正方形连续变电位四极透镜在宽带示波管中的应用

正方形连续变电位边界可以产生理想四极场。本文介绍了利用这种四极场构成的透镜在宽带示波管中的应用进展。透镜由真空蒸镀高阻膜制成,实验中它分别取代了示波管中金属电极四极透镜和栅网,进行单方向和X、Y两个方向的偏转放大,前者获得了较好的图形质量,而后者得到了较大的放大率。文中对尚存的热功耗问题进行了讨论。     

Uncertainty of Cesium-Beam Time Standards Due to Beam Asymmetry

As a consequence of the spatial phase distribution in the resonators of cesium-beam time and frequency standards, the generated frequency depends on the specific path of the atomic beam. A change of the position of the atomic beam source may result in a beam displacement normal to the beam direction. For a deflection system consisting of a combination of quadrupole and hexapole magnets for two-dimensional beam deflection, the displacement of the center of mass of the beam resulting from a misalignment of the beam source is computed. To this end, the distribution of the beam intensity on the collector is first determined. It is shown that for the cesium-beam time and frequency standard CSI of the Physikalisch-Technische Bundesanstalt (PIB), the uncertainty of the position of the center of mass of the beam entails a contribution to the uncertainty of the standard of less than 1 X 10-15. The amount of the displacement of the center of mass of the beam can be determined from the decrease of the beam flux on the collector caused by an adjustment of the beam source.     

Superconducting magnets for the CBA project

The superconducting magnets that were designed and tested for the BNL colliding beam accelerator are described, including dipoles, quadrupoles and trim coils. The dipoles had an effective length of 436 cm, a good field aperture of 8.8 cm diameter, and were designed for an operating field of 5.28 T in a temperature range between 2.6 K and 3.8 K (provided by supercritical helium). The quadrupoles had the same aperture, an effective length of 138.5 cm, and were designed to operate in series with the dipoles, with a gradient of 70.8 T/m. The dipoles incorporated internal sextupole, octupole, and decapole trim coil windings; the quadrupole trim coils consisted of dipole, quadrupole, and dodecapole windings. The design, construction, and performance (training, field quality, quench protection characteristics) of prototype magnets are discussed in considerable detail.     

Research on Cs Beam Frequency Standards at the PTB: Beam Optics, Majorana Transitions

Results on theoretical and experimental studies on Cs beam optics using quadrupole and hexapole magnets and a combination of both, are reported. The efficiency of the deflection system and the velocity distribution in the beam have been computed for extended beam sources and compared with experimental results. An appropriate combination of magnets yielded a strong beam with a narrow relative half-width velocity range of about 7 percent. Design problems of Cs standards are discussed. A new wedge-shaped analyzer flop-in magnet is under study. Frequency shifting effects due to Majorana transitions are reported and the frequency shifting mechanism is discussed.     

The Columbia University sub-micron charged particle beam

A lens system consisting of two electrostatic quadrupole triplets has been designed and constructed at the Radiological Research Accelerator Facility (RARAF) of Columbia University. The lens system has been used to focus 6 MeV ⁴He ions to a beam spot in air with a diameter of 0.8 μm. The quadrupole electrodes can withstand voltages high enough to focus ⁴He ions up to 10 MeV and protons up to 5 MeV. The quadrupole triplet design is novel in that alignment is made through precise construction and the relative strengths of the quadrupoles are accomplished by the lengths of the elements, so that the magnitudes of the voltages required for focusing are nearly identical. The insulating sections between electrodes have had ion implantation to improve the voltage stability of the lens. The lens design employs Russian symmetry for the quadrupole elements.     

Reconfigurable electro-optical waveguide for optical processing

A highly versatile electro-optically induced waveguide is proposed, and some of its applications are discussed. The In(1-s)Ga(s)As(t)P(1-t)-based device can reconfigure an arbitrary refractive-index profile with high speed by using an array of stripe electrodes deposited along the device. This device can act as a variable fractional Fourier transformer or as a beam shaper. Some nonguiding applications based on a specific refractive-index patterning that is normal to the light-propagation direction, such as phase modulation and beam steering, can also be implemented with this device.     

Improving the performance of a quadrupole time-of-flight instrument for macromolecular mass spectrometry

We modified and optimized a first generation quadrupole time-of-flight (Q-TOF) 1 to perform tandem mass spectrometry on macromolecular protein complexes. The modified instrument allows isolation and subsequent dissociation of high-mass protein complexes through collisions with argon molecules. The modifications of the Q-TOF 1 include the introduction of (1) a flow-restricting sleeve around the first hexapole ion bridge, (2) a low-frequency ion-selecting quadrupole, (3) a high-pressure hexapole collision cell, (4) high-transmission grids in the multicomponent ion lenses, and (5) a low repetition rate pusher. Using these modifications, we demonstrate the experimental isolation of ions up to 12 800 mass-to-charge units and detection of product ions up to 38 150 Da, enabling the investigation of the gas-phase stability, protein complex topology, and quaternary structure of protein complexes. Some of the data reveal a so-far unprecedented new mechanism in gas-phase dissociation of protein oligomers whereby a tetramer complex dissociates into two dimers. These data add to the current debate whether gas-phase structures of protein complexes do retain some of the structural features of the corresponding species in solution. The presented low-cost modifications on a Q-TOF 1 instrument are of interest to everyone working in the fields of macromolecular mass spectrometry and more generic structural biology.     

Spatial transformation of Laguerre–Gaussian laser modes

Abstract

A method is described to spatially transform the annular profile of an arbitrary high-order Laguerre-Gaussian (LG) laser mode into an ultranarrow annulus using a combination of an axicon and a lens. The method is shown to conserve the azimuthal phase variation of the illuminating LG mode. The thin annular (hollow) light beam generated possesses orbital angular momentum and is suitable for experimental studies with cold atoms.     

Hemispherical concentrators and spectral filters for planar sensors in diffuse radiation fields

A dielectric hemisphere of refractive index N can act as an N(2) concentrator of isotropic diffuse radiation under appropriate conditions. We give an analytic expression for the gain of a concentrator of arbitrary radius, neglecting surface reflections, and numerical methods for calculating the gain when the surface transmissivity is an arbitrary function of incidence angle. The theory is applied to the design of multilayer spectral filters for hemispherical concentrators. When an appropriate wavelength shift is incorporated into the design process, an 11-layer, coupled-cavity spectral filter on the surface of a hemisphere of index 1.5 shows excellent bandpass performance with a concentrator radius as small as 3 times the sensor radius. This concentrator-filter combination shows a peak response of 97% of the ideal N(2) response at 950 nm, together with a FWHM of 55 nm.     

Modification of an achromatic mass spectrometer to include transverse focusing

Modification has been made to a magnetic mass spectrometer, comprising a magnetic prism and a parallel plane mirror, to increase its transmission and to obtain a stigmatic image. This has been done by adding two quadrupole lenses, one between the magnetic prism and the mirror to add some focusing in the transverse direction, the other after the mirror to correct the astigmatism created by the first quadrupole lens. In this paper, we derive all the parameters of the quadrupole lenses needed to ensure this objective.     

Leading order hard edge fringe fields effects exact in (1 + δ) and consistent with Maxwell's equations for rectilinear magnets

In a circular machine, where the linear lattice functions (α, β, γ) and a phase advance can be defined, one expects the fringe field effects to be negligible if the change in these functions is small through the element. However, this may not always be the case. In such situations, it is useful to have a leading order result which is adapted to tracking and analytical analysis. In this paper, we provide such a result for the quadrupole and we also provide a general formula for the effect of an arbitrary rectilinear multipole.Starting from the standard multipole expansion for the B field of a 2(n + 1)-pole (n ≥ 1), we compute the missing terms in the vector potential expansion consistent with the pure 2(n + 1)-pole symmetry. We then compute the leading effects of the fringing fields of a multipole on the dynamics. Finally, we apply this result to quadrupoles and reproduce the original results of Lee-Whiting, Matsuda, and Wollnik.For the quadrupole, we show how to write a symplectic (canonical) integrator for the dynamics which can be used in a standard circular machine kick code. For higher order multipoles, we display the implicit characteristic function solution as first proposed by Dragt.     

Infrared multiphoton dissociation in an external ion reservoir.

In this work we present a novel scheme for performing infrared multiphoton dissociation (IRMPD) external to the mass analyzer in an external ion reservoir consisting of an rf-only multipole and a pair of electrostatic lens elements. Ions generated by electrospray ionization (ESI) are accumulated in an rf-only hexapole and dissociated by irradiation at 10.6 microns from a CW CO2 laser in the source region of the mass spectrometer. This scheme is unique from other IRMPD schemes as dissociation occurs in a spatially distinct region of the spectrometer and is independent of the mass spectrometry platform used to analyze the fragment ions. The effectiveness of the technique is demonstrated with ESI IRMPD FTICR mass spectrometry of a 20-mer phosphorothioate oligonucleotide. A comparison of the external IRMPD scheme with nozzle-skimmer dissociation and conventional in-cell IRMPD reveals a significant improvement in signal-to-noise ratio and fragment yield, particularly for larger, more highly charged fragment ions.     

Effects of a Small Inclination Misalignment in Talbot Interferometry by Use of Gratings with Arbitrary Line Orientation. II. Experimental Verification

The theoretical results of the effects of a small inclination misalignment, which is formed by rotation of the beam-splitter grating around the axis on the grating plane when the axis has an arbitrary angle with respect to the line direction of the grating, between the two grating planes on the moiré fringes in the Talbot interferometry are verified by experiment. The experimental results coincide well with theoretical ones. Consequently, the effect of the small arbitrary inclination on practical measurements based on the Talbot interferometry is further explained by an example that examines the beam collimation of a lens, and the advantages and limitations of the effect are also discussed.     

Electromagnetic quadrupole-octupole lens

A design is proposed for an electromagnetic quadrupole lens with correction for spherical chromatic aberration. This lens consists of eight electrodes, of which four are also the poles of the magnet. Pis’ma Zh. Tekh. Fiz. 25, 5–7 (November 12, 1999)     

Flow fractionation of microparticles under a dielectrophoretic field in a quadrupole electrode capillary.

A technique of fractionation for microparticles was proposed that utilized a unique combination of a dielectrophoretic (DEP) field generated by a quadrupole electrode and a laminar flow in a capillary of 82.5 microm in radius. The fabricated capillary possessed four platinum wires in its inside wall as a quadrupole electrode. In a nonuniform electric field generated by the quadrupole electrode, microparticles, such as polystyrene and carbon, in water experienced DEP forces in the radial direction. When a sample solution was pumped in, an ideal laminar flow perpendicular to the DEP force was formed inside the capillary. The microparticles dynamically migrated by the DEP force across the laminar flow while they were carried by the flow. A theoretical model taking the DEP force and the laminar flow pattern into account predicted the elution profiles of the single microparticles quantitatively. The elution times of the microparticles depended on the dielectric properties and the sizes of the microparticles, as well as the voltage and frequency of the applied alternating current.     

Holographic zone plates for f x theta and collimating lenses

A holographic zone plate generated by subtracting the spherical wave phase is proposed, that is, a hologram generated by using two divergent or convergent spherical waves. This holographic zone plate can correct the increase in focal power in a radial direction in contrast with the interferometric zone plate. Use of this holographic zone plate for f x O and collimating lenses is analyzed. For an f x O lens, it is shown that an optimum combination of recording spherical waves exists that satisfies both scan linearity and image field flatness. For a collimating lens for a laser diode, it is shown that aberration can be corrected for different playback wavelengths from that used during recording.     

Coherent and incoherent combination of Gaussian beams employing lens array distributed on the spherical chamber

Coherent and incoherent combination of Gaussian beams employing a lens array distributed on the spherical chamber is theoretically analyzed. The output field of each source in the array is coupled through an individual optical system whose local optical axis coincides with the radial direction of the chamber. The resulting intensity profile near the origin is derived. The intensity profile and power in the bucket on the target for rectangular and hexagonal arrangement are numerically calculated. The influences of the center-to-center separation and the ring number of the focusing lens array are given. The synthetic intensity profile of incoherent combination changes little for a lens array scale much smaller than the chamber size. In contrast, the synthetic intensity profile of coherent combination shows an interference pattern with a sharp central peak and sidelobes.     

A status report of the ISOL facility in Lanzhou

A new ISOL facility has been constructed for on-line use with the heavy-ion accelerator HIRFL in Lanzhou. The focal principle of ISOLDE-type separators is modified by including a quadrupole doublet lens in front of the magnet. The mass spectra of Ar and Xe isotopes were measured with a scanner inside the collection chamber in an off-line test. The resolving power is equal to 700–1200 by only using a single einzel lens.     

Improvement of anisotropy sensitivity in the scanning acoustic microscope

The response of the conventional scanning acoustic microscope (SAM) to anisotropic materials is theoretically investigated. For this purpose, the reflection coefficient of plane acoustic waves incident on a liquid-solid interface is numerically calculated for a general anisotropic solid oriented in any arbitrary direction. In general, the reflection coefficient depends on polar and azimuthal angles of incidence. For the case of a circularly symmetric acoustic microscope lens, a mean reflectance function can be defined that depends only on the polar angle. With this mean reflectance function, it is very easy to predict the anisotropic material response of the acoustic microscope. It is found that, under certain conditions, the amplitude response of the acoustic microscope can depend heavily on the orientation of the solid material under investigation. The amplitude of the acoustic microscope signal is influenced by the orientation of the material because there is a cancellation of acoustic rays reflected from the object surface at different azimuthal angles. This cancellation is revealed as a minimum in the mean reflectance function. It is shown by numerical simulation that the sensitivity to orientation can be increased by the use of a ring-shaped insonification at the back of the acoustic lens.