Showing papers on "Beam (structure) published in 1969"

Molecular Beam Reactive Scattering Apparatus with Electron Bombardment Detector

Abstract: A crossed beams apparatus for study of thermal energy neutral-neutral reactions is described. The detector comprises a high efficiency (∼0.1%) electron bombardment ionizer, quadrupole mass filter, scintillation ion counter, and gated scalers synchronized with the beam modulation. The ionizer is nested within three chambers, each pumped by a separate ion pump and the innermost attached to a liquid nitrogen trap. The design is such that molecules which pass through the ionizer without being ionized fly on into another differentially pumped region before hitting a surface. The entire detector unit, including pumps and trap, is mounted on a rotatable platform (angular range ∼140°) which forms the lid of the scattering chamber. The beam sources also comprise modular units, mounted in differentially pumped side chambers which insert into ports in the scattering chamber. Angular distributions of reaction products have been measured for several reactions of Cl, Br, or D atoms with halogen molecules or hydrogen halides. Product velocity distributions have also been measured by time of flight for some of these reactions. In most cases, the partial pressure of interfering background species in the ionization region was ⪝ 10−15 Torr, and satisfactory data could be obtained with reactive scattering signals of a few counts per second.

Gaussian light beams with general astigmatism.

Abstract: This paper considers the propagation and diffraction of coherent light beams through nonorthogonal optical systems such as sequences of astigmatic lenses oriented at oblique angles to each other. The fundamental (gaussian) mode has elliptical light spots in each beam cross section and ellipsoidal (or hyperboloidal) wavefronts near the axis. It is found that the orientation of the light spot differs from that of the wavefront, and changes continuously by as much as pi radians as the beam propagates through free space. A theory of these general astigmatic beams is given and simple experimental observations are described. The coupling factor between two such beams is also given.

Probing of Acoustic Surface Perturbations by Coherent Light

Abstract: The need for sensitive methods of detection and visualization of acoustic surface perturbations has grown with the increasing interest in such fields as acoustic holography, ultrasonic surface wave devices, and acoustic trapped energy resonators. One very sensitive detection method utilizes a coherent light beam as a probe for locally measuring phase and amplitude of the acoustic field. Several variants of this technique are possible, based on measuring phase, deflection, wave front curvature, and spatial frequency content of the reflected beam. Each one of these variants may be combined with a scanning motion of the beam in order to visualize the entire sound field. This paper will attempt to survey the present state of the art and compare the different techniques on the basis of their sensitivity and applicability to specific requirements.

Effect of turbulent fluctuations in an optically active fluid medium.

Abstract: The effect of a beam traversing an optically active medium of turbulent fluctuations of the index of refraction in the medium is investigated theoretically. The general far-field case is solved by integration of the wave equation with both gain and fluctuations of the index refraction, simplified by neglecting the Laplacian of the fluctuating part of the electric field and one of the time derivatives. The far-field diffraction pattern is identical to that for a nonactive medium. For small to moderate extinction there is a loss of power from the coherent beam but only a slight change in the diffraction pattern, accompanied by wide-angle incoherent scattering. For high-gain cases it is possible to have the extinction coefficient less than the gain, but with complete extinction of the coherent beam and a large incoherent scattering pattern. The use of a more realistic turbulence spectrum than previously used has led to the discovery of a second branch in the resolution curve, in which the resolution far exceeds the previously given "limiting resolution" as the aperture size is increased beyond a certain limit, and approaches the diffraction pattern based on the aperture, although there may be considerable attenuation in the intensity in the diffraction pattern of the coherent beam. These results are applicable, for example, to the use of large aperture optics in turbulene wind tunnels.

Numerical Simulation of Warm Two‐Beam Plasma

Abstract: One‐dimensional numerical simulation of plasmas consisting of two unequal warm beams has shown flattening of the small beam and, in most cases, a strong single mode structure at about the wavelength of largest linear growth rate, accompanied by an eddylike arrangement of trapped particles in phase space. The total electrostatic field energy first increases at the linear growth rate and then, after saturating abruptly, decreases at about the same rate to an intermediate level where a much slower decay begins.

Foamed plastic concrete form with fire resistant tension member

Abstract: A self-supporting concrete form of foamed polymeric material to be left in place to provide insulation for a wall the form having two side walls joined by transverse tension members of sheet metal or other thin fire resistent material. The tension members are embedded in projections provided on inner faces of the two walls to provide substantially cylindrical vertically disposed cavities for concrete. The upper and lower edges of the tension members and projections are inwardly spaced from associated edges of the two side walls so that a horizontally disposed concrete beam will also be provided when the form and adjacent similar forms are filled with liquid concrete.

Two nonlinear beams with definitions of ductility

Abstract: TWO MATHEMATICAL MODELS OF NONLINEAR BEAMS WHICH CAN BE USED TO REPRESENT THE GIRDERS AND COLUMNS OF A NONLINEAR MULTISTORY STRUCTURE ARE DESCRIBED AND COMPARED. ONE BEAM MODEL IS LIMITED TO BILINEAR BENDING MOMENT-END ROTATION HYSTERETIC CHARACTERISTICS. THE OTHER MODEL CAN HAVE DIFFERENT CURVILINEAR AND BILINEAR HYSTERETIC CHARACTERISTICS AT EACH END. THREE DIFINITIONS OF DUCTILITY FACTOR ARE MADE AND APPLIED TO YIELDING BEAMS. THESE TYPE OF BEAM MODELS CAN BE USED IN THE STUDIES OF THE DYNAMIC RESPONSE OF EARTHQUAKE EXCITED MULTI-DEGREE OF FREEDON YIELDING STRUCTURES. /ASCE/

Multiple internal reflection face-pumped laser

Abstract: A miniaturized face-pumped, face cooled laser device is described wherein wave front distortion is minimized by the passage of a coherent beam of electromagnetic radiation through an elongated, rectangularly cross-sectioned laser body in an offaxial direction to effect multiple total internal reflections of the beam from fluid cooled, parallelly extending faces of the laser body. Because each ray of the coherent beam passes through substantially identical thermal environments during the reflective transmission of the beam through the laser body, the net distortion of the beam wave front is substantially reduced making the laser device particularly suitable for high-repetition rate, Q-switched operation. In a preferred embodiment, the beam is reflectively passed initially through only a portion of the cross-sectional area of the laser body to effect a first order compensation of beam distortion whereupon the beam is folded back one or more times along adjacent untraversed portions of the laser body for a second order compensation of beam distortion by additional averaging of the optical environment observed by the beam.

Fluctuations of a Beam Wave Propagating Through a Locally Homogeneous Medium

Abstract: : General formulations for the fluctuations of a beam wave propagating through a homogeneous or locally homogeneous medium are given in terms of the spectral density of the index of refraction. The amplitude and phase correlation functions and the mean square fluctuations are derived for a homogeneous medium showing the dependence on the radial distance in the transverse plane of the beam. The amplitude and phase structure functions are derived for a locally inhomogeneous medium. The correlation functions and the structure functions do not depend only on the difference coordinate, but they are functions of the radial coordinates in the beam cross section. This particular inhomogeneity, however, is shown to be an analytic continuation of the homogeneous or locally homogeneous case. The mean square amplitude fluctuation for the Kolmogorov's locally homogeneous medium is shown to behave as a plane wave for short distance and then becomes less than that of a spherical wave, and its spectrum is shown to behave as 1/K for large K in contrast with the plane and spherical waves. The spread of the beam radius is shown to be approximately the 8/3 powers of the distance L for small distance and its increase depends on the magnitude of the index of refraction fluctuation. (Author)

On the response of beams to an arbitrary number of concentrated moving masses

Abstract: A theory describing the response of a beam under an arbitrary number of moving masses is developed. The theory is based on the Fourier technique and shows that, for a simply supported beam, the resonance frequency is lower with no corresponding decrease in maximum amplitude when the inertia is considered.

Scoring of materials with laser energy

Abstract: A process in which a groove or score is generated in a thermoplastic substrate. A focused continuous beam of laser light is directed against the substrate and relative motion is applied between the beam and the substrate. The laser beam is generated and focused with suitable optics so that the beam has sufficient energy density to degrade the plastic material. The relative velocity between the beam and the substrate is such that the beam degrades the substrate without cutting through the substrate and thereby forms a groove in the substrate with a bead bordering the groove.

Apparatus using a beam of positive ions for controlled erosion of surfaces

Abstract: A process and apparatus for controllably eroding the surface of hard materials such as fused quartz, glass, metals and ceramics by the bombardment of the positive ions. Focused argon ions accelerated by potentials of up to 120,000 volts and with a constant beam current are controlled in direction to cause surface erosion of a workpiece to accuracies of up to one-one hundredth of a wavelength of green light. The workpiece is moved at a controlled rate in combination with the control of the beam direction to obtain a controlled erosion pattern over the surface of the workpiece. In another embodiment, an intensity modulated beam current is used. An electron beam is directed at the workpiece in a pattern which surrounds the ion beam to prevent the building up of a positive charge on the work surface. The progress of the erosion is observed and measured by an interferometer system. The movement of the ion beam and workpiece can follow a programmed automatic sequence.

Angular Confinement of Field Electron and Ion Emission

Abstract: Three methods of confining the angular dispersion of a field electron beam from 〈100〉 oriented tungsten emitters are investigated; they are (1) thermal‐field buildup, (2) selective work function reduction by zirconium adsorption, and (3) high‐temperature field evaporation. All three methods confine the emission to a beam half‐angle of less than 9° in the dc current range 0.1 to 100 μA. Method (1) results in a ∼50% reduction in beam voltage. Provided that the vacuum level is good (∼10−10 Torr), long and short term current instabilities are negligible for dc current levels below 10 μA at 300°K for each of the emitter end forms investigated. The angular dispersion and beam voltage of a field ion beam can also be reduced by method (1) as described briefly in this paper.

Nonlinear Vibrations of a Beam With Pinned Ends

Abstract: This paper describes theoretical and experimental investigations of the large-amplitude vibrations of a flexible beam simply supported on a nearly rigid base. The beam is designed to minimize most secondary effects, such as transverse shear flexibility, rotatory inertia, and nonlinearities in curvature and in the stress-strain curve. Detailed attention is given to quantitative verification of the assumptions made in deriving the equation of motion. Three different approaches are used to solve the equation: assumed-space mode, assumed-time mode, and Ritz-Galerkin solutions. In the experiments, the beam was base excited. The resonant frequencies and associated strain distributions, modal shapes, and waveforms were measured for various values of initial tension and amplitude ratios (ratio of maximum amplitude to beam thickness) up to 16. Within experimental accuracy, the experimental results verified all of the assumptions made in the analyses. However, no one method of solution resulted in the best predictions of all of the experimentally observed phenomena.

On the Quantization of Line-Drawing Data

Abstract: This paper describes the development of a criterion for the quantization of line-drawing data. The criterion provides a guide for selecting the quantization fineness required to assure that the significant features of given line-drawing data will be preserved in the quantization process. The criterion is based on viewing a line drawing as an elastic beam under flexure and selecting a quantization grid size that is fine enough to permit the line drawing to be represented by a beam of minimum strain energy. In this model, regions of sharp curvature of the line drawing correspond to regions of high strain-energy density of the elastic beam. The smoothest possible curve that can be reconstructed from a quantized representation is the minimum-energy curve that satisfies the constraints of the quantized data.

Molecular-Beam Sources Fabricated from Multichannel Arrays. I. Angular Distributions and Peaking Factors

Abstract: An apparatus for measuring the leak rates and angular distributions of the molecular flux from multichannel sources was constructed. Four types of beam sources were tested: A single capillary, a crinkly foil stack, an electron‐beam milled quartz membrane, and two sources constructed by fiber optics techniques. The leak rates of the sources were compared to the predictions of Knudsen flow. The angular distributions were characterized by a ``peaking factor,'' defined as the ratio of the center‐line beam intensity from the source to that from a cosine emitter of the same total flow rate. The measured peaking factors agreed with the theoretical predictions of free molecule flow at low source pressures and approached the limit for isentropic flow at high source pressures.

Absolutbestimmung der Gesamtanregungsquerschnitte der Edelgase durch Elektronenstoß

Abstract: With an improved Maier-Leibnitz collision chamber absolute values of the total excitation cross sections of the rare gases were measured. The half width of energy distribution in the beam of exciting electrons was approximately 0.7 eV. The results for He and Ne are in reasonable agreement with the excitation functions given by Maier-Leibnitz, if some necessary corrections (especially with regard to contact potentials) are made. Only the cross sections obtained by us are a little smaller. Furthermore the better fine structure yielded more favourable possibilities of comparison with other measurements published so far. The error should not be greater than 30%.

Multibeam laser-jet cutting apparatus

Abstract: A multibeam laser-oxidizer system which optimizes the cutting performance of a laser cutting tool. Two laser beam systems of different focal length are focused on substantially the same area of the material to be cut. The beam of shortest focal length provides a preheat zone with the short depth of focus and small spot size (compared to the second beam) serving to bring the material to a temperature such that a jet of oxidizing gas applied to the heated spot gives rise to the initiation of the cut. The long focal length lens system concentrates the radiant energy of the second beam over a large depth of focus compared to the preheat beam and as a result a uniform cut through a substantial thickness of material is achieved. Details of the lens systems and cutting toolhead are provided together with details of gas flow openings in the cutting tool for supplying both oxidizing and inert shield gases to the cutting area.

A measurement of the cross section for charge exchange in H+-H- collisions

Abstract: The cross section for the charge-exchange reaction H+ +H- -> H+H has been measured, using an inclined-beams technique, over an energy range from 025 to 10 kev (in the frame of reference in which the target H- ion is at rest). A proton beam collides with an H- beam at an intersection angle of 20° and hydrogen atoms formed from proton charge exchange in the above reaction are detected. This technique provides a relative collision energy much lower than the energy of either beam and ensures separation together with efficient detection of the reaction products in each beam after the collision. The measured cross section, which falls from about 21 × 10-14 cm2 at 025 kev to 25 × 10-15 cm2 at 10 kev, is compared with the theory derived by Bates and Lewis in 1955 and three points of discrepancy are identified. At high energies the calculated cross section decreases as E-1/2, whereas the experimental energy dependence is closer to E-1. The experimental cross section is between two and three times larger than the calculation and it shows structure in the region of 1 kev.

Radiant energy inspection system for rotating objects

Abstract: Radiant energy inspection system for rotating objects including means for directing parallel light beams tangentially along diametrically opposite surface locations of the object, each beam being partially intercepted in accordance with the radial displacements of the object surface relative to the beams. Geometric qualities of the object are determined by producing signals representing the unintercepted beam portions and comparing the signals with one another in a predetermined algebraic frame of reference. Eccentricity is indicated by inphase signal variations while surface irregularities are indicated by phase shifted signal variations. Diameter is indicated by the algebraic difference between the signals.

Method and apparatus for controlling an electron beam

Abstract: A square-shaped electron beam is stepped from one predetermined position to another to form a desired pattern on each chip of a semiconductor wafer to which the beam is applied. For each chip to which the beam is applied, the position of the chip relative to a predetermined position is determined and the distance in these positions is utilized to control the position of the electron beam to insure that the desired pattern is formed on each of the chips separately. Furthermore, the position of the beam is periodically checked against a calibration grid to ascertain any deviations in the beam from its initial position. These differences are applied to properly position the beam.

Spatial Growth of Waves in a Beam‐Plasma System

Abstract: An experiment on spatially growing electron plasma waves in a beam‐plasma system is described. The properties of the electron beam and the plasma separately are known from accurate, independent measurements. Using a “test wave” technique, the dispersion of the waves in the presence and absence of the beam and their linear growth rate as a function of frequency were measured. The growth of a spectrum of waves from broad‐band noise and the termination of the growth due to nonlinear effects were observed.

A Crossed‐Beam Apparatus for Investigation of Ion‐Molecule Reactions

Abstract: A crossed‐beam apparatus for the study of ion‐molecule reactions is described. The device can provide information on the velocity and angular spectra of reaction products as well as on the angular displacement between reactant and product ions. It can thus yield data sufficient to provide a detailed characterization of the dynamics of the system studied. Furthermore, the mass selected ion beam is variable in energy from 100 eV down to the critical low energy region of about 1 eV or less. Although the apparatus thus seems to have broader capabilities than previously described beam devices, it is quite small and comparatively inexpensive.

a Tunable Stimulated Raman Oscillator

Abstract: We report the first observation of tunable stimulated Raman emission. A Q‐switched ruby laser was used to excite the A1 symmetry 248‐cm−1 polariton mode in a LiNbO3 crystal. The crystal, at room temperature, was placed in a resonator external to the laser cavity which was tuned to the Stokes frequency. It was possible to vary the Stokes frequency by altering the angle between the pump beam and the axis of the resonator. Stimulated Raman scattering from other polariton modes (152 cm−1, 628 cm−1) which are potentially tunable was observed. We also report the first observation of stimulated anti‐Stokes emission from a polariton mode.