Beam Divergence Angle Research Articles

Omni-Directional Viewing-Angle Switching through Control of the Beam Divergence Angle in a Liquid Crystal Panel

This paper proposes a method of omni-directional viewing-angle switching by controlling the beam diverging angle (BDA) in a liquid crystal (LC) panel. The LCs aligned randomly by in-cell polymer structures diffuse the collimated backlight for the bright state of the wide viewing-angle mode. We align the LCs homogeneously by applying an in-plane field for the narrow viewing-angle mode. By doing this the scattering is significantly reduced so that the small BDA is maintained as it passes through the LC layer. The dark state can be obtained by aligning the LCs homeotropically with a vertical electric field. We demonstrated experimentally the omni-directional switching of the viewing-angle, without an additional panel or backlighting system.

Small-divergence singlemode emitting tapered distributed-feedback quantum cascade lasers

A tapered distributed feedback quantum cascade laser emitting at λ∼8.1 µm is reported. Utilising a tapered waveguide structure with a surface metal grating, the device exhibited singlemode operation over the temperature range of 100 to 214 K, with sidemode suppression ratio >20 dB and a nearly diffraction limited far-field beam divergence angle of 5.4°.

Chaotic microcavity laser with high quality factor and unidirectional output

Here we report lasing action in lima\c{c}on-shaped GaAs microdisks with quantum dots (QDs) embedded. Although the intracavity ray dynamics is predominantly chaotic, high-$Q$ modes are concentrated in the region $\chi > \chi_c$ as a result of wave localization. Strong optical confinement by total internal reflection leads to very low lasing threshold. Our measurements show that all the lasing modes have output in the same direction, regardless of their wavelengths and intracavity mode structures. This universal emission direction is determined by directed phase space flow of optical rays in the open chaotic cavity. The divergence angle of output beam is less than 40 degree. The unidirectionality proves to be robust against small deviations of the real cavity shape and size from the designed values.

Hyperboloid cylinder-plane lens for shaping laser diode array beam

A high coupling efficiency, simple structure refractive lens was designed; a hyperboloid cylinder-plane lens was proposed to reduce the divergence angle of the laser diode array beam in the fast axis direction. Based on the ray-tracing method, the shape of the input refractive surface of the designed lens is determined by numerical analysis, and designed as aspherical profile in one direction. When the beam from source point reaches the input surface of the lens, it is refracted and becomes a parallel output beam in the fast axis direction. The expressions for describing the irradiance behind the lens are also derived.

Investigation on the effect of beam divergence angle upon output waveform based on stimulated Brillouin scattering optical limiting

This paper investigates the effect of beam divergence angle on output waveform based on stimulated Brillouin scattering optical limiting. Output waveforms in the case of different pump divergence angles are numerically simulated, and validated in a Nd:YAG seed-injected laser system. The results indicate that a small pump divergence angle can lead to good interaction between pump and Stokes, and a platform can be easily realized in the transmitted waveform. In contrast, a peak followed by the platform appears when the divergence angle becomes large.

Resolving power of lens‐less low energy electron point source microscopy

Simulations show the resolving power of lens-less low energy electron point source microscopy to be approximately 15 A for electron energies of between 14 and 105 eV. This resolution can be improved to 10 A by employing a composite hologram method. However, these values fall short of predictions of at least 3 A resolution for electron energies in this range because the limited divergence angle of the electron beam had not previously been taken into account. Also shown is that electron coherence from field emitting tips that terminate in a single atom will not limit the resolving power as much as the beam divergence angle. The penetration depth of electrons with energies of between 50 and 100 eV, into biological molecules, was estimated from the inelastic mean free path length to be 25 A . This places an upper limit on the size of biological molecules for which internal structural information can be obtained using low energy electrons.

Design of cascadable optical unit to compress light for light transmission used for indoor illumination

The research team has designed optical structure to be used as tiles on the outsides of buildings for indoor illumination. To cover an entire building, the team has designed optical units to be used together that can compress light and the recommended thickness of units is around 20 mm. The important factor in our design is producing parallel exit beam from our single units. The research team has used two different optical surfaces, saw-toothed and elliptical, and the con-focus principle to design three optical units. The team has designed three types, a saw-toothed unit, an elliptical unit, and a modified elliptical unit. Finally, the team analyzes the efficiency and the beam divergence angle to compare these optical structures. The modified elliptical type offers the best performance because it has higher efficiency of parallel exit beam and higher utilization rate.

Three-Dimensional Simulation of Brownian Motion of Nano-Particles In Aerodynamic Lenses

A computer code for analyzing nano-particle motions in an aerodynamic particle beam focusing system was developed. The code uses an accurate three-dimensional model for the Brownian diffusion of nano-particles in strongly varying pressure field in the aerodynamic lens system. Lagrangian particle trajectory analysis was performed assuming a one-way coupling model. The particle equation of motion used included drag and Brownian forces. The prediction of the 3-D model for penetration efficiency, beam divergence angle, beam diameter and radial cumulative fraction were evaluated and were compared with those of the axisymmetric models. The simulation results showed that for particle diameters less than 30 nm in helium gas, the Brownian force could significantly affect the beam focusing and particle penetration efficiency. Some potential errors in the naive usage of axisymmetric model were discussed. It was shown that the earlier axisymmetric models lead to the incorrect mean square radial displacement of Browni...

Theoretical Study of the Electrostatic Lens Aberrations of a Negative Ion Accelerator for a Neutral Beam Injector

Aberrations due to the electrostatic lenses of a negative ion accelerator for a neutral beam injector and the space charge effect are theoretically investigated. A multi-stage extractor/accelerator is modeled and the aberration coefficients are numerically calculated using the eikonal method, which is conventionally used in electron optics. The aberrations are compared with the radii of a beam core with good beam divergence and a beam halo with poor beam divergence. H- beamlet profile measurements give the 1/e radii of the beam core and beam halo of 5.8 mm (beam divergence angle: 6 mrad) and 11.5 mm (beam divergence angle: 12 mrad), respectively. When the beam divergence angle of the beam core is 5 mrad and the beam energy is 406 keV, the aberrations due to the electrostatic lenses are less than a few millimeters, thus are less than the radii of the beam core and beam halo. The geometrical aberrations due to the space charge effect (negative ion current density: 10 mA/cm2 ), however, are estimated to be much larger than the radius of the beam halo. Although the aperture radii of the grids are not taken into account in this estimation, the results indicate that the space charge effect is an important factor in the aberration or beam halo in a negative ion accelerator.

Quantum cascade lasers with integrated plasmonic antenna-array collimators

We demonstrated in simulations and experiments that by defining a properly designed two-dimensional metallic aperture-grating structure on the facet of quantum cascade lasers, a small beam divergence angle can be achieved in directions both perpendicular and parallel to the laser waveguide layers (denoted as theta perpendicular and theta parallel, respectively). Beam divergence angles as small as theta perpendicular=2.7 degrees and theta parallel=3.7 degrees have been demonstrated. This is a reduction by a factor of approximately 30 and approximately 10, respectively, compared to those of the original lasers emitting at a wavelength of 8.06 microm. The devices preserve good room temperature performance with output power as high as approximately 55% of that of the original unpatterned lasers. We studied in detail the trade-off between beam divergence and power throughput for the fabricated devices. We demonstrated plasmonic collimation for buried heterostructure lasers and ridge lasers; devices with different waveguide structures but with the same plasmonic collimator design showed similar performance. We also studied a device patterned with a "spider's web" pattern, which gives us insight into the distribution of surface plasmons on the laser facet.

Theoretical Study of Directional Emission Enhancement From Photonic Crystal Waveguides With Tapered Exits

We utilize an approach based on the idea of tapering waveguide exits to increase the directional emission of the light waves emitted from photonic crystal waveguides. It is shown that the enhancement of the directional beaming can be achieved under certain tapered configurations due to the interference pattern created at the exit of the waveguide. The output radiation profile is observed with the finite-difference time-domain method and a 75% reduction in the divergence angle of the out-coupled beam is achieved with the modified waveguide ends.

Development of a high-brightness and low-divergence lithium neutral beam for a Zeeman polarimetry on JT-60U

A high-brightness and low-divergence neutral beam is obtained for a Zeeman polarimetry of edge plasmas on JT-60U. The electron density and the pitch angle of the magnetic field line, thus the plasma current density distribution, can be measured by the Zeeman polarimetry using the lithium beam. A thermionic ion source heated by an electron beam is developed in order to obtain the ion beam current extraction over 10 mA. The beam optics is designed after detailed numerical simulation taking the space charge effects into account because a low-divergence angle of the neutral lithium beam leads to a narrow spectrum of the beam emission. It is also necessary to keep the beam radius small for good spatial resolution due to a long beam line of 6.5 m. The newly developed ion gun is operated on a test stand which simulates the diagnostic arrangement on JT-60U. The ion beam current of 10 mA at a beam energy of 10 keV is successfully extracted from the ion source operated at the temperature over 1300 degrees C and focused by Einzel lens. The full width at half maximum radius of the ion beam at the neutralizer is about 9 mm. A sodium vapor neutralizer neutralizes the collimated ion beam fully at the temperature of 300 degrees C. The neutral beam profiles are measured at two locations of the beam line at Z=2.3 m (beam monitor position) and Z=6.5 m (plasma region). The half-width at half maximum radius of the neutral beam of 26 mm and the equivalent beam current of 3 mA with the beam divergence angle of 0.2 deg which is the half-angle divergence are obtained. Those parameters satisfy the requirements of the Zeeman polarimetry. Furthermore, a long pulse extraction with a current of 10 mA and duration of 50 s is attained.

Improving extraction and transport simulations of the superconducting ECR ion source VENUS

A plasma sheath extraction model has been added to the three-dimensional, particle-in-cell (PIC) code WARP in order to simulate the extraction and transport of ion beams from the superconducting ECR ion source VENUS. The WARP code is ideally suited to simulate ECR ion source transport systems since it can handle large particle numbers, multiple species, applied and self fields, and has a powerful PYTHON programming shell that allows the user to easily customize the simulation. The addition of an axially symmetric sheath extraction model for a multi species plasma allows for the simulation of the entire VENUS beam line including extraction. To benchmark this model against experiment we have produced axially symmetric beams from VENUS composed almost exclusively of one ion species. These axially symmetric beams are produced by operating the VENUS source without sextupoles, which confine the plasma radially. In addition we performed single species experiments with the sextupoles energized. These measurements confirm the expected triangular shape of the extracted beam. To simulate asymmetric plasma extraction, a simple approximation using the results of the symmetric extraction model is employed. Comparisons between simulation and experiment for both extraction cases at a beam profile diagnostic device (beam harp) after the extraction and at an emittance scanner after the analyzing magnet are presented. Good agreement in both the size and shape of the beam were found at the beam harp provided the beam is not overfocused to a waist before the harp. Simulation and experiment also show reasonable agreement in beam size and divergence angle when comparing emittance scanner measurements after the analyzing dipole. © 2008 Elsevier B.V. All rights reserved. PACS: 07.77.Ka; 29.25.Ni; 29.27.Ac; 29.27.Eg

Beam collimation of high-power laser diode array with graded-index fiber lens array

Graded-index (GRIN) fiber lens arrays are fabricated from commercial GRIN fibers to collimate a high-power laser diode array. The beam divergence angles are reduced to 4.2 and 14.7 mrad in the fast and slow axes, respectively. The influences of smile and fluctuation in fiber length are discussed. Using an aspherical focal lens system, about 74% power can be launched into a fiber with a numerical aperture (NA) of 0.22 and a core diameter of 400 mu m. (c) 2008 Society of Photo-Optical Instrumentation Engineers.

Fiber-Optic Vibration Measurement for Low Refractive-Index Media Using Wavefront Splitting Interferometry

A fiber-optic vibration measurement technique based on the wavefront-splitting interferometry is presented in this paper. Due to a small divergence angle of Gaussian laser beam emitting from a single-mode fiber, the sensing beam propagating toward the specimen has an incident angle of nearly 90°, so that the reflection coefficient of specimen surface is relatively high even for low-refractive-index materials. In preliminary tests, overhead-projector transparency was used to demonstrate the vibration measurement with our fiber-optic vibration sensor up to 4 kHz. The Young's modulus of the transparency was also determined by using the vibration method, and the result agreed well with that measured by using a conventional testing machine.

Cr,Er:Y2.93Sc1.43Ga3.64O12 Laser Giant Pulse Generation at 2.79μm Using Electro-Optic Q-Switch

We present an electro-optically Q-switched 2.79 μm Cr,Er:Y2.93Sc1.43Ga3.64O12 laser using LiNbO3 Pockels cell and undoped Y3Al15O12 plate polarizer. The optimal delay for triggering the Q-switch with respect to the peak of waveform of the flashlamp is found to be about 120 μs. The minimum pump threshold of 13.2 J is realized using the output coupler of reflectivity 74%. The maximum outputs of 72.3 mJ at 3 Hz and 35.4 mJ at 10 Hz repetition rates are obtained. The minimum pulse width is measured to be 31.9 ns. The far-field divergence angle of the laser beam is about 8.8 mrad. The influence of repetition rates on the output energy is also discussed.

Acceleration of ampere class H− ion beam by MeV accelerator

The H(-) ion accelerator R&D to realize the international thermonuclear experimental reactor neutral beam is ongoing at Japan Atomic Energy Agency (JAEA). The required performance for the prototype MeV accelerator developed at JAEA is 1 MeV, 500 mA (current density of 200 A/m(2)) H(-) ion beam at the beamlet divergence angle of less than 7 mrad. Up to 2005, 836 keV, 146 A/m(2) H(-) ion beam was successfully accelerated as the highest record of the current density at MeV class energy beams. In the present work, high current negative ion beam acceleration test was performed by increasing the beam extraction apertures from 3 x 3 (9 apertures) to 3 x 5 (15 apertures). By fixing the air leak at the source chamber due to backstream ions as well as the improvement of voltage holding capability by a new fiber reinforced plastic insulator ring, the performance of the MeV accelerator was improved. So far, H(-) ion beam of 320 mA was successfully accelerated up to 796 keV with the beam divergence angle of 5.5 mrad. The accelerated drain current including the electron reaches close to the power supply limit for the MeV test facility. The heat flux by the backstream ion during the above beam acceleration was estimated to be 360 W/cm(2). The Cs leakage to the accelerator during the test campaign (Cs total input of 5.0 g) was 0.26 mg (7.0 microg/cm(2)). This is considered to be the allowable level from the viewpoint of voltage holding.

Development of a high efficiency proton source for the Frankfurter-Neutronen-Quelle am Stern-Gerlach-Zentrum

A new version of high efficiency proton source is being developed for Frankfurter-Neutronen-Quelle am Stern-Gerlach-Zentrum, a worldwide unique pulsed neutron source. The injector will provide dc proton beam currents of 200 mA at 120 keV with a beam divergence angle of less than 50 mrad. The new design consists of a plasma generator with a multiple filament arrangement and a compact pentode extraction system. The beam will be extracted from a seven hole outlet electrode. Great efforts are made to achieve an adequate operation time (~3 days) of the source as well as to obtain high reliability during that operation period with less than 1 V breakdowns per hour. The following article will present the current status of the proton source development including beam formation simulations with IGUN.

Differential schlieren-interferometry with a simple adjustable Wollaston-like prism

An adjustable Wollaston-like prism is characterized for use in shearing- and differential schlieren-interferometry with laser and white-light illumination. We demonstrate that a polycarbonate prism under mechanical loading behaves identically to Wollaston's classical birefringent beam splitter. A linear relationship is found between the pure bending moment applied to the polycarbonate prism and the resulting light-beam-divergence angle. The utility of this prism in shearing-interferometry is shown by using it in place of the knife-edge in small and large schlieren optical systems. It is inexpensive to fabricate, and it yields adjustable beam-divergence angles over a range of at least 0-24 arc min.

A novel butt-joint scheme for the preparation of electro-absorptive lasers

A 1.55 µm InGaAsP/InGaAsP multiple-quantum-well electro-absorption modulator (EAM) monolithically integrated with a distributed feedback laser (DFB) diode has been realized based on a novel butt-joint scheme by ultra-low metal-organic vapour phase epitaxy for the first time. The threshold current of 25 mA and an extinction ratio of more than 30 dB are obtained by using the novel structure. The beam divergence angles at the horizontal and vertical directions are as small as 19.3° × 13°, respectively, without a spot-size converter by undercutting the InGaAsP active region. The capacitance of the ridge waveguide device with a deep mesa buried by polyimide was reduced down to 0.30 pF.