Showing papers on "Beam (structure) published in 1977"
TL;DR: In this paper, a simple cavity design for nitrogen-laser-pumped dye lasers is presented, achieving a linewidth of 0.08 cm−1 with a single dispersive element and without any intracavity beam expansion.
Abstract: A new simple cavity design for nitrogen‐laser‐pumped dye lasers is presented. Narrowband operation is achieved with a single dispersive element and without any intracavity beam expansion. The dispersive element is a diffraction grating used near grazing incidence with an additional mirror, instead of the usual Littrow arrangement. The large angular dispersion obtained results in a linewidth of 0.08 cm−1. The typical peak power obtained is 4 kW with 50 kW in the pump beam. Calculations of linewidth based on single‐pass estimates are presented and are found to be in good agreement with experimental results.
235 citations
TL;DR: In this article, a moment theory for the nonlinear quasi-optical equation with saturation is applied to self-trapped laser beams in plasma for the ponderomotive nonlinearity.
Abstract: A moment theory for the nonlinear quasi‐optical equation with saturation is applied to self‐trapped laser beams in plasma for the ponderomotive nonlinearity. The results differ quantitatively from those obtained form the paraxial ray theory but do agree qualitatively in that there is a minimum beam radius of order c/ωp, a threshold ’’critical’’ power, no upper limit to the power that can be transmitted, and the self‐trapped beams are stable.
177 citations
TL;DR: In this paper, the mode II fracture of western hemlock wood beams was studied and a finite element analysis was performed to predict the ultimate loads for end-cracked, large-size beams cut from dimension lumber.
169 citations
TL;DR: In this paper, a volume phase hologram recording in pure LiNbO 3 crystals with applied electric field E ≈ 5 kV/cm is accompanied by considerable intensity redistribution of the writing beams by transient energy transfer.
166 citations
TL;DR: In this paper, a diffusion model of atomic mixing by ion bombardment is presented, where the mixing is assumed to have its basis, as does sputtering, in the collision cascades generated by the primary beam.
Abstract: Calculations based on the diffusion model are presented of atomic mixing by ion bombardment. This mixing is assumed to have its basis, as does sputtering, in the collision cascades generated by the primary beam. Sharp interfaces within a target are seen to be smoothed by ion bombardment. Mixing may place fundamental limits on the resolution of ion microprobes.
144 citations
TL;DR: In this article, the photofragment spectrum of C2H5ONO at 28 810 cm-1 has been obtained by crossing a beam of brief pulses of polarized laser light with the beam of C 2H5O in a collision-free environment.
Abstract: The photofragment spectrum of C2H5ONO at 28 810 cm–1 has been obtained by crossing a beam of brief pulses of polarized laser light with a beam of C2H5ONO in a collision-free environment. The photodissociation products are C2H5O and NO. The angular distribution of fragment intensities peaks in a direction orthogonal to E, the electric vector of the light, indicating that the transition moment lies perpendicular to the bond that breaks. The high degree of angular anisotropy shows that the average lifetime in the upper state is short compared to a molecular rotational period, being at most 2 × 10–13 s. The distribution of fragment translational energies has also been measured, and shows that the most probable total fragment translational energy is 6000 cm–1, or about 36 % of the energy in excess of that needed to break the O—N bond. The most probable fragment total internal energy is 10 400 cm–1. The energy distribution can be matched by a simple modified impulsive model for the molecular dynamics of the photodissociation.
139 citations
TL;DR: In this paper, a transverse displacement inteferometer (TDI) was used to monitor the transverse motion of the rear surface of a ycut quartz target plate in a plate-impact experiment.
Abstract: A new transverse‐displacement inteferometer (TDI) is described. This interferometer makes use of intensity variations of a beam obtained by superposition of two beams diffracted symmetrically from a diffraction grating copied onto a plane surface. The TDI is used to monitor the transverse motion of the rear surface of a y‐cut quartz target plate in a plate‐impact experiment. For this application, a 200‐line/mm grating is copied onto the rear surface of the target plate. The normal motion of the rear surface is monitored by means of a standard Michelson interferometer in which the zeroth‐order diffracted beam is used as the beam reflected from the moving mirror. The transverse motion is monitored simultaneously by means of a TDI employing the two fourth‐order diffracted beams, with a resulting sensitivity of 0.625 μm per fringe. The recorded motion confirms the predicted features of two coupled elastic waves, each involving both normal and transverse motion.
130 citations
TL;DR: The helical wiggler as mentioned in this paper is a device in which relativistic electrons pass through a transverse magnetic field whose direction revolves with distance along the beam axis, and the question is whether this device can be incorporated into a storage ring without destroying the circulating beam.
Abstract: The ’’helical wiggler’’ is a device in which relativistic electrons pass through a transverse magnetic field whose direction revolves with distance along the beam axis. In this paper we discuss the electron orbits in this device. The field patterns and necessary current distributions are established. Finally, the question is treated as to whether this device can be incorporated into a storage ring without destroying the circulating beam. It is concluded that there is reason to expect satisfactory performance from helical wigglers in storage rings.
114 citations
TL;DR: In this paper, the behavior of a Gaussian ultrasonic beam incident on a liquid-solid interface at the Rayleigh angle has been studied in some detail, and good agreement is obtained between experimental results and the theory of Bertoni and Tamir.
Abstract: The behavior of a Gaussian ultrasonic beam incident on a liquid‐solid interface at the Rayleigh angle, the angle at which surface waves are excited on the interface, has been studied in some detail. The reflected beam is displaced in the manner predicted by Schoch; however, the ’’Schoch displacement’’ in general is too large. Good agreement is obtained between experimental results and the theory of Bertoni and Tamir, which assumes that the incident beam couples resonantly into a leaky surface wave at the Rayleigh angle and that the energy reradiated from this leaky surface wave interferes with specularly reflected energy. The propagation distance of the ultrasonic beam is explicitly included in describing the ultrasonic wave reflection at the Rayleigh angle.
109 citations
TL;DR: The absolute specular reflectance of flat mirrors was obtained as a function of the reflected beam width from 1 mrad to 17 mrad using a bidirectional reflectometer.
108 citations
TL;DR: The essential focal beam dimensions and temporal coherence of the sound wave have been preserved at this frequency after transmission through this particular skull, indicating that no adult human skull should have a higher attenuation value at a frequency of 500 kHz than this skull shows at 1 MHz.
Abstract: An intense focused ultrasonic beam was used in the transkull transmission mode to produce focal thermal “lesions” in a lucite block. This result was accomplished with a 1 MHz beam transmitted through an excised adult human skull section which had been shown by low intensity measurements to have 13 dB attenuation of sound pressure at this frequency. The essential focal beam dimensions and temporal coherence of the sound wave have been preserved at this frequency after transmission through this particular skull. Other studies indicate that no adult human skull should have a higher attenuation value at a frequency of 500 kHz than this skull shows at 1 MHz.
TL;DR: In this article, a study of the natural vibrations of a Timoshenko beam on a Pasternak-type foundation is presented, where the effects of rotary inertia, shear deformation, and foundation constants on the natural frequencies of the beam are analyzed.
TL;DR: In this paper, a colliding-beam method was used to find two resonances in the photodetachment of electrons from H/sup -/. A nitrogen laser beam is directed at variable angle across the 800-meV H/Sup -/ beam at the Clinton P. Anderson Meson Physics Facility (LAMPF), resulting in a center-of-mass photon beam wavelength which is continuously tunable from the visible to the vacuum ultraviolet.
Abstract: We have used a colliding-beam method to find two resonances in the photodetachment of electrons from H/sup -/. A nitrogen laser beam is directed at variable angle across the 800-meV H/sup -/ beam at the Clinton P. Anderson Meson Physics Facility (LAMPF), resulting in a center-of-mass photon beam wavelength which is continuously tunable from the visible to the vacuum ultraviolet. Our preliminary measurements of the two resonances observed near 11 eV agree well with theoretical predictions within our experimental resolution of 10 meV. (AIP)
TL;DR: In this paper, a two-dimensional quadrupole field has been calculated to second order in input position, angle, and energy, and the use of this field as an energy analyzer and as an achromatic deflector is described.
Abstract: The deflecting properties of a two‐dimensional quadrupole field have been calculated to second order in input position, angle, and energy The use of this field as an energy analyzer and as an achromatic deflector are described The calculated dispersion, which is 845% that of of a 127° analyzer of equal angular aberration, has been confirmed by measurement on a deflector designed and built for merging an ion beam with a laser beam This deflector can bend a 3‐kV ion beam of 2‐mm diameter, ±2‐mrad angular spread, and 1‐eV FWHM energy spread by 90° without causing a detectable increase in the diameter or angular spread of the beam
TL;DR: In this paper, the authors studied the process of pinch formation in large aspect ratio diodes by means of streak photography and time-resolved x-ray detectors and found that the collapse velocity depends on the type of material in the top 1 μm layer of the anode.
Abstract: The process of pinch formation in large aspect ratio diodes has been studied by means of streak photography and time‐resolved x‐ray detectors. A tight pinch is formed at the anode center by a collapsing thin hollow electron beam emitted from a hollow cathode. The collapse velocity depends, amongst other things, on the type of material in the top 1 μm layer of the anode. In the suggested model it is assumed that the anode plasma is created from gases released from the surface layer of the anode by the heating action of the beam. These gases are ionized by avalanche breakdown aided by primary, backscattered, and secondary electrons. Ions emitted from this plasma modify the electron trajectories in the diode leading to a radial collapse of the hollow electron beam. The observed monotonic dependence of the collapse velocity on the atomic number of the anode material can be explained by the smooth dependence on Z of both the specific heat and the electron backscatter coefficient. In the case of high‐Z anodes the ion expansion time is calculated and shown to be the factor limiting the collapse velocity. The use of thin foils to speed up the collapse rate is suggested. Detailed experimental data are presented.
TL;DR: In this article, an opto-acoustic method for a precise determination of absolute fluorescence quantum efficiencies in solutions is described, using an intensity modulated beam of an argon ion laser.
Patent•
18 Jan 1977
TL;DR: A variable orifice forming mechanism utilizing an iris shutter arrangement adapted to control gas flow, conductance in vacuum systems, as heat shield for furnace windows, as a beam shutter in sputtering operations, and in any other application requiring periodic or continuously variable control of material, gas, or fluid flow is described in this paper.
Abstract: A variable orifice forming mechanism utilizing an iris shutter arrangement adapted to control gas flow, conductance in vacuum systems, as a heat shield for furnace windows, as a beam shutter in sputtering operations, and in any other application requiring periodic or continuously-variable control of material, gas, or fluid flow.
Patent•
25 Nov 1977
TL;DR: In this paper, an improved Hartmann-type wavefront sensor with a modulated reference beam of light is presented. But the use of a modulating reference beam eliminates the necessity for precise optical alignment, which is difficult or impossible to maintain in most operating environments.
Abstract: An improved apparatus for sensing wavefront distortions in a return beam of light, such as a beam returned through a turbulent atmosphere or through an imperfect optical system from a radiating or illuminated object is disclosed. This apparatus includes the components typically present in a Hartmann-type wavefront sensor, and additionally includes means to provide a modulated reference beam of light which is combined with the return beam. The use of a modulated reference beam eliminates the necessity for precise optical alignment, which is difficult or impossible to maintain in most operating environments.
Journal Article•
TL;DR: In this article, the authors evaluate shear connector capacity and beam flexural capacity and compare such capacity and behavior with existing design criteria, and show that a composite beam with formed steel deck can be more accurately and conservatively estimated if the slab force is considered to act at the mid-depth of the solid portion of the slab above the ribs, rather than at the centroid of the concrete stress block.
Abstract: The results are presented of 17 full-scale tests of composite beams incorporating formed steel decks. The results were analyzed in conjunction with 58 additional tests conducted by other investigators. This report evaluates shear connector capacity and beam flexural capacity and behavior, and compares such capacity and behavior with existing design criteria. The flexural capacity of a composite beam with formed steel deck can be more accurately and conservatively estimated if the slab force is considered to act at the mid-depth of the solid portion of the slab above the ribs, rather than at the centroid of the concrete stress block. The following empirical expessions are presented: to determine the capcity of stud shear connectors in the ribs of composite beams with formed steel deck; the estimation of the deflection of a composite beam with partial shear connection with or without formed steel deck; and the estimation of the stress in the bottom steel fiber of a composite beam with partial shear connection with or without formed steel deck.
TL;DR: It is shown that by offsetting the fan beam detector from its symmetrical position by a fraction of the element spacing, and by making measurements over 360, the spatial resolution of the detector may be increased by up to a factor of two.
Abstract: Data collection for computed tomography (CT), using a fan beam of radiation, is considered in detail. The manner in which the required projection data set is built up as scanning proceeds is demonstrated. It is shown that by offsetting the fan beam detector from its symmetrical position by a fraction of the element spacing, and by making measurements over 360 degrees, the spatial resolution of the detector may be increased by up to a factor of two. Results of simulations relating to an actual CT device under construction are presented.
TL;DR: A criterion for optimal external beam radiation therapy and a method for generating the associated optimal dose distributions are presented and several optimal treatment plans illustrating its application are given.
Abstract: A criterion for optimal external beam radiation therapy and a method for generating the associated optimal dose distributions are presented. The optimal beam configuration is defined to be the one with a dose distribution which provides the best “least-squares fit” to the prescribed tumor contour, subject to constraints on the dose at nearby vulnerable sites. A FORTRAN program for the solution of this optimization problem has been constructed and several optimal treatment plans illustrating its application are given. In this program, a maximum of 72 coplanar beams may be accommodated with up to 4 different field sizes directed at a common axis from 18 different directions.
Patent•
22 Sep 1977
TL;DR: In this paper, the use of the diffraction element as the beam splitter allowed a wide area of the scanning beam to be split by a relatively thin member of a diffraction grating.
Abstract: In a device wherein a scanning beam from a light source is deflected by a light deflector, especially a rotatable polygonal mirror or a vibratory mirror and focused by an optical element such as a lens or the like to optically scan a surface to be scanned, thereby effecting writing and display of information, a synchronizing signal generator includes an optical system for taking out part of the scanning beam as a synchronizing beam for providing synchronism of signals in scanning In this device, a diffraction element such as a diffraction grating or the like serving as a beam splitter for splitting the deflected beam to obtain the synchronizing beam is disposed within the deviation range of the deflected beam, and the diffracted beam exiting from the diffraction element is directed to a photodetector so as to provide a synchronizing signal In this device, the use of the diffraction element as the beam splitter permits a wide area of the scanning beam to be split by a relatively thin member
Patent•
28 Dec 1977
TL;DR: An optical multiplexer-demultiplexer consisting of a light-focusing transmission body having a radially graded refractive index distribution and a reflection or transmission type diffraction grating was proposed in this article.
Abstract: An optical multiplexer-demultiplexer consisting essentially of a light-focusing transmission body having a radially graded refractive index distribution and a reflection or transmission type diffraction grating. The transmission body is given an axial length approximately equal to an integral multiple of one quarter of the pitch of undulation of an off-axis input light beam as travelling through the transmission body while the diffraction grating is arranged on the axis of the transmission body at a distance approximately equal to an odd multiple of one quarter of the pitch of beam undulation from one end face of the transmission body which is normal to the axis. A composite light beam directed into the transmission body is dispersed by the diffraction grating into wavelength components, which are separately focused to be extracted as through respective optical fibers. The device needs no separate optical elements such as reflecting mirrors or an independent diffraction grating and is not only particularly compact in size and stable on account of its integral structure but is capable of a high degree of multiplexing.
TL;DR: In this paper, a pulse-echo ultrasonic transducer probe includes a substantially centrally disposed axial bore running therethrough and a radial slot extending from the bore to the periphery of its housing.
Abstract: A pulse-echo ultrasonic transducer probe includes a substantially centrally disposed axial bore running therethrough and a radial slot extending from the bore to the periphery of its housing. A slotted cap dimensioned to rotatably fit over the top of the housing is provided with a hollow semi-circular stem extending into the bore, the slot of the cap being aligned with the longitudinal opening of the stem. The slot of the cap and that of the transducer, when passing a surgical instrument through the bore into an opaque body, are rotatably adjusted so that they are out of registry with one another for supporting the surgical instrument and for maintaining the instrument in the center of an ultrasonic search beam. Subsequently, after the instrument has reached the desired position in the body the slots are brought into registry for providing removal of the transducer probe from around the instrument.
TL;DR: The nonlinear optical coefficients of AlN have been determined as "d33" = (23.2±35%) dQ11 and "d31" ≲ 0.04"d33 for the c‐plate film and for a fundamental beam at 1.064 μm as discussed by the authors.
Abstract: The nonlinear optical coefficients of AlN have been determined as ‖d33‖= (23.2±35%) dQ11 and ‖d31‖ ≲0.04‖d33‖ for the c‐plate film and for a fundamental beam at 1.064 μm. The result is discussed with reference to the bond‐charge model.
TL;DR: In this paper, a technique for measuring material damping in specimens under forced flexural vibration was described, which can be used for testing fiber-reinforced composite materials, and it could be applied to any structural material.
Abstract: This article describes a technique for measuring material damping in specimens under forced flexural vibration. Although the method was developed for testing fiber-reinforced composite materials, it could be used for any structural material.
TL;DR: In this article, the difference between the pp total cross-sections for parallel and anti-parallel longitudinal spin states at beam momenta of 3 and 6 GeV/c was measured.
TL;DR: In this article, an energetic electron beam is injected into a cold, dense, almost collisionless magnetoplasma, and a lab experiment on a beam-plasma instability under conditions for which the theory of VLF hiss is applicable.
Abstract: The paper describes a lab experiment on a beam-plasma instability under conditions for which the theory of VLF hiss is applicable. An energetic electron beam is injected into a cold, dense, almost collisionless magnetoplasma. Beam and plasma dimensions are so large that oblique whistler wave propagation and growth are readily observable. The observations of frequency and wave number spectra, growth rate, and instability level are consistent with theory and satellite observation in regions of electron precipitation.
TL;DR: In this paper, a modified Lorentz function of the form A[1 + C(Δ2θ)2]−1.5 fitted over a range of two halfwidths on each side of the Bragg peak position was applied to profile refinement of data for rhombohedral La0.75Sr0.25CrO3, a perovskite-type compound which is slightly distorted from the ideal cubic structure.
Abstract: Data have been collected from a standard silicon sample with Cu Kβ radiation selected by means of a pyrolytic graphite monochromator mounted in the scattered beam. The peak shapes can be described reasonably well by Lorentz-type functions, but not by a Gaussian function. These results have been applied to the profile refinement of data for rhombohedral La0.75Sr0.25CrO3, a perovskite-type compound which is slightly distorted from the ideal cubic structure. The analysis, which employs a slightly modified version of a neutron profile program [Rietveld (1969), J. Appl. Cryst. 2, 65–71] indicates that the best compromise for the peak shape is a modified Lorentz function of the form A[1 + C(Δ2θ)2]−1.5 fitted over a range of two halfwidths on each side of the Bragg peak position. The results are compared with a similar refinement of neutron data collected from the same sample.