Micron-sized atom traps made from magneto-optical thin films

We have produced magnetic patterns suitable for trapping and manipulating neutral atoms on a 1-m length scale. The required patterns are made in Co/Pt thin films on a silicon substrate, using the heat from a focused laser beam to induce controlled domain reversal. In this way we draw lines and paint shaped areas of reversed magnetisation with sub-micron resolution. These structures produce magnetic microtraps above the surface that are suitable for holding rubidium atoms with trap frequencies as high as 1 MHz. PACS 39.25.+k; 03.75.Be; 75.50.Ss; 75.70.-i     

Plasma Photocathodes

Plasma wakefield accelerators offer accelerating and focusing electric fields three to four orders of magnitude larger than state-of-the-art radiofrequency cavity-based accelerators. Plasma photocathodes can release ultracold electron populations within such plasma waves and thus open a path toward tunable production of well-defined, compact electron beams with normalized emittance and brightness many orders of magnitude better than state-of-the-art. Such beams will have far-reaching impact for applications such as light sources, but also open up new vistas on high energy and high field physics. This paper reviews the innovation of plasma photocathodes, and reports on the experimental progress, challenges, and future prospects of the approach. Details of the proof-of-concept demonstration of a plasma photocathode in 90° geometry at SLAC FACET within the E-210: Trojan Horse program are described. Using this experience, alongside theoretical and simulation-supported advances, an outlook is given on future realizations of plasma photocathodes such as the upcoming E-310: Trojan Horse-II program at FACET-II with prospects toward excellent witness beam parameter quality, tunability, and stability. Future installations of plasma photocathodes also at compact, hybrid plasma wakefield accelerators, will then boost capacities and open up novel capabilities for experiments at the forefront of interaction of high brightness electron and photon beams.     

THE PHOTOPHYSICAL CONSTANTS OF SEVERAL FLUORESCENT DYES PERTAINING TO ULTRASENSITIVE FLUORESCENCE SPECTROSCOPY

Abstract— The successful implementation of ultrasensitive fluorescence spectroscopy of biological and chemical species depends upon certain photophysical parameters associated with the fluorescent dye used in the investigation. These parameters include the fluorescence quantum efficiency, photodestruction quantum efficiency, absorption cross section and fluorescence lifetime. These photophysical constants were measured for several fluorescent dyes that are used for the tagging of biological species. Three different solvents, ethanol, water and a cationic surfactant used above its critical micelle concentration, were studied. The effective photon yield (ratio of the fluorescence quantum yield to the photodestruction quantum efficiency) for the dyes is nearly 100 times greater in ethanol than it is in water because of the superior photostabilities of these dyes in ethanol solvents. The implications of these parameters for the design of an ultrasensitive fluorescence experiment are discussed.     

Experimental investigation of steel spheres as a passive enhancement technique for flash boiling of HCFC-22

An experimental investigation was conducted to study the influence of a layer of 3.6-mm-diameter steel spheres on the mass flow during flash boiling in a glass pressure vessel. It was observed that the steel spheres added numerous heterogeneous nucleation sites within the liquid and promoted abundant vapor bubble growth during depressurization. The steel spheres were in contact with each other and with the interior of the glass vessel. The data from these experiments were compared with baseline experimental results primarily with regard to the mass flow. Each test was run for 60 s, using controlled variables of orifice diameters (1.59 and 5.56 mm), initial refrigerant amounts (0.23, 0.45, and 0.68 kg), initial pressures (575 and 840 kPa), and vessel geometries (665 and 1110 ml). Pressures, temperatures, and mass flow rates, along with calculated saturation temperatures, amount of superheat, mass flux, and total mass flashed, were used to compare the baseline experiments with the enhanced boiling method. Results showed an increase in the total mass flashed at each test condition, ranging from an average of 22% to 81% with respect to baseline experiments.     

Spatially Controlled Occlusion of Polymer‐Stabilized Gold Nanoparticles within ZnO

In principle, incorporating nanoparticles into growing crystals offers an attractive and highly convenient route for the production of a wide range of novel nanocomposites. Herein we describe an efficient aqueous route that enables the spatially controlled occlusion of gold nanoparticles (AuNPs) within ZnO crystals at up to 20 % by mass. Depending on the precise synthesis protocol, these AuNPs can be (i) solely located within a central region, (ii) uniformly distributed throughout the ZnO host crystal or (iii) confined to a surface layer. Remarkably, such efficient occlusion is mediated by a non‐ionic water‐soluble polymer, poly(glycerol monomethacrylate)₇₀ (G₇₀), which is chemically grafted to the AuNPs; pendent cis‐diol side groups on this steric stabilizer bind Zn²⁺ cations, which promotes nanoparticle interaction with the growing ZnO crystals. Finally, uniform occlusion of G₇₀‐AuNPs within this inorganic host leads to faster UV‐induced photodegradation of a model dye.     

Synthetic dynamic test of base line popping noise in recording heads

This paper examines the Base Line Popping Noise (BLPN) test that is used for inspection of instability and electrostatic discharge (ESD) related parameters. The conventional BLPN measurement is performed only by a dynamic tester and shown numerically. A novel BLPN method which is characterized by a synthetic dynamic test under static control is proposed. The results, compared with a conventional one, show that BLPN is thoroughly sensitive to examined parameters such as bias current, operating frequency and ESD zapping voltage. Some hysteresis loop clearly shows the occurrence of BLPN due to Barkhausen jumps which are undetectable by using a typical dynamic tester.     

New measurement of the cosmic-ray positron fraction from 5 to 15 GeV

We present a new measurement of the cosmic-ray positron fraction at energies between 5 and 15 GeV with the balloon-borne HEAT-pbar instrument in the spring of 2000. The data presented here are compatible with our previous measurements, obtained with a different instrument. The combined data from the three HEAT flights indicate a small positron flux of nonstandard origin above 5 GeV. We compare the new measurement with earlier data obtained with the HEAT-e(+/-) instrument, during the opposite epoch of the solar cycle, and conclude that our measurements do not support predictions of charge sign dependent solar modulation of the positron abundance at 5 GeV.     

Implementation of a beam deflection system for studies of liquid interfaces on beamline I07 at Diamond

X‐ray optics, based on a double‐crystal deflection scheme, that enable reflectivity measurements from liquid surfaces/interfaces have been designed, built and commissioned on beamline I07 at Diamond Light Source. This system is able to deflect the beam onto a fixed sample position located at the centre of a five‐circle diffractometer. Thus the incident angle can be easily varied without moving the sample, and the reflected beam is tracked either by a moving Pilatus 100K detector mounted on the diffractometer arm or by a stationary Pilatus 2M detector positioned appropriately for small‐angle scattering. Thus the system can easily combine measurements of the reflectivity from liquid interfaces (Q_z > 1 Å^?1) with off‐specular data collection, both in the form of grazing‐incidence small‐angle X‐ray scattering (GISAXS) or wider‐angle grazing‐incidence X‐ray diffraction (GIXD). The device allows operation over the energy range 10–28 keV.