Showing papers on "Beam (structure) published in 1971"

Optical Levitation by Radiation Pressure

Abstract: The stable levitation of small transparent glass spheres by the forces of radiation pressure has been demonstrated experimentally in air and vacuum down to pressures ∼1 Torr. A single vertically directed focused TEM00‐mode cw laser beam of ∼250 mW is sufficient to support stably a ∼20‐μ glass sphere. The restoring forces acting on a particle trapped in an optical potential well were probed optically by a second laser beam. At low pressures, effects arising from residual radiometric forces were seen. Possible applications are mentioned.

RMS Envelope Equations with Space Charge

Abstract: Envelope equations for a continuous beam with uniform charge density and elliptical cross-section were first derived by Kapchinsky and Vladimirsky (K-V). In fact, the K-V equations are not restricted to uniformly charged beams, but are equally valid for any charge distribution with elliptical symmetry, provided the beam boundary and emittance are defined by rms (root-meansquare) values. This results because (i) the second moments of any particle distribution depend only on the linear part of the force (determined by least squares method), while (ii) this linear part of the force in turn depends only on the second moments of the distribution. This is also true in practice for three-dimensional bunched beams with ellipsoidal symmetry, and allows the formulation of envelope equations that include the effect of space charge on bunch length and energy spread. The utility of this rms approach was first demonstrated by Lapostolle for stationary distributions. Subsequently, Gluckstern proved that the rms version of the K-V equations remain valid for all continuous beams with axial symmetry. In this report these results are extended to continuous beams with elliptical symmetry as well as to bunched beams with ellipsoidal form, and also to one-dimensional motion.

Lateral Displacement of Optical Beams at Multilayered and Periodic Structures

Abstract: Many planar structures, including multilayered media and periodic configurations of the optical-grating type, are capable of supporting an electromagnetic field of the leaky-wave form. By exciting this field, an incident light beam transfers a portion of its energy into the leaky-wave structure; after being guided longitudinally for a certain distance along the structure, this energy is leaked back to form part of the reflected beam. Owing to the longitudinal energy flow, the complete reflected beam exhibits a lateral displacement that appears either as a forward beam shift, similar to the Goos-Hanchen effect along a single dielectric interface, or as a backward beam shift, which has not been identified before. By deriving a general expression for the field excited by a gaussian light beam incident upon a leaky-wave structure, we find that the reflected beam may undergo a lateral displacement of the order of the beam width; the magnitude of this beam shift may therefore be much larger than the maximum shift produced at a single dielectric boundary. In the case of periodic structures, all of the higher-order diffracted beams are shifted laterally whenever the specularly reflected beam is displaced. The dependence of the lateral displacement on the beam width, the angle of incidence, and the leakage distance is examined in detail and the relevance of the beam shift to optical-beam couplers is discussed.

Beam Behavior within the Nearfield of a Vibrating Piston

Abstract: A numerical investigation of the nearfield region of a vibrating piston was conducted. While existing literature is not exactly clear about how close to a transducer a regular beam pattern is formed, the results of this investigation show the limits of operation one can expect. From one interpretation of literature, a −3‐dB beam with a minimum spot size equal to the transducer diameter would be expected to form beyond an axial distance z = 3.89 a2/λ. This investigation shows that such a beam forms at z = 0.75 a2/λ and has a minimum spot size equal to one‐quarter the transducer radius. These results are verified for transducers with a/λ's ranging from 1 to 20 and can be extended with confidence to higher a/λ's. Similar results are also obtained for −1.5‐, −4.5‐, −6.0‐, −7.5‐, −9.0‐, −10.5‐, and −12‐dB beams.

Lateral Displacement of a Light Beam at a Dielectric Interface

Abstract: The lateral (Goos–Hanchen) shift of a gaussian light beam incident from a denser medium upon the interface to a rarer medium is investigated by means of a rigorous integral representation comprising a continuous plane-wave spectrum. By applying a Fresnel approximation to that integral, we derive the lateral displacement for angles of incidence that are arbitrarily close to the critical angle of total reflection. Our results show that, in general, the lateral displacement is a function of the beam width, as well as the incidence angle; the classical expression appears as a limit case which holds only for large beam widths and for incidence angles that are not too close to the critical angle. An analysis of our expression for the beam shift reveals that, as the incidence angle approaches the critical angle of total reflection, the beam shift approaches a constant value that is strongly dependent on the beam width, in contrast to the classical expression, which predicts an infinitely large displacement; we also find that the maximum lateral displacement occurs at an angle that is slightly larger than the critical angle. Numerical results are presented in terms of normalized curves that are applicable to a wide range of realistic beams.

Possible Emittance Increase through Filamentation Due to Space Charge in Continuous Beams

Abstract: The study of oscillations which can take place in a beam under space charge conditions has been extended to other distributions than the one described by Kapchinsky and Vladimirsky (K. V.) in 1959. Two sets of equations similar to the ones they established can be written provided axis and emittance values are replaced by rms expressions applicable to any type of distribution. In case of a non K. V. distribution, the comparison of these sets gives differential equations relating the rms emittances to correcting terms which depend on the charge distribution inside the beam. Such equations can be used to interpret some rms emittance increases observed either with a mismatch in a smooth focusing channel or with a matched beam in an AG focusing system.

Coupling Beams of Reinforced Concrete Shear Walls

Abstract: The behavior of short and relatively deep reinforced concrete beams, which occur in shear walls of multistory structures, and the damage or failure of which has been observed in recent earthquakes, is examined. Experimental and analytical studies indicate that their ultimate flexural capacity is reduced by large shearing forces, even if a diagonal tension failure is prevented by adequate web reinforcement. After diagonal cracking, the distribution of internal forces radically differs from that observed in beams of normal proportions. The flexural reinforcement is found to be in tension in areas where compression is expected, and this affects the beam's ductility. Shear deformations of diagonally cracked coupling beams greatly overshadow those causd by flexure. With the aid of a model of the cracked beam its stiffness can be approximated. This satisfactorily agrees with observations which indicate that the stiffness after cracking is less than 20% of the stiffness of uncracked coupling beams.

Penetration of fast hydrogen atoms into a fusion reactor plasma

Abstract: The depth of penetration of fast hydrogen atoms into a fusion reactor plasma, before they become ionized and held by the magnetic field, is of importance in connection with the heating and refuelling of such a plasma. Here the experimental cross-sections for the important collision processes are reviewed and analytic expressions are formed which describe the data reasonably well.The ion and electron energy distributions to be expected in both toroidal and mirror reactors are used, with the analytic expressions for the cross-sections, to calculate rate coefficients. The plasma thickness T for an 1/e reduction in intensity of the atom beam is then obtained as a function of beam energy and plasma temperature over the range 0.1 to 2000 keV (D+, Do). As an example a 1 MeV deuterium atom beam entering a toroidal reactor plasma has T=1.7×1016 and 2.5×1016cm−2 for plasma temperatures of 1 and 100 keV, respectively.

The weak beam technique as applied to the determination of the stacking-fault energy of copper

Abstract: The weak beam technique is used to obtain a value for the stacking-fault energy of copper. The observed partial dislocation image spacings are compared with many-beam computational models and it is demonstrated that anisotropic elasticity theory breaks down for small partial dislocation spacings in copper.

Light scanning and printing system

Abstract: A light scanning system of controlled spot motion variation perpendicular to the direction of scan utilizing a rotating mirror and two cylindrical or toroidal lenses positioned relative to the rotating mirror to allow increased nominal axis of rotation to facet angular tolerances while maintaining a distinct non-overlapping line scan. Specifically, for one application the axis of rotation of the mirror is orthogonal to the plane formed by the incoming and reflected beam from the mirror. The first cylindrical or toroidal lens, which has little or no power in the scan plane, focuses the incoming beam in the azimuth perpendicular to the scan onto the mirror while the second cylindrical lens acts as a beam configurer to configure the beam to substantially collimated shape while directing it towards a spherical lens for focusing onto an image plane.

Scattering of Light from a Rotating Ground Glass

Abstract: We report some experimental results concerning the statistical properties of a light beam scattered by a rotating ground glass with average-size inhomogeneities of approximately 1 μm. Photocount statistics measured at different scattering angles and for different angular velocities of the ground glass have confirmed the known result that the scattered-light amplitude is a stochastic gaussian variable. The Bose–Einstein nature of the photocount statistics has been verified with an accuracy of a few parts per thousand. Self-beating measurements on the scattered light of a He–Ne laser in a TEM00 configuration have shown that the power spectrum is a gaussian function of the frequency. The dependence of its half-width on the angular velocity of the ground glass and on the focal length of the lens that focuses the beam on the scattering surface has been measured. The experimental results agree very closely with our theoretical predictions.

Plasma Heating by High-Current Relativistic Electron Beams

Abstract: A mechanism is proposed for the heating of a plasma with a high-current relativistic electron beam which makes essential use of the plasma return current induced by the beam. From overall energy conservation it is concluded that a large fraction of the beam energy is converted into plasma thermal energy. For reasonable parameters the heating occurs through ion sound turbulence generated by the plasma return current.

Laser system for microsurgery

Abstract: A beam of infrared energy from a CO2 laser operating in its lowest order spatial mode is passed through a converging lens and directed to an operating site by a mirror or beam splitter. In order to locate the invisible focused spot of infrared energy a beam of visible light from a He-Ne laser is introduced coaxially into the path of the CO2 laser beam by a removable mirror. In another embodiment the He-Ne beam is passed through a beam splitter to form two parallel channels focused by microscope objectives on the input ends of respective fiber optic light guides. A rotating chopper disc is positioned in front of the light guides to alternately block and pass light in each channel. The other ends of the light guides are connected to marker projectors located above the beam splitter for the CO2 beam, but just out of the field of view of an overhead operating microscope. A lens and mirror system in each projector focuses the visible light through the beam splitter onto the focal point of the CO2 beam at the operating site. If the intended site is above or below the CO2 beam focal point, spaced red dots alternating at the frequency of the chopper disc will appear to the viewer through the microscope, indicating the need for further adjustment. Perfect adjustment is indicated by a single non-flashing dot.

Molecular Beam Study of the K+I2 Reaction: Differential Cross Section and Energy Dependence

Abstract: A molecular beam study of the reactive and nonreactive scattering of a velocity‐selected K beam crossed with a thermal I2 beam is described. Velocity analysis yielded the recoil velocity‐angle distribution of product KI flux. The energy dependence of this flux distribution was determined from measurements at several incident K beam velocities, corresponding to a range of collision energies Ē from 1.9 to 3.6 kcal/mole. Computational methods were developed to extract the c.m. differential reactive cross section functions (angular and recoil‐energy distributions) from the laboratory data. In accord with previous literature on related systems, the reactive cross section is “forward peaked” and most of the exoergicity (some 40 kcal/mole) goes into internal excitation of the KI product. However, there is also significant KI scattering at wide angles and with large recoil energies. The c.m. angular and recoil‐velocity distributions are some‐what coupled (i.e., nonfactorizable). An increase in Ē from 1.9 to 3.6 kcal/mole produces only a slight change in the shape of the c.m. differential cross section, accompanied by a small decrease (< 20%) in the magnitude of the reaction cross section. Measurements were also made on the angular and velocity distributions of the nonreactively scattered K over the same energy range.

Return Current Induced by a Relativistic Beam Propagating in a Magnetized Plasma

Abstract: The propagation of a high current relativistic beam in a cold magnetized plasma is investigated using a model developed by Hammer and Rostoker for the unmagnetized case. In this model, the beam electrons are assumed to be undeflected from their zero‐order orbits and the fields associated with the beam are switched on at time t = 0. The return current induced in the plasma is calculated as a function of beam and plasma parameters. It is demonstrated that the return current does not extend indefinitely but dies away inversely as the distance from the head of the beam with a characteristic length Ln = v0τa2/λE2, where v0 and a are the beam velocity and radius, τ is a phenomenological momentum relaxation time for the plasma electrons, λE = c/ωp, and ωp is the plasma frequency of the plasma electrons. When the beam is injected either parallel or perpendicular to a static magnetic field B0, it is found to be magnetically neutralized by a return current over a length of order Ln if a2/[λE2(1+Ω2/ωp2)]≫1, where Ω ...

Method for scanning mask forming holes with a laser beam

Abstract: A technique of constructing a plurality of holes in sheet material by scanning a coherent laser beam across holes in a mask overlaying said material. The use of a stream of gas coaxially aligned with said coherent light beam is also disclosed. A special technique is included for making one or more holes in a non-homogeneous particulate sheet material having finely divided particles held together by a binder, such as green (unbaked) ceramic, with the use of a coaxial coherent light beam and gas pressure stream.

Laser welding plastic tubes

Abstract: A method of welding a plastic end member to an unstepped, plastic tubular body which comprises positioning the end member within the body and then irradiating the area to be welded with a laser beam for a specified time sufficient to achieve the desired weld while simultaneously imparting relative rotational motion between the beam and the area to be welded.

Acoustic Surface‐Wave Beam Diffraction on Anisotropic Substrates

Abstract: The diffraction of any distribution can be discussed in terms of its constituent Gaussian modes. Simple design formulas are developed from a two‐dimensional diffraction theory in order to characterize Gaussian beam diffraction in terms of three readily determined anisotropic propagation coefficients. The relationship between these coefficients and known anisotropic propagation phenomena is explored. Beam steering, diffraction, and focusing effects are discussed in some detail. Attention is drawn to two particular effects: autocollimation and ``negative'' phase front curvature. Situations in which both occur in practice are discussed. The former should play a significant role in acoustic matched filter design. A cylindrical transducer is shown, within limits, to be an optimum structure for obtaining a single acoustic beam convergence, even in the presence of beam scattering. The parabolic diffraction theory is applied to the design of an experimental anisotropic focusing system.

One-dimensional model of relativistic electron beam propagation

Abstract: Numerical and analytic methods have been used to investigate the propagation of a relativistic electron beam through a grounded conducting plane into a region which either is vacuum or contains a neutral gas The one-dimensional model used represents the behaviour of real beams whose radius is large compared with c/ omega b (the ratio of the speed of light to the plasma frequency corresponding to the beam density) In the vacuum case, the beam does not propagate but a moving potential well forms which could provide a mechanism for ion acceleration When neutral gas is present, the beam propagates with a speed which depends on the rate at which the gas is ionized by collisions with the beam electrons

The application of non-systematic many-beam dynamic effects to structure factor determination

Abstract: A method for utilizing non-systematic many-beam dynamic effects for determination of accurate relations between Fourier potentials is described The effects which are used can be understood and described in terms of three-beam interactions; although quantitative evaluation is based on more interacting beams The effects are most readily observed in Kikuchi patterns; experimental patterns from silicon are used as an example

Means for suppressing ground clutter in airborne radar

Abstract: Method and means for detecting both long and short range weather targets in the presence of ground clutter in which a receive antenna beam is steered from a first generally elevated beam position to a second generally horizontal beam position in accordance with a beam steering program.

Non-contacting measuring probe

Abstract: A non-contacting optical probe capable of giving a continuous reading of the distance from a given reference to a contoured surface. A collimated beam is projected on a first optical axis to the surface to be measured. A second optical axis extends from the surface to be measured at an angle to the first optical axis. When the projected beam meets the surface at the point of intersection of the second optical axis, a reflected beam passes along the second optical axis to a sensor which detects this beam. The projected light beam and its optical axis are caused to reciprocate at an angle to the surface, this being accomplished by passing the collimated beam through a rotating prism. The prism is a regular polygon. A second sensor detects the rotation of the prism. The distance to the surface being measured is detected as the interval of time between the detecting of the prism position by the second sensor and the detecting of the reflected light beam by the first sensor.

Reinforced concrete beams under load reversals

Abstract: A SERIES OF 12 REINFORCED CONCRETE CANTILEVER BEAMS WERE SUBJECTED TO REVERSALS OF OVERLOAD TO DETERMINE THE EFFECT OF LOAD HISTORY ON THE STRENGTH, DUCTILITY, AND MODE OF FAILURE OF THE BEAMS, THE RESULTS SHOWED THAT THE BEHAVIOR OF THE SPECIMENS UNDER LOAD REVERSAL WAS INFLUENCED PRIMARILY BY SHEER. CHANGES IN BEAM GEOMETRY OR LOAD HISTORY WHICH REDUCED THE SHEAR FORCE OR INCREASED THE SHEAR CAPACITY OF THE BEAM SIGNIFICANTLY INCREASED THE ENERGY ABSORBING CAPACITY AND THE NUMBER OF CYCLES TO FAILURE. /AUTHOR/

Dynamics of Pulsed High Current Relativistic Electron Beams

Abstract: Pulsed electron beams are formed by the slow charge of a pulse forming network (microseconds to D. C.) and the fast discharge (10 - 100 ns) onto a field emission diode. The resultant beams of kiloamps to megamps at hundreds of keV to ten MeV are passed through a window into the drift region. Ionization in the drift section allows the beam to be confined by its own magnetic field. Secondary electron currents in the plasma tend to neutralize this effect, Recent work on guiding intense beams with auxiliary fields has utilized applied Bz and B? (z-pinch) fields. Application of these beams extends from shock studies to ion acceleration.

Growth rates and stability limits for beam--plasma interaction.

Abstract: A treatment is given of the one‐dimensional problem of beam‐plasma interaction, including the effects of plasma and beam thermal velocities and momentum transfer collisions in the plasma. The conditions under which the Landau damping due to the plasma is negligible are first investigated. Neglecting this damping, a weak‐beam approximation to the dispersion relation is derived, and conditions for its validity are established. Expressions are derived for the maximum temporal and spatial growth rates in the limits of cold and hot beams, and few and many collisions. The growth rates given by the weak‐beam approximation are compared with those calculated from the full dispersion relation. The transition from a cold to a hot beam is discussed in terms of the topology of the roots of the dispersion relation, and also in terms of the location of the phase velocities of the most unstable waves relative to the bump in the distribution.