Characterization of an ultraviolet and a vacuum-ultraviolet irradiance meter with synchrotron radiation

We have constructed and characterized a simple probe that is suitable for accurate measurements of irradiance in the UV to the vacuum UV spectral range. The irradiance meter consists of a PtSi detector located behind a 5-mm-diameter aperture. The probe was characterized at various wavelengths ranging from 130 to 320 mm by use of continuously tunable synchrotron radiation from the Synchrotron Ultra-violet Radiation Facility III. We determined the irradiance responsivity by scanning a small monochromatic beam over the active area of the irradiance meter and measuring its response on a grid with regular spacing. The angular response was also determined and shown to be suitable for applications such as photolithography. In addition, we studied the radiation damage using a 157-nm excimer laser and found that the irradiance meter can endure more than 100 J/cm2 of 157-nm radiation before a noticeable change occurs in its responsivity. Many industrial applications such as UV curing, photolithography, or semiconductor chip fabrication that require accurate measurement of the irradiance would benefit from having such a stable, accurate LTV irradiance meter.     

SU5: a calibrated variable-polarization synchrotron radiation beam line in the vacuum-ultraviolet range

SU5 is a high-resolution variable-polarization synchrotron radiation (SR) beam line with which linear and circular dichroism experiments are performed in the vacuum ultraviolet (VUV) range (5-40eV), based on an electromagnetic crossed undulator called the Onduleur Plan/Helicoidal du Lure à Induction Electromagnétique (OPHELIE). To get precise knowledge of the polarization state of the emitted SR and to take into account the polarization transformations induced by reflection on the various optics, we set up an in situ VUV polarimeter to provide a precise and complete polarization analysis of the SR atthe sample location. The overall measured polarization performances were highly satisfactory, with measured linear polarization rates of more than 98% (83%) in the vertical (horizontal) linear polarization mode and an average 92.1% (95.2%) circular polarization rate for the right- (left)-handed circular polarization mode, which, to our knowledge, are the highest reported values in the VUV range. Despite some uneven photon energy efficiency, the OPHELIE crossed undulator behaves as expected in terms of polarization, permitting full control of the emitted polarization by manipulation of the vertical-to-horizontal magnetic field ratio (rho(und)) and the relative longitudinal phase (phi(und)).     

X-ray techniques using synchrotron radiation in materials analysis

The extraordinary properties of SR have opened up new horizons for all techniques which use vacuum ultraviolet light and X-rays. In this article, some applications of SR in materials science have been discussed. X-ray absorption spectroscopy is a local, atom specific probe of the geometrical and electronic structure of the absorbing species. As an example, the lattice site location and the valence of Co in a doped high-T_c, superconductor YBa₂Cu_2–5Co_0–5O_7–4 has been discussed.     

Residual stresses in particle-reinforced ceramic composites using synchrotron radiation

Residual stresses were determined in particle-reinforced ceramic composites using synchrotron based x-ray diffraction. The baseline Si₃N₄ and the Si₃N₄-TiN composites were processed by turbomilling, pressure casting, and isopressing. They were then continuously sintered to full density, under a pressureless, flowing nitrogen atmosphere. The flexural strength, fracture toughness, and residual stress were measured for as-machined samples and following quenching in water from 1000°C, 1100°C, and 1200°C. The residual stresses for both the baseline Si₃N₄ and the Si₃N₄-TiN composites were determined from the (441) and (531) reflections, by applying the 2-sin² method. The measured residual stresses were compared with the flexural strength and fracture toughness results to determine the effects of residual stress and thermal shocking on the mechanical properties of each material. In both the baseline Si₃N₄ and Si₃N₄-TiN composites, after thermal shocking, the compressive residual stresses were developed in directions both parallel and perpendicular to the sample surface. The residual compressive stresses for the Si₃N₄-TiN composites were much higher than the baseline Si₃N₄. As a result, both fracture toughness and flexural strength of the Si₃N₄-TiN composites were improved. In addition, the addition of the TiN appears to improve both the strength and toughness of the baseline Si₃N₄.     

Studies of photon induced gas desorption using synchrotron radiation

In view of finalizing the design of the vacuum system of the Large Electron and Positron Storage Ring (LEP) we have studied synchrotron radiation induced neutral gas desorption. A 3 m section of an aluminum vacuum chamber has been exposed to the photon beam emerging from the electron storage ring DCI in Orsay, under conditions closely simulating the environment in a particle acceletor. In order of importance the gases desorbed were H₂, CO₂, CO and CH₄ with H₂O practically absent. Under the experimental conditions of an unbaked chamber and 11 mrad glancing incidence of the photons, the initial molecular desorption yields for these gases were typically 0.5, 8 × 10^?2, 2 × 10^?2 and 8 × 10^?3 molecules per photon respectively. These values could be reduced by about 1 to 2 orders of magnitude during continued photon exposure and most cases without evidence that this ‘beam cleaning action’ would be limited. After exposure to air and pumpdown of the previously cleaned chamber, we observe a significant memory effect. The dependence of the photon desorption on the angle of incidence has been studied down to a glancing angle of 11 mrad showing a definite deviation from the previously assumed 1/sin ø scaling. The implications of the results in terms of the expected beam-gas lifetime in LEP are discussed.     

Photoionization studies of atoms and molecules using synchrotron radiation

Photoionization studies of free atoms and molecules have undergone considerable development in the past decade, in large part due to the use of synchrotron radiation. The tunability of synchrotron radiation has permitted the study of photoionization processes near valence- and core-level ionization thresholds for atoms and molecules throughout the Periodic Table. A general illustration of these types of study will be presented, with emphasis on a few of the more promising new directions in atomic and molecular physics being pursued with synchrotron radiation.     

Calculations for the availability of photoneutron using synchrotron radiation

The availability of the neutrons due to photonuclear reactions has been discussed by using synchrotron radiation with the beryllium targets. The superconducting wiggler with the magnetic field of approximately 10 T, which is installed into an 8 GeV class storage ring, can emit intense and high-energy photons to produce neutrons. By using MCNPX, the simulations were performed for the conceptual design of the neutron beamline to estimate the available intensity and to investigate the shield conditions. The results were discussed in comparison with other research reactors.     

Extremely narrowed spontaneous emission spectrum induced by elliptically polarized light

Abstract

We demonstrate the control of spontaneous emission from a five-level atom embedded in a modified reservoir under the action of a single control beam with elliptical polarization. For different initial-state preparations, we take into account the influence of the phase difference between the two circularly polarized components of the control beam on the behavior of spontaneous emission. For the ground initial states, the spontaneous emission spectrum usually shows ultranarrow central lines which are greatly enhanced. In contrast, for the excited initial states, these enhanced ultranarrow lines are significantly suppressed due to the destructive quantum interference. Furthermore, our numerical simulations indicate that the multipeak structure appears in the presence of the elliptically polarized control beam and external magnetic field. Such a scheme for controlling spontaneous emission may find applications in high-precision spectroscopy.     

UHV-type synchrotron radiation reflectometer

We designed a reflectometer for grazing-incidence X-ray measurements with a rotational feedthrough consisting of three welded bellows and a circle-type goniometer. This apparatus does not require differential pumping and is suitable for ultra-high-vacuum applications. With this reflectometer, we successfully performed high-precision synchrotron radiation X-ray reflectivity measurements on a thin iron-film under an ultra-high-vacuum condition.     

Three-dimensional microtomography with synchrotron radiation using planar integral projection data

An investigation of the possibility of reconstructing a three-dimensional object on a microscopic scale using the planar-integral technique with a synchrotron radiation source is presented. It is shown that the proposed planar-integral technique offers a realistic approach for 3-D tomography on a microscopic scale aimed towards spatial resolution within the μm range.     

Construction and performance of an elliptically polarized undulator of type Apple-II

Ten years ago, an elliptically polarized undulator (EPU) with a periodic length of 56?mm was constructed at the Taiwan Light Source. It was the longest EPU at that time. An electron beam of energy 1.5?GeV and current 300?mA passes through the undulator gap and radiates variously polarized light in the soft X-ray spectral domain. This EPU was extensively used in a wide range of research fields, including inelastic scattering, spin-polarized photoemission spectroscopy, photoelectron emission microscopy, and soft X-ray scattering. In response to increased demand by users with differing experimental requirements and applications, the construction of an EPU with a period of length 46?mm is under way. This investigation describes many aspects of the magnetic design, the structural engineering, and the control system. As magnetic technology is undergoing dramatic advances, advanced mechanical devices, and mechanisms have been included in the new EPU design; this design and its differences from the earlier design are summarized here.     

Development of magnesium alloys:Advanced characterization using synchrotron radiation techniques

Magnesium alloys are the lightest metal structural materials owing to their excellent physical and chem-ical properties.Microstructural evolution in magnesium alloys under the conditions of casting,thermal-mechanical processing,and in-service environment,play an important role in governing their mechanical properties and reliability/sustainability.A synchrotron light source produces high flux,tunable X-ray en-ergy,high resolution,and high coherence X-ray beams,which can realize in-situ dynamic observation of microstructural evolution in a wide range of alloys during the entire processing chain and in simulated service environments.This article reviews the fundamentals of synchrotron radiation characterization techniques(imaging,diffraction,scattering,and fluorescence holography)and state-of-the-art advanced synchrotron characterization techniques on the microstructure evolution mechanism of magnesium al-loys.Case studies span a broad range of solidification,deformation,precipitation,fracture and damage,corrosion,and energy storage.Research opportunities and challenges of physical metallurgy studies of magnesium alloys are highlighted for future studies.     

Quantum efficiency measurement of CsI photocathodes using synchrotron radiation at BSRF

A quantum efficiency(QE) measurement system has been established for CsI photocathodes in the wavelength range of 120-210 nm by using the synchrotron radiation light source at Beijing Synchrotron Radiation Laboratory (BSRF). An AXUV100G photodiode calibrated by Physikalisch-Technische Bundesanstalt (PTB) was used as the transfer detector standard to ensure the accuracy and reliability of the QE measurement. The dependencies of QE measurement on beam energy, vacuum pressure and bias voltage were studied in detail. The influence of photoionization in gas on the QE measurement was observed and is described. The surface morphological characteristics of both substrate and CsI film were analyzed by atomic force microscopy (AFM). The QE results of differently prepared CsI photocathodes were compared, including: the printed circuit board (PCB) of FR-4 (Woven glass and epoxy)+Cu, FR-4+Cu/Ni/Au, and stainless steel substrates; a series of thickness from 60 to 600 nm; and the resistive and electron beam evaporation techniques.     

Spatial coherence of synchrotron radiation

The spatial coherence properties of a monochromatic component of synchrotron radiation from an insertion device in the Fraunhofer limit are analyzed in the general case when the coherence distance is comparable with the beam width, expressing them by simple products and convolutions of Fourier transforms and autocorrelations on the single-electron field amplitude and the electron-beam position and angular distributions. In particular, the Gaussian approximation is discussed, in which case the far-field amplitude satisfies the Schell condition (its statistical properties can be described by a coherence factor depending only on the difference of the reciprocal space coordinates), and this discussion leads to simple estimates of the coherence widths. The coherence widths deviate from the Van Cittert-Zernike values when one or more of the phase space widths of the electron beam are close to (or smaller than) the diffraction limit.     

Probing the dynamics of nanoparticle growth in a flame using synchrotron radiation

Flame synthesis is one of the most versatile and promising technologies for large-scale production of nanoscale materials. Pyrolysis has recently been shown to be a useful route for the production of single-walled nanotubes, quantum dots and a wide variety of nanostructured ceramic oxides for catalysis and electrochemical applications. An understanding of the mechanisms of nanostructural growth in flames has been hampered by a lack of direct observations of particle growth, owing to high temperatures (2,000 K), rapid kinetics (submillisecond scale), dilute growth conditions (10(-6) volume fraction) and optical emission of synthetic flames. Here we report the first successful in situ study of nanoparticle growth in a flame using synchrotron X-ray scattering. The results indicate that simple growth models, first derived for colloidal synthesis, can be used to facilitate our understanding of flame synthesis. Further, the results indicate the feasibility of studies of nanometre-scale aerosols of toxicological and environmental concern.