Large Divergence Angle Research Articles

Supersonic two-phase flow of CO 2 through converging–diverging nozzles for the ejector refrigeration cycle

CO 2 is environmentally friendly, safe and more suitable to ejector refrigeration cycle than to vapor compression cycle. Supersonic two-phase flow of CO 2 in the diverging sections of rectangular converging–diverging nozzles was investigated. The divergence angles with significant variation of decompression were 0.076°, 0.153°, 0.306° and 0.612°. This paper presents experimental decompression phenomena which can be used in designing nozzles and an assessment of Isentropic Homogeneous Equilibrium (IHE). Inlet conditions around 6–9 MPa, 20–37 °C were used to resemble ejector nozzles of coolers and heat pumps. For inlet temperature around 37 °C, throat decompression boiling from the saturated liquid line, supersonic decompression and IHE solution were obtained for the two large divergence angles. For divergence angles larger than 0.306°, decompression curves for inlet temperature above 35 °C approached IHE curves. For divergence angles smaller than 0.306° or for nozzles with inlet temperature below 35 °C, IHE had no solution.

First demonstration of collimation and monochromatisation of a laser accelerated proton burst

AbstractLaser produced ion beams have a large divergence angle and a wide energy spread. To our knowledge, this is the first demonstration of collimation and monochromatisation of laser accelerated proton beams, using a permanent quadrupole magnet lens system. It acts as a tunable band pass filter by collimating or focusing the protons with the same energy. Because it gathers nearly the whole proton emission, a strong enhancement of the beam density appears. For the collimated beam, an increase of the proton density in the (3.7 ± 0.3) MeV energy band up to a factor of ~30, from possible 40, relative to the non-collimated beam is demonstrated. With the help of this simple, reliable, and well established technique new perspectives will be opened for science and technology, monoenergetic ion beams can be attained in any lab, where a source of laser accelerated ions exist. This finding enables to apply afterward well known beam steering techniques to the formed ion beam, which are applied in conventional accelerators to manipulate the beam parameters or to transport the beams and make them use in many application.

Fabrication of Mesa Shaped InGaN-Based Light-Emitting Diodes Through a Photoelectrochemical Process

InGaN-based light-emitting diodes (LEDs) were fabricated to have a higher light extraction through the photoelectrochemical (PEC) mesa shaping process. After the PEC selective wet oxidation and wet etching processes, stable and controllable crystallographic etching planes were formed as p-type GaN { $$ 10\overline{11} $$ } planes and n-type GaN { $$ 10\overline{1} 0 $$ } planes included at an angle of 27 deg. The ever-present cone-shaped structure of a PEC-treated LED has a larger light scattering area and higher light extraction cones on the mesa sidewall, as analyzed by microphotoluminescence and light output power measurement. This cone-shaped-sidewall LED has a higher light output power and a larger divergence angle compared with a conventional LED measured in an LED chip form.

Simulation of secondary electron emission in an electron gun

To decrease the size of electron beam in an electron gun, sometimes an aperture with a small hole is used to cut off the electrons with large divergence angle. However, a few secondary electrons may be emitted when the primary electrons bombard on this aperture. This article simulates the secondary electron emission in an electron gun. In the simulation, the aperture is suggested to be a perfect metal electrode first. Therefore, there is no secondary electron emission when the primary electrons bombard on it. Then, it is assumed that some secondary electrons and back scatters can emit from the aperture. This paper also changes the diameter of the hole in aperture. From the comparison of the spot on the screen, the influence of the secondary electrons on the spot profile can be estimated. © 2008 Elsevier B.V. All rights reserved.

Wavefront measurements of diode laser beams with large dynamic ranges

We propose and demonstrate a method for the measurement of the wavefronts of high-power diode laser beams with large dynamic ranges. Our wavefront sensor consists of a movable pinhole and a wavefront-slope detector. The measurement results show that the wavefront sensor exhibits a large dynamic range of pi/2 to -pi/2 and a high precision on the measured average wavefront slope. The wavefronts of high-power diode laser beams having large divergence angles at arbitrary locations (including near and far fields) can be reconstructed via the wavefront measurement at a given location. The amplitude and phase distributions of a laser beam could be determined from the measured optical field data using diffraction theory. The experimental measurement of the wavefront of a 980 nm diode laser beam will be presented and discussed.

Approach for simultaneous measurement of two-dimensional angular distribution of charged particles. III. Fine focusing of wide-angle beams in multiple lens systems

This paper provides a way of focusing wide-angle charged-particle beams in multiple lens systems. In previous papers [H. Matsuda, Phys. Rev. E 71, 066503 (2005); 74, 036501 (2006)], it was shown that an ellipsoidal mesh, combined with electrostatic lenses, enables correction of spherical aberration over wide acceptance angles up to +/-60 degrees . In this paper, practical situations where ordinary electron lenses are arranged behind the wide-angle electrostatic lenses are taken into account using ray tracing calculation. For practical realization of the wide-angle lens systems, the acceptance angle is set to +/-50 degrees . We note that the output beams of the wide-angle electrostatic lenses have somewhat large divergence angles which cause unacceptable or non-negligible spherical aberration in additional lenses. A solution to this problem is presented showing that lens combinations to cancel spherical aberration are available, whereby wide-angle charged-particle beams can be finely focused with considerably reduced divergence angles less than +/-5 degrees .

Measurements of Energy Transport Patterns in Solid Density Laser Plasma Interactions at Intensities of5×1020 W cm−2

Kalpha x-ray emission, extreme ultraviolet emission, and plasma imaging techniques have been used to diagnose energy transport patterns in copper foils ranging in thickness from 5 to 75 microm for intensities up to 5x10(20) W cm-2. The Kalpha emission and shadowgrams both indicate a larger divergence angle than that reported in the literature at lower intensities [R. Stephens, Phys. Rev. E 69, 066414 (2004)]. Foils 5 microm thick show triple-humped plasma expansion patterns at the back and front surfaces. Hybrid code modeling shows that this can be attributed to an increase in the mean energy of the fast electrons emitted at large radii, which only have sufficient energy to form a plasma in such thin targets.

Effects of shock waves on spatial distribution of proton beams in ultrashort laser-foil interactions

The characteristics of proton beam generated in the interaction of an ultrashort laser pulse with a large prepulse with solid foils are experimentally investigated. It is found that the proton beam emitted from the rear surface is not well collimated, and a “ring-like” structure with some “burst-like” angular modulation is presented in the spatial distribution. The divergence of the proton beam reduces significantly when the laser intensity is decreased. The “burst-like” modulation gradually fades out for the thicker target. It is believed that the large divergence angle and the modulated ring structure are caused by the shock wave induced by the large laser prepulse. A one-dimensional hydrodynamic code, MED103, is used to simulate the behavior of the shock wave produced by the prepulse. The simulation indicates that the rear surface of the foil target is significantly modified by the shock wave, consequently resulting in the experimental observations.

Moiré fringes of cold neutron with large divergence angle

Moiré fringes were observed as a bright and high-contrast image using a neutron spin interferometer with a relatively divergent cold neutron beam at the MINE2 beam line of JRR-3M. The two spin states were selectively deflected with the relative angle in the range of 92–184 nrad on transmission through the magnetic field gradient in the range of 3.2–6.4 G/cm produced by a 5 cm long quadrupole electromagnet. We analyzed the result with a first-order calculation taking into account the finite beam divergence and found that the beam divergence is required to be less than the angular separation of individual Moiré loci, for the observation of Moiré fringes, and is not required to be less than the angular separation of the two beam paths.

Homologues of the Easily Ionized Compound Mo2(hpp)4 Containing Smaller Bicyclic Guanidinates

Two bicyclic guanidinate ligands consisting of 5,5-membered (tbo) and 5,6-membered (tbn) rings have been used for the preparation of dimolybdenum compounds, such as Mo2(tbo)4 and Mo2(tbo)4Cl, and species containing Mo2(tbn)4(n+) with n = 0-2. The compounds with quadruply bonded Mo2(4+) species are strong reducing agents and have potentials of about -1 V (vs Ag/AgCl) for the Mo2(5+/4+) process. The structure of the THF solvate of Mo2(tbo)4 shows the longest Mo-Mo bond distance, 2.1453(4) A, for a quadruply bonded species, and this is due to a large divergent angle induced by the geometry of the ligand. This distance increases to 2.2305(8) A upon oxidation by CH2Cl2 to Mo2(tbo)4Cl. For the 5,6-membered-ring ligand tbn, even though the divergent angle is large compared to formamidinate ligands, it is not as large as that in tbo, and the Mo-Mo distance in Mo2(tbn)4, 2.082(1) A, is in the normal range for paddlewheel Mo2(4+) compounds. This distance increases to 2.2233(8) A upon oxidation by O2 in CH2Cl2, which forms Mo2(tbn)4Cl2 x CH2Cl2.

Large optical cavity and small vertical divergence angle semiconductor lasers

A novel coupled large optical cavity cascaded by tunnel-junction semiconductor lasers is put forward to resolve the major difficulties of ordinary laser diodes. In this structure several active regions are cascaded by tunnel junctions to couple a large optical cavity. This structure can solve the problem of catastrophic optical damage of facet and large vertical divergence caused by thin emitting area in ordinary laser diodes. The near-field facalur size reaches 1μm. Low-pressure metal-organic chemical vapor deposition is adopted to grow the novel semiconductor lasers. Slope efficiency as high as 0.80W/A per facet and vertical divergence angle of 20°and threshold current density of 277 A/cm2 are achieved from an uncoated novel laser device.

Compact high-resolution retarding field energy analyzer for space-charge-dominated electron beams

We have developed a compact high-resolution retarding field energy analyzer for measuring the energy spread of space-charge-dominated electron beams. This energy analyzer has a cylindrical electrode to overcome the defocusing effects due to space-charge forces, beam trajectories, aperture effect, etc. The device provides excellent spatial and temporal information on the beam energy spread. Single-particle simulation shows that this energy analyzer has very good resolution for low-energy electron beams of several kilovolts and with large divergence angles. The energy analyzer has been tested with 2.5 keV, 60 mA electron beams. The measured energy spread is also compared with the theoretical calculations taking into account two main energy spread sources, namely, the Boersch effect and the longitudinal-longitudinal relaxation.

Enhancement of Numerical Aperture of Liquid Crystal Microlenses Using a Stacked Electrode Structure

A liquid crystal (LC) microlens with a stacked electrode structure is fabricated by attaching a transparent flat electrode outside a conventional LC microlens. Numerical aperture (NA) properties in two driving methods (an addition type and a subtraction type) are discussed. NA of LC microlens in the addition-type driving method is almost the same as that of the conventional LC microlens, while in the subtraction type, NA is much larger. The enhancement of NA is explained by considering the spatial distribution of the electric field in the LC layer. The dependence on thickness of the insulating layer (ti) of the maximum NA (NAmax) when the applied voltage is varied is also discussed. In the subtraction type, NAmax strongly depends on ti and takes a maximum value when ti is varied. The enhancement of NA leads to the application of LC microlens as a collimating lens of a light source with a large divergence angle such as a laser diode.

Collimating of diverging laser diode beam using graded-index optical fiber

This paper presents a technique for collimating a diverging beam from a laser diode using graded-index optical fiber. The optical set-up is relatively simple and easy to operate. The results show that laser beam of large divergent angle in the range of 10–35° can be reduced to a fully collimated beam with a divergent angle of less than 0.05°. The theory of the method as well as some experimental results is presented.

Monochromatic all-sky scanner: a quantitative imager of faint atmospheric emissions

Many ground-based studies of the dynamics of the lower thermosphere and ionosphere have been performed using meridian scanning photometers and all-sky cameras. The two instruments strike different balances between quality and quantity or sensitivity versus large field of view. A large divergence angle in a wide-angle system requires large bandwidth filters that limit detectability of faint atmospheric emissions that are due to low signal-to-background ratio. All-sky imaging to as low as 80-deg zenith angle is important in addressing issues such as horizontal wavelength of individual waves and size of wave packets in the neutral atmosphere, and size and dynamics of red arcs and F-layer patches. A new instrument for remote sensing of the Earth's upper atmosphere and its near-space environment from the ground is described. It affords true all-sky imaging at near-monochromatic wavelengths for faint airglow and auroral emissions by combining a two-mirror scanner with a zenith-looking photometer.

ERROR ANALYSIS FOR THE FAR-FIELD OF A SMALL PLANE SOURCE

Based on a rigorous far-field solution of the Helmholtz equation,the dependence of the far-field of the light wave with a large divergence angle on the perturbation of the source profile is discussed,and the error formulas of the far-field amplitude and phase are also given.It is shown that the far-field errors must be described by using the “error area” of the source.In the paraxial region,the far-field amplitude and phase are not sensitive to the source perturbation,but,in off-axis region,they may be sensitive.

Optical characterization and coagulation performance of side-emitting fiber delivery systems for laser therapy of benign prostatic hyperplasia: A comparative study

Objectives Currently, various side-emitting optical fibers with different tip geometry are used transurethrally to deliver laser radiation for treatment of benign prostatic hyperplasia (BPH). Since fiber tip design could profoundly affect the size and profile of the emitted laser beam, and consequently the tissue response and the extent of tissue coagulation, we evaluated commercially available fibers in regard to their optical characteristics and their ability to coagulate tissue in a controlled experimental setting. Methods Thirteen fibers manufactured by different companies and clinically used at the present time were tested using a surgical neodymium:yttrium-aluminum-garnet laser. The profile of the laser beam delivered via each fiber was imaged on a CCD camera at various distances and evaluated by means of a laser beam analyzer. Beam divergence angle was then calculated for each tip. Tissue coagulation effects were assessed by irradiating samples of beef muscle immersed in water at 37 °C. The fiber tip was kept 2.5 mm away from the tissue and irrigation was maintained at flow rate of 350 to 400 cc/min during irradiation. Laser powers of 20, 40, and 60 W were used for 180, 90, and 60 seconds, respectively, delivering a total energy of 3600 J. Results The results of the optical evaluation divided the fibers into two major groups: broad beam with large divergence angle and narrow beam with small divergence angle. Statistical analysis of the data (using analysis of variance) showed that volumes of coagulated tissue were significantly larger for broad beam fibers than for narrow beam fibers (1.15 ± 0.32 versus 0.89 ± 0.34 cm 3; P <0.05). Also, significantly larger volumes were obtained for 20 W when compared with 60 W (1.08 ± 0.43 versus 0.88 ± 0.27 cm 3; P <0.05). Conclusions The laser power density delivered by individual fibers to the prostate tissue may vary significantly, thus greatly affecting the extent of tissue coagulation. Therefore, irradiation parameters must be optimized for each fiber type.

On the image contrast from dislocations in high-angle annular dark-field scanning transmission electron microscopy

Abstract High-angle annular dark-field scanning-transmission electron microscopic imaging of inclined dislocation segments revealed a number of characteristic contrast effects that have been shown to depend on the specific position of the dislocation in the foil. The dislocation contrast is initially very dark at the entrant foil surface due to stress relaxation-induced scattering of the incident electrons. Below the entrant surface of the foil, the dislocation exhibits oscillatory contrast which disappears for large incident beam divergence angles. Ultimately, the dislocation contrast remains bright beyond a certain depth in the crystal towards the exit foil surface. A qualitative Bloch-wave scattering description has been formulated to describe consistently the observed contrast features.

203 広がり角の大きい正角錐ディフューザ内流れの可視化

In the duct having a large divergence angle of square cross section, a slight difference of state of flow occured in the neighborhood of throat wall surface at the upstream inlet and in its four corners grows rapidly at the inlet of divergence duct and makes the entire flow in the duct not uniform unsteady flow. Also in the case of a rapid velocity of flow, a separation from the wall surface occurs, however, the state of separation is different in the corners and the center of wall surface. A reversed stream occurs in the place where the separation takes place. Furthermore, secondary flow occurs in the four corners.The state of flow and the intensity of turbulence in the neighborhood of L/W=1.0 in the duct where such an unstationary, complex flow exists and its divergence angle is 12° were investigated and concluded.

202 ヘリウム−空気置換流の流速分布計測および可視化

In the duct having a large divergence angle of square cross section, a slight difference of state of flow occured in the neighborhood of throat wall surface at the upstream inlet and in its four corners grows rapidly at the inlet of divergence duct and makes the entire flow in the duct not uniform unsteady flow. Also in the case of a rapid velocity of flow, a separation from the wall surface occurs, however, the state of separation is different in the corners and the center of wall surface. A reversed stream occurs in the place where the separation takes place. Furthermore, secondary flow occurs in the four corners.The state of flow and the intensity of turbulence in the neighborhood of L/W=1.0 in the duct where such an unstationary, complex flow exists and its divergence angle is 12° were investigated and concluded.