High-resolution Beam Research Articles

On the Electric Dipole Moments of Asymmetric Tops: Measurement by High-Resolution Electronic Spectroscopy in the Gas Phase

Reported here are Stark-effect measurements of the permanent electric dipole moments of two structural isomers of aminobenzonitrile, 2ABN and 3ABN, using high-resolution laser molecular beam techniques. When combined with previous results on 4ABN, the data show that each structural isomer has a unique dipole moment, in both its ground (S(0)) and electronically excited (S(1)) states, thereby providing a means of distinguishing them. Possible applications of the method to other, biologically relevant molecules are discussed.

Photoacoustic technique to measure beam profile of pulsed laser systems.

The beam profiles of pulsed lasers are currently measured using either complementary metal oxide semiconductor (CMOS) or charge coupled device (CCD) cameras. Despite providing high-resolution beam profiles, these devices cannot work with high power lasers. If additional optical attenuators are used, beam distortions may occur. In this paper we demonstrate a high-resolution photoacoustic technique capable of measuring the beam profile of pulsed lasers. The beam profiles of a pulsed neodymium-doped yttrium aluminium garnet (Nd:YAG) laser and a pulsed optical parametric oscillator (OPO) laser system were measured using a polydimethylsiloxane film and a single element high-frequency ultrasonic transducer. The advantages and limitations of the developed photoacoustic technique are discussed.

Measurement of high energy resolution inelastic proton scattering at and close to zero degrees

Measurements of inelastic proton scattering with high energy resolution at forward scattering angles including 0 ∘ are described. High-resolution halo-free beams were accelerated by the cyclotron complex at the Research Center for Nuclear Physics. Instrumental background events were minimized using the high-quality beam. The remaining instrumental background events were eliminated by applying a background subtraction method. As a result, clean spectra were obtained even for a heavy target nucleus such as Pb 208 . A high energy resolution of 20 keV (FWHM) and a scattering angle resolution of ± 0 . 6 ∘ were achieved at an incident proton energy of 295 MeV.

Fabrication and Formation Mechanism of Flowerlike Bicephalous TiB<sub>2</sub> Nanowhisker Clusters

Flowerlike bicephalous titanium diboride (TiB2) nanowhisker clusters were fabricated by planetary ball-milling. The pure cleavage theory and crack growth mechanism were used to explain the formation process. The high-resolution transmission electron microscopy and nano electronic beam diffraction show that TiB2 superhard material always has a cleavage plane along the direction of [0001] zone axe and [10 0] zone axe because of its big interplane distance, weak bonding force between planes and low index directions. The flowerlike bicephalous TiB2 nanowhisker can be gained after repeated cleavage under high strains. The discovery could open a new path to fabricate C32 type superhard ceramic nanowhiskers.

Evaluation of high-resolution cone beam computed tomography in the detection of simulated interradicular bone lesions

The purpose of this study is to assess the accuracy of limited-volume high-resolution cone beam CT (CBCT) in the detection of periodontal bone loss. 163 simulated periodontal lesions of different depths were created in dried human hemimandibles. Specimens were imaged using the intraoral paralleling technique and limited-volume CBCT (3DX Accuitomo; Morita Co. Ltd, Kyoto, Japan). Ten viewers examined the images. Data were analysed with receiver operating characteristics (ROC) analysis. ROC curves were generated and the areas under the maximum-likelihood curves (A(z)) were compared. Other statistical analyses were used to detect the normality of the distribution of the results. The results are reported as the individual viewer ROC curve areas for each of the two imaging modalities. In all experiments the A(z) area for CBCT (0.770-0.864) was larger than the A(z) area for periapical film (0.678-0.783); statistical tests showed a statistically significant difference between the two modalities. Results indicate that the CBCT technique has better accuracy and diagnostic value than periapical films in the detection of interradicular periodontal bone defects.

Performance of a reentrant cavity beam position monitor

The beam-based alignment and feedback systems, essential operations for the future colliders, require high resolution beam position monitors (BPMs). In the framework of the European CARE/SRF program, a reentrant cavity BPM with its associated electronics was developed by the CEA/DSM/Irfu in collaboration with DESY. The design, the fabrication, and the beam test of this monitor are detailed within this paper. This BPM is designed to be inserted in a cryomodule, work at cryogenic temperature in a clean environment. It has achieved a resolution better than $10\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ and has the possibility to perform bunch to bunch measurements for the x-ray free electron laser (X-FEL) and the International Linear Collider (ILC). Its other features are a small size of the rf cavity, a large aperture (78 mm), and an excellent linearity. A first prototype of a reentrant cavity BPM was installed in the free electron laser in Hamburg (FLASH), at Deutsches Elektronen-Synchrotron (DESY) and demonstrated its operation at cryogenic temperature inside a cryomodule. The second, installed, also, in the FLASH linac to be tested with beam, measured a resolution of approximately $4\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ over a dynamic range $\ifmmode\pm\else\textpm\fi{}5\text{ }\text{ }\mathrm{mm}$ in single bunch.

Efficient multiple beam ion optics for quantitative surface analysis: from simulations to a fully operational instrument

A new ion optics system was developed and experimentally tested, which allows for high-resolution multiple beam characterization of materials. This system enables: (1) efficient, quasi-simultaneous measurements of the mass spectra of laser post-ionized sputtered species and secondary ions as well as secondary electron imaging, that can be accompanied and assisted by (2) low energy ion milling and (3) in-situ optical imaging and laser desorption with submicron resolution. Altogether, this ion optics system provides a versatile, sensitive combination of an analytical mass spectrometer and ion, electron and optical microscopes, which can efficiently detect one out of four sample atoms consumed during the analysis.

High resolution beam line for the SHARAQ spectrometer

The high resolution beam line for the SHARAQ spectrometer was designed to satisfy the lateral and angular dispersion matching conditions based on the precise ion optical calculation using the measured magnetic field maps of the beam line magnets. The higher order aberration due to the large emittance of the secondary RI-beams was corrected by employing the three octupole magnets. A Monte Carlo calculation was carried out to examine the beam profile on the SHARAQ target, and it was found that the octupole magnets actually correct the higher order aberration.

High-resolution angular beam stability monitoring at a nanofocusing beamline

Two semi-transparent imaging beam-position monitors developed at the ESRF have been installed at the micro-analysis beamline ID22 for monitoring the angular stability of the X-ray beam. This system allows low-frequency (10 Hz) angular beam stability measurements at a submicroradian range. It is demonstrated that the incoming macro-beam angular fluctuations are one of the major sources of focal spot instabilities downstream of the Kirkpatrick-Baez mirrors. It is also shown that scanning the energy by rotating the so-called fixed-exit monochromator induces some unexpected angular beam shifts that are, to a large extent, deterministic.

Cavity BPM system tests for the ILC energy spectrometer

The main physics programme of the International Linear Collider (ILC) requires a measurement of the beam energy at the interaction point with an accuracy of 10-4 or better. To achieve this goal a magnetic spectrometer using high resolution beam position monitors (BPMs) has been proposed. This paper reports on the cavity BPM system that was deployed to test this proposal. We demonstrate sub-micron resolution and micron level stability over 20h for a 1m long BPM triplet. We find micron-level stability over 1h for 3 BPM stations distributed over a 30m long baseline. The understanding of the behaviour and response of the BPMs gained from this work has allowed full spectrometer tests to be carried out.

Frequency-swept directivity lobes—An emerging functional principle of biosonar beamforming

In all bat species, the spatial sensitivity of the biosonar system is mainly determined by the shape of the outer ears. In addition, a noseleaf surrounds the nostrils in many species and shapes the spatial distribution of the emitted sound energy. Predicting the beam-forming effects of these structures numerically from their surface geometry has enabled comparative studies of high-resolution beam pattern estimates across a large set of different bat species. The beam patterns obtained so far differ from common manmade transducers, such as loudspeakers and microphones. Strong asymmetric side lobes, which change direction as a function of frequency, are a distinguishing feature consistently seen in emission and reception beam patterns of the bats. Where investigated, the occurrence of these side lobes appears to be tied to the presence of flap-like structures (including the tragus of the pinna), which may be hypothesized to have evolved for this purpose. The presence of these side lobes suggests that bat biosonar has not been evolved to maximize the ensonification energy and sensitivity for a single small target unconditionally. Instead, the function of these strong side lobes could be explained as maximizing the information obtained in analogy to squinted beams used in manmade systems.

High precision SC cavity alignment measurements with higher order modes

Experiments at the FLASH linac at DESY have demonstrated that the higher order modes (HOMs) induced in superconducting cavities can be used to provide a variety of beam and cavity diagnostics. The centres of the cavities can be determined from the beam orbit which produces minimum power in the dipole HOM modes. The phase and amplitude of the dipole modes can be used as a high resolution beam position monitor. For most superconducting accelerators, the existing HOM couplers provide the necessary signals, and the downmix and digitizing electronics are straightforward, similar to those for a conventional BPM.

Monoenergetic source of kilodalton ions from Taylor cones of ionic liquids

The ionic liquid ion sources (ILISs) recently introduced by Lozano and Martinez Sanchez [J. Colloid Interface Sci. 282, 415 (2005)], based on electrochemically etched tungsten tips as emitters for Taylor cones of ionic liquids (ILs), have been tested with ionic liquids [A+B−] of increasing molecular weight and viscosity. These ILs have electrical conductivities well below 1S∕m and were previously thought to be unsuitable to operate in the purely ionic regime because their Taylor cones produce mostly charged drops from conventional capillary tube sources. Strikingly, all the ILs tried on ILIS form charged beams composed exclusively of small ions and cluster ions A+(AB)n or B−(AB)n, with abundances generally peaking at n=1. Particularly interesting are the positive and negative ion beams produced from the room temperature molten salts 1-methyl-3-pentylimidazolium tris(pentafluoroethyl) trifluorophosphate (C5MI–(C2F5)3PF3) and 1-ethyl-3-methylimidazolium bis(pentafluoroethyl) sulfonylimide (EMI–(C2F5SO3)2N). We extend to these heavier species the previous conclusions from Lozano and Martinez Sanchez on the narrow energy distributions of the ion beams. In combination with suitable ILs, this source yields nanoamphere currents of positive and negative monoenergetic molecular ions with masses exceeding 2000amu. Potential applications are in biological secondary ion mass spectrometry, chemically assisted high-resolution ion beam etching, and electrical propulsion. Advantages of the ILISs versus similar liquid metal ion sources include the possibility to form negative as well as positive ion beams and a much wider range of ion compositions and molecular masses.

The Growth Characteristics of a GaN Layer on a Cone-Shaped Patterned Sapphire Substrate by TEM Observation

The growth characteristics of a GaN layer deposited on a cone-shaped patterned sapphire substrate (PSS) by using metalorganic chemical vapor deposition (MOVCD) were observed by transmission electron microscope (TEM) to investigate the influence of cone-shaped PSS on the GaN layer. The GaN/sapphire interfaces were analyzed by using high-resolution TEM (HRTEM) and convergent beam electron diffraction (CBED), and the residual strain was evaluated by measuring the variation of the lattice parameters quantitatively. From the TEM images, a large number of threading dislocations were found above the flat region of the GaN/sapphire interface. In contrast, only a few threading dislocations were identified above the cone-shaped region. The HOLZ pattern analysis revealed that the lattice parameter of the GaN layer was lower above the flat region of the GaN/sapphire interface compared with the cone-shaped region, and the difference was estimated to be about 0.1 %. This may be attributed to the formation of a GaN layer by the lateral overgrowth above the cone-shaped region, resulting in less lattice mismatch and incoherency between the GaN layer and the sapphire substrate.

Scanning Transmission X-Ray Microscopy of Curative and Filler Migration of Inner Liner Compounds

Abstract Materials of significance in the rubber industry generally consist of a complex blend of elastomers, fillers, curing agents and other additives. Elucidating the complex microstructure-to-property relationship of these materials is essential for optimal product development. This requires characterization techniques that are capable to differentiate, map, and quantify these similar materials with sufficiently high spatial resolution. A technique that can provide such chemical microspeciation is Scanning Transmission X-ray Microscopy (STXM). STXM is a beamline based microscopy that utilizes the chemical specificity of Near Edge X-ray Absorption Fine Structure (NEXAFS) combined with zone plate optics to achieve high spatial resolution (< 50 nm) and low beam damage to allow the successful characterization of multi-component materials that would be difficult or impossible with other techniques. A brief introduction to the technique will be presented along with example applications showing curative and filler distribution mapping in multi-component elastomeric systems.

High-resolution beam energy-spread measurements using combination of nuclear resonant reactions and a 0° beam line separation

The energy spread of a proton beam from a single-ended accelerator at TIARA in JAEA Takasaki was measured using nuclear reactions with narrow resonance widths in order to evaluate chromatic aberrations in a micorbeam or a nanobeam probe forming system. The experiment was carried out on a 0° beam line of the accelerator to measure the beam energy spread generated by the accelerator directly. A beam separation method using permanent magnets attached to the accelerating tube was developed in order to select the proton beam from molecular hydrogen beams in the 0° beam line. This method led us to improve the signal-to-noise ratio of the γ-ray detection. The average energy spread of proton beams from the accelerator was evaluated to reach 3.6 × 10 −4 at beam energies over 2 MeV using the method with a resolution of 2 × 10 −5. The combination of the nuclear reaction with narrow resonance width and the beam separation method was essential for the beam energy spread measurement with high resolution (on the order of 10 −5 ). The beam energy spread measurement method enables us to evaluate proton beams generated by the stabilized accelerator to produce nanobeams.

Ultra long high resolution beam by multi-zone rotationally symmetrical complex pupil filter

An ultra long high resolution beam with extension of depth of focus (DoF) in the axial direction as well as high resolution in the transverse direction has been demonstrated by a seven-zone rotationally symmetrical complex pupil filter imposed at the aperture of a focusing lens. Both amplitude and phase of the transmitted light are modulated in different zones. The scalar diffraction theory is used to optimize the zone parameters. Simulation results show that extended DoF of the beam is increased by 16 times while the spot size at the beam waist is reduced to 0.7 times.

Design and optimization of microlens array based high resolution beam steering system

High-resolution imaging and beam steering using 3 microlens arrays (MLA) is demonstrated. Small lateral displacement of one microlens array is sufficient for large angle beam steering. A prescan lens is added to the system to overcome the discrete addressing problem associated with microlens scanning systems. A hybrid method that uses both geometrical ray tracing optimization and physical optics simulation is introduced for the design and optimization of the MLA system. Feasibility of 1880 x 1880 resolution using f/2 aspherical MLAs and 752 x 752 resolution using f/5 spherical MLAs are demonstrated assuming 100 microm microlens pitch and 2mm clear aperture. The system is compact and suitable for endoscopic imaging and agile steering of large beams.

One route for low dimensional oxide design: understanding their complexity

The design of new architectures and the optimization of particular properties need detailed knowledge of the real crystalline state and structural mechanisms of the materials. In this feature article, we intend to illustrate how combination of two complementary techniques, high resolution electron microscopy (HREM) and beam diffraction techniques (electrons, X-rays, neutrons), is efficient. Three examples of low dimensional oxides are presented, focussing our attention on the existence of successive ‘structural’ levels.

High precision superconducting cavity diagnostics with higher order mode measurements

Experiments at the FLASH facility at DESY have demonstrated that the higher order modes induced in superconducting cavities can be used to provide a variety of beam and cavity diagnostics. The axes of the modes can be determined from the beam orbit that produces minimum power in the dipole HOM modes. The phase and amplitude of the dipole modes can be used to obtain high resolution beam position information, and the phase of the monopole modes to measure the beam phase relative to the accelerator rf. For most superconducting accelerators, the existing higher order mode couplers provide the necessary signals, and the downmix and digitizing electronics are straightforward, similar to those for a conventional beam position monitor.