergences of water vapor and temperature were found even in typical daytime conditions. In stable conditions horizontal advection can be responsible for more than 15% of the scalar (water vapor) transport 136 canopy heights downwind of a change in water vapor source density and surface roughness.

Latent heat flux measurements over complex terrain by airborne water vapour and wind lidars

AbstractVertical profiles of the latent heat flux in a convective boundary layer (CBL) are obtained for the first time over complex terrain with airborne water vapour differential absorption lidar and Doppler wind lidar. During the Convective and Orographically‐induced Precipitation Study (COPS) over the Black Forest mountains in south‐western Germany both lidars were installed nadir‐viewing onboard the Falcon research aircraft of the Deutsches Zentrum für Luft‐ und Raumfahrt (DLR). On 30 July 2007, additional in situ measurements by the Karlsruhe Institute of Technology (KIT) were performed with a Dornier‐128 aircraft that flew below the Falcon. This unique instrument configuration allows us to validate the lidar‐derived fluxes and to assess lidar‐specific issues such as instrument noise and data gaps that impinge on the results. The cospectra of in situ humidity and vertical velocity peak at wavelengths between 1 and 3 km and reveal that the dominant scales of turbulent transport are larger than 700 m in dimension. Consequently the airborne lidars' horizontal and vertical resolution of ∼ 200 m is sufficient to capture most of the flux. The lidar and in situ fluxes of five collocated 45 km flight legs agree within ±20%; the average difference over the total distance of 225 km is 3%. A flux comparison with ground‐based water vapour Raman and wind lidars shows agreement within the instruments' accuracies under low‐wind conditions. All latent heat fluxes vary between 100 and 500 W/m2 in the CBL and have small vertical divergences. Vertical velocity spectra in the mid‐CBL enable us to estimate the dissipation rate of turbulent kinetic energy that amounts to 5 × 10−4 m2 s−3 in the Rhine Valley and 10−3 m2 s−3 over the Black Forest mountains. This new airborne lidar instrumentation proves to be a valuable tool for the study of CBL processes and variability, particularly over complex terrain. Copyright © 2011 Royal Meteorological Society

Temperature sensitivity (T) of tensile-strained GaAsP/(AlGa)As double-barrier separate confinement heterostructure laser diodes for 800 nm band

The temperature sensitivity of the double-barrier separate confinement heterostructure (DBSCH) laser diodes (LDs), intended for high-power, low vertical beam divergence emission, was shown to be somewhat lower than that of the large optical cavity (LOC) devices of similar beam divergences. For the lowest beam divergences, it still remains considerably high, resulting in low characteristic temperatures T0 not exceeding 80 K in the LDs of the vertical beam divergences below 15°. In this work, the decrease in the T0 values of such tensile-strained GaAsP/(AlGa)As DBSCH LDs has been found primarily due to an increased, thermally activated occupation of the heavy-hole subband and, to a minor degree, occupation of the second quantum level, both giving rise to transitions that do not contribute to the optical gain. This is caused by the higher and more temperature-dependent at-threshold band filling for devices of reduced confinement factor (Γ) aimed at achieving low beam divergence. This phenomenon seems to be common for all the tensile-strained LDs and acts in addition to other mechanisms that decrease the T0, such as the carrier escape from a quantum well to surrounding layers. However, in DBSCH LDs no carrier escape has been detected, presumably because of their thin waveguide layers. This can explain the somewhat higher T0 values of these devices when compared to their LOC counterparts.

Surface boundary-layer variability off Northern California, USA, during upwelling

Abstract A five-element mooring array is used to study surface boundary-layer transport over the Northern California shelf from May to August 2001. In this region, upwelling favorable winds increase in strength offshore, leading to a strong positive wind stress curl. We examine the cross-shelf variation in surface Ekman transport calculated from the wind stress and the actual surface boundary-layer transport estimated from oceanic observations. The two quantities are highly correlated with a regression slope near one. Both the Ekman transport and surface boundary layer transport imply curl-driven upwelling rates of about 3×10 −4 m s −1 between the 40 and 90 m isobaths (1.5 and 11.0 km from the coast, respectively) and curl-driven upwelling rates about 1.5×10 −4 m s −1 between the 90 and 130 m isobaths (11.0 and 28.4 km from the coast, respectively). Thus curl-driven upwelling extends to at least 25 km from the coast. In contrast, upwelling driven by the adjustment to the coastal boundary condition occurs primarily inshore of the 40-m isobath. The upwelling rates implied by the differentiating the 40-m transport observations with the coastal boundary condition are up to 8×10 −4 m s −1 . The estimated upwelling rates and the temperature–nitrate relationship imply curl-driven vertical nitrate flux divergences are about half of those driven by coastal boundary upwelling.

The New Materials Science Diffractometer STRESS-SPEC at FRM-II

In response to the development of new materials and the application of materials and components in new technologies the direct measurement, calculation and evaluation of textures and residual stresses has gained worldwide significance in recent years. Non-destructive analysis for phase specific residual stresses and textures is only possible by means of diffraction methods. In order to cater for the development of these analytical techniques the new Materials Science Diffractometer STRESS-SPEC at FRM-II is designed to be equally applied to texture and residual stress analyses by virtue of its flexible configuration. The system compromises a highly flexible monochromator setup using three different monochromators: Ge (511), bent silicon (400) and pyrolitic graphite (PG). This range of monochromators and the possibility to vary the take-off angles from 2θM = 35º to 110º allows wavelength adjustment such that measurements can be performed around a scattering angle of 2θS ~ 90º. This is important in order to optimise neutron flux and resolution, especially for stress analysis on components, since the gauge volume element in that case is cubic and large vertical divergences due to focusing monochromators do not affect the spatial resolution. The instrument is now available for routine operation and here we will present details of recent experiments and instrument performance.

High-Power Low Vertical Beam Divergence 800-nm-Band Double-Barrier-SCH GaAsP&amp;#8211;(AlGa)As Laser Diodes

High-power double-barrier separate confinement heterostructure (SCH) GaAsP-AlGaAs-GaAs laser diodes designed for low vertical beam divergence emission at 800-nm band are presented. Insertion of thin wide-gap (low refractive index) barrier layers at the interfaces between the waveguide and cladding layers of an initial SCH causes an optical confinement weakening. As a result, the vertical divergences down to 16deg and 13deg have been obtained, depending on the design version. Similar threshold current densities, higher characteristic temperatures T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> compared to the high-power large optical cavity (LOC) lasers of comparable beam divergences and promising high-power performance make this design an alternative to LOC solution