Small Beam Size Research Articles

High pressure experiments with synchrotron radiation

Using a diamond anvil cell (DAC), high pressure 57Fe Mossbauer spectroscopy has been performed with the nuclear forward scattering of synchrotron radiation. We used monochromatized synchrotron radiation from an in‐vacuum type undulator as a high‐density strong Mossbauer source with a quite small beam size. Pressure‐induced magnetic hyperfine interactions at 57Fe in SrFeO2.97 has been detected at 74 GPa by a quantum‐beat modulation of the decay rate after collective nuclear excitation with the synchrotron radiation pulse. Evidence for a transition from antiferromagnetism to ferromagnetism of Fe in SrFeO2.97 at 74 GPa and 300 K has been obtained from the nuclear forward scattering under a transverse magnetic field.

Extremely Small Beam Size Measurement by Laser Interferometer

Extremely Small Beam Size Measurement by Laser Interferometer

Use of the nuclear microprobe at the University of Arizona for the study of heavy metal deposition in rabbit renal tissue

Industrial wastes consigned to disposal sites frequently contain substantial amounts of heavy metals. We have successfully applied proton induced X-ray emission analysis (PIXE) in the conduct of heavy metal (Hg, Cd, Cr, As) toxicity studies using precision cut rabbit renal cortical slices. The large beam diameter (4000 μm) of the proton macroprobe at The University of Arizona Ion Beam Analysis facility allowed an overall concentration of the metal(s) of interest in the samples to be determined, but lacked the ability to resolve point concentrations in the tissue. The ability to locate these areas has now been made available to us with the addition of a rastering microprobe (μ-PIXE) to the facility. Studies now being conducted in our laboratory using this micro-technique include analysis of renal tissue taken from rabbits injected intraperitoneally with HgCl 2, K 2Cr 2O 7, and NaAsO 2. The small beam size (3 μm) and the ability to raster this beam over areas of up to 125 μm × 125 μm has allowed regional mapping of endogenous and non-endogenous metal concentrations and revealed trends in heavy metal deposition in in vivo treated renal tissue, significantly increasing the amount of information obtained from these animal studies using PIXE alone. The combination of small beam size, high resolution, and multi-element detection makes μ-PIXE a powerful tool for investigating the impact of non-endogenous metals on the kidney.

Cosmological-parameter determination with microwave background maps.

The angular power spectrum of the cosmic microwave background (CMB) contains information on virtually all cosmological parameters of interest, including the geometry of the Universe ($\ensuremath{\Omega}$), the baryon density, the Hubble constant ($h$), the cosmological constant ($\ensuremath{\Lambda}$), the number of light neutrinos, the ionization history, and the amplitudes and spectral indices of the primordial scalar and tensor perturbation spectra. We review the imprint of each parameter on the CMB. Assuming only that the primordial perturbations were adiabatic, we use a covariance-matrix approach to estimate the precision with which these parameters can be determined by a CMB temperature map as a function of the fraction of sky mapped, the level of pixel noise, and the angular resolution. For example, with no prior information about any of the cosmological parameters, a full-sky CMB map with 0.5\ifmmode^\circ\else\textdegree\fi{} angular resolution and a noise level of 15 \ensuremath{\mu}K per pixel can determine $\ensuremath{\Omega}$, $h$, and $\ensuremath{\Lambda}$ with standard errors of \ifmmode\pm\else\textpm\fi{}0.1 or better, and provide determinations of other parameters which are inaccessible with traditional observations. Smaller beam sizes or prior information on some of the other parameters from other observations improves the sensitivity. The dependence on the underlying cosmological model is discussed.

The Gas Field Ion Source for Finely Focused Ion Beam Systems

AbstractThe Gas Field Ion Source, GFIS, promises a 109A/(cm2 str) brightness, small beam sizes, and inert gas ion species. If this performance could be demonstrated on a commercial system, the GFIS might replace the liquid metal ion source as the standard source for FIB applications. Recent work at the Max-Planck-Institut für Kernphysik (MPI-K) in Heidelberg, Germany has shown that a GFIS with a ‘Super Tipped’ emitter can be reliably fabricated and can be run with stable helium beam current for more than 200 hours. However, this GFIS source must operate in a bakable UHV chamber, at cryogenic temperatures, and at high voltages with low vibration. A GFIS is now being integrated with high resolution ion optics and a vacuum chamber designed for studying GFIS image quality and ion induced chemistry.

Evaluation of correction factors for transmittance measurements in single-beam integrating spheres

An integrating sphere for transmittance measurements at normal and oblique angles of incidence has been constructed. The sphere is a single-beam instrument that uses a small-area silicon diode as the detector. The entry port is only 0.37% of the total wall area and has an oblong shape to permit measurements at high angles of incidence for scattering samples. A small beam size has been made possible by using a low-noise preamplifier system for the detector circuit. The oblong port shape and a small beam size make it possible to perform simulated double-beam measurements at near-normal incidence. Modified correction factors for the sample reflectance have been derived. Special attention has been paid to the separation into a diffuse and a specular component of the transmitted light. Results have been compared with the results of measurements on a double-beam instrument, and the correction factors for specular and diffuse samples have been experimentally verified. The importance of using the right correctionfactors for different types of samples has been evaluated together with the influence of the sphere parameters.

Behaviour of femtosecond pulses on the optical axis of a lens. Analytical description

The propagation of a femtosecond pulse along the optical axis of a lens is analytically described near the focus assuming homogeneous illumination. The results are compared with previous numerical calculations. The time dependence of the intensity in the focal point is also obtained. For small input beam size the diffraction, for large input beam size the pulse broadening causes the decrease of the intensity in the focal point. There is an optical input beam radius for the highest intensity and an analytical expression is derived for it.

球面ミラーと線状レーザ光を用いた空間座標位置の測定

A coordinate measurement method is developed which is based on optical triangulation and uses a spherical mirror as a target. Each of the three axes employs a slit-ray laser scanner and a photo-detector to detect the direction of the regular reflection from the target mirror. Since this method detects only the center of curvature of the mirror, it is suitable when the attitude of the target changes, e.g. a robot arm. Moreover, the use of the spherical mirror allows precise calibration and easy set up. To demonstrate this measurement method, coordinate values in one-dimension were measured at various distances. In this paper, the results form this one dimensional test are presented. The proposed measurement method was shown to be feasible through this experiment. The small beam size and small divergent angle of the light source produced high accuracy, while the detector size was found to have little effect on the accuracy. The measuring accuracy of the system was evaluated to be 20 μm at a distance of 750 mm.

Some application of synchrotron radiation

Continuous tuneable wavelength in the range 0.01A<λ<100A, high brilliance and parallelity of the beam are the outstanding properties for all applications of synchrotron radiation in condensed matter research. High angular and time resolution in synchrotron X-ray diffraction may be achieved. Powder Diffraction pattern with a full width at half maximum (FWHM) of Bragg reflections of ΔΘ-o.02 display a resolution about five times better than laboratory equipment. Thus the investigation of structural phase transitions with only minor metric changes are feasible as well as direct determination of crystal structures from powder data. Registration of complete powder patterns in a few milliseconds opens the road to kinetic studies of crystallisation from glasses or melt and to structural phase transitions. The information from diffraction experiments which provide information on long range order is related to X-ray absorption experiments (XANES and EXAFS). X-ray absorption will provide information on the local environment of atoms (EXAFS) or on its electronic nature. Texture, strain and stress investigations with synchrotron radiation offer advantages as compared to laboratory X-ray work. The angular resolution is considerably improved due to the parallel beam geometry and the small beam size and the penetration depth may be varied by a factor of 6. Thus not only general orientation distribution functions but the anisotropy strain and complex stress behaviour at surfaces may be investigated in particular grains. Furthermore all kinds of surface studies at grazing incidence are performed with considerable advantage

Three-dimensional free electron laser dispersion relation including betatron oscillations

Abstract We have developed a 3-D FEL theory based upon the Maxwell-Vlasov equations including the effects of the energy spread and emittance of the electron beam, and of betatron oscillations. The radiation field is expressed in terms of Green's function of the inhomogeneous wave equation and the distribution function of the electron beam. The distribution function is expanded in terms of a set of orthogonal functions determined by the unperturbed particle distribution. The coupled Maxwell-Vlasov equations are then reduced to a matrix equation, from which a dispersion relation for the eigenvalues is derived. In the limit of small betatron oscillation frequency, the present dispersion relation reduces to the well-known cubic equation of the one-dimensional theory in the limit of large beam size, and it gives the correct gain in the limit of small beam size. Comparisons of our numerical results with other approaches show good agreement. We present a handy empirical formula for the FEL gain of a 3-D Gaussian beam, as a function of the scaled parameters, that can be used for a quick estimate of the gain.

Single-longitudinal-mode operation and second-harmonic generation of Nd:YVO_4 microchip lasers

A single-mode output of 221 and 16 mW for the fundamental and second-harmonic light was obtained with the combination of a Nd:YVO(4) microchip laser and an intracavity KTP crystal. It was found that the beam size and laser power in a plano-plano cavity were dependent on the absorption coefficient of the laser medium and that the material that had a higher absorption coefficient produced higher output power and smaller beam size in the laser cavity. This means that Nd:YVO(4) is suitable not only for single-mode oscillation but also for efficient intracavity second-harmonic generation.

A method using an on‐line digital computer for the improvement of resolution of backscattered electron images

SUMMARYIn principle, the resolution of backscattered electron (BSE) images can be little improved, even though an infinitely small beam size is achieved by various improvements in the intrinsic instrument. In order to circumvent this problem, a method is proposed which utilizes an on‐line digital computer for the image recording and processing. The major image‐processing tools are reduction, expansion, super‐imposition with matching of the images, and high‐emphasis filtering in the Fourier domain. By using various combinations of these techniques, the resolution of BSE images has been significantly improved. The validity of these improved images has been confirmed. In the case of a BSE image with too wide a dynamic range, both the present method and digital homomorphic filtering provide successful results.

An experimental apparatus for measuring surface resistance in the submillimeter-wavelength region

A simple comparative technique to characterize surface electrical resistance of small metallic samples at submillimeter wavelengths is presented. A quasioptical hemispherical resonator, fed by an optically pumped far-infrared laser is used, with the sample serving as the plane mirror. The cavity developed combines a small beam size at the sample, enabling measurements on samples with widths as small as 5 mm, with a large quality factor Q, so that surface resistance losses are readily measurable. This cavity uses a simple new geometry that feeds the cavity through a single small coupling hole that also serves as a system of monitoring energy storage in the cavity by means of a single external beamsplitter. An alternate approach of inserting an internal beamsplitter into the resonator was found to be unacceptable due to excessive losses and alignment problems.

Absorbed dose to organs in the head and neck from bitewing radiography.

Dose measurements were carried out to estimate the absorbed dose to organs at risk from bitewing radiography under exposure conditions similar to those found in general dental practice in The Netherlands. The measurements were carried out in the head and neck of a Rando phantom using TLD-100 ribbons. Three different X-ray machines were used simulating 10 different exposure conditions to determine the effects of beam energy, beam size and focus-skin distance on the absorbed dose. The absorbed dose in the primary beam, close to the focal spot, decreased as the beam energy increased, while behind the film plane it increased with the beam energy. Outside the primary beam, at short distances from the skin surface, the absorbed dose decreased as the energy increased, while behind the film plane and at greater distances from the primary beam the absorbed dose increased as the beam energy increased. The absorbed dose was significantly lower for smaller beam sizes and for larger focus-skin distances, independent of beam energy.

A dispersion-free trajectory correction technique for linear colliders

In this paper, we describe a new trajectory correction technique for high energy linear accelerators. Current correction techniques force the beam trajectory to follow misalignments of the beam position monitors (BPMs). Since the particle bunch has a finite energy spread and particles with different energies are deflected differently, this causes “chromatic” dilution of the transverse beam emittance. The algorithm which we describe in this paper reduces the chromatic dilution by minimizing the energy dependence of the trajectory. To test the method we compare the effectiveness of our algorithm with a standard correction technique in simulations of the Stanford Linear Collider (SLC) linear accelerator and a design linac for a Next Linear Collider (NLC). While the simulations do not indicate that chromatic dilutions are a serious problem in the SLC linac, they would be debilitating in a future linear collider because of the very small beam sizes required to achieve the necessary luminosity. For example, in simulations of the NLC we have found that with typical alignment tolerances the beam size increased substantially after correcting the trajectory with a standard correction algorithm. In contrast, after correcting with our technique, the dilution was negligible. We feel that this technique will prove essential for future linear colliders.

A PIXE mini-beam setup at the bonn cyclotron for archeometric metal analyses

The exact analysis of the elemental composition at and around a soldering joint of an antique piece of jewelry can elucidate the joining technologies and give hints of the genuineness of the object. As analytical method we use PIXE, which is nondestructive, multielemental and with fundamental parameter calculations gives absolute concentration values. To obtain the necessary spot size of the H 2 + beam at the Bonn cyclotron we use a piezo-controlled diaphragm, whose demagnified image is focussed on the target by two magnetic quadrupole triplets. With an electrostatic deflector the beam spot of 0.1 × 0.3 mm 2 size can be moved 2 mm in each direction on the target. With a laser beam, which simulates the ion beam, an irregularly shaped archeological object can be positioned. The laser is also used to obtain the alignment of the target surface to the ion beam direction and the small beam size makes it easier to find a flat part on the surface of the object; both of these are important preconditions for using the fundamental parameter method. A scan over a joint of modern gold alloys demonstrates the ability to detect soldering joints. The analysis of four pieces of Roman gold jewelry found in the area of Cologne and Bonn shows examples of brazing with a solder as well as diffusion soldering.

Scanning reflection electron imaging of crystal surfaces

Scanning reflection electron imaging has been developed in recent years as a potential surface probing technique. The small beam size (0.5 nm) used in the SREM work make it possible to perform nano-scale analysis of crystal surfaces. Microdiffraction RHEED patterns can be obtained to identify surface reaction products. The problems of reductions on metal oxide crystal surfaces, metal surface oxidation processes and metal-substrate interactions have been investigated by SREM technique. Surface channelling effect have also been studied in SREM mode by taking advantage of the small incident beam size. In principle SREM images are analogous to, due to the reciprocity theorem, the REM images. In practice, in order to get reasonable signal large objective apertures are generally used whereas small detector apertures have to be used to obtain adequate image contrast. The main contrast mechanism in SREM images of atomic steps and surface defects may be due to phase contrast since most of the diffraction contrast will be washed out because of the large beam convergence. For example the RHEED pattern in figure 1 is effectively a convergent beam pattern and was obtained from a cleaved MgO (001) surface. These patterns are useful for determining the crystal orientation and for the inspection of diffraction conditions such as surface resonance condition. By employing small detector apertures and moderate objective apertures single atomic steps can be imaged with high contrast as shown in figure 2 which is a SREM image of platinum (111) surface obtained with (555) specular beam excited. The characteristic black and white contrast of the down and up steps is revealed clearly (arrowed in fig. 2). The similarity between the SREM image and the corresponding REM images suggests that the two imaging modes are equivalent.

Emittance studies at the Los Alamos national laboratory free electron laser

Recent emittance studies at the Los Alamos FEL have indicated several areas of concern in the linac and beamline feeding the wiggler. These studies included both experimental measurements and computer simulations. The beamline starts with a 5 A micropulse from the thermionic cathode in the gun. After bunching by velocity modulation and acceleration to 20 MeV in a 1300 MHz standing wave accelerator, the beam current is roughly 250 A. Final bunching to 800 A is performed in the nonisochronous bend that rotates the electrons onto the axis of the wiggler and the optical cavity.Four emittance growth mechanisms of special importance have been studied. First, a rapid growth of the electron beam's emittance immediately after the spherical gridded Pierce gun resulted, in part, from the long time required for our pulsing electronics to ramp the grid voltage up at the start and down at the end of the pulse, which created a pulse with a cosine-like current distribution as a function of time. The growth was compounded by the extremely small radial beam size (almost a waist) leaving the gun. In addition, we saw evidence of electrostatic charging of the insulators in the gun, reducing the quality of the electron beam further. Second the action of the solenoidal focusing fields in the low-voltage bunching region was studied, and criteria for a minimum emittance growth were established. Third, maximum misalignment angles and displacements for various elements of the beamline were calculated for the desired low emittance growth. Finally, emittance growth in the horizontal dimensions through the nonisochronous bend caused by varying energy depression on the particles due to longitudinal wake fields was both calculated and observed. In addition, we measured energy depressions caused by the wake fields generated by various other elements in the beamline. Strategies were developed to relieve the magnitude of these wake-field effects.

First operation of an extended range grasshopper monochromator on the Aladdin storage ring

First operation of a new extended range monochromator on the 1 GeV storage ring Aladdin is described. Curves are given of output flux as a function of photon energy for the 2 m and for the 5 m gratings as measured with an NBS diode. Relatively low background and flux up to 1500 eV is obtained using a 1200 line/mm 5 m holographic grating. Highly reproducible scans were obtained of the transmission of thin films including the carbon K and titanium L edges. This reproducibility and high throughput is in large part due to the small beam size and excellent stability of Aladdin.

JHKL PHOTOMETRY OF THE NUCLEI OF NORMAL SPIRAL GALAXIES.

ABSTRACT Photometry with a small beam size is presented of the nuclei of five spiral galaxies selected for the absence of nuclear activity. No infrared excesses are found, and the color indices of all five galaxies are the same within the uncertainties. The emission of this sample can be explained in terms of a late-type stellar population. These results contrast with earlier results both for Seyfert nuclei and some supposedly normal spiral nuclei, which showed 3.5-μm excesses.