Download or read book Improved Superlattices for Spin Polarized Electron Sources written by V. M. Ustinov and published by . This book was released on 2006 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: Photoemission of polarized electrons from heterostructures based on InAlGaAs/GaAs superlattices with minimum conduction-band offsets is investigated. The comparison of the excitation energy dependence of the photoemission polarization degree with the calculated spectra makes it possible to determine the polarization losses at different stages of the photoemission. A maximum polarization of P = 91% and a quantum efficiency of QE = 0.5% are close to the best results obtained for photocathodes that are based on strained semiconductor superlattices.

Download or read book Advanced Strained Superlattice Photocathodes for Polarized Electron Sources written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Polarized electrons have been essential for high-energy parity-violating experiments and measurements of the nucleon spin structure. The availability of a polarized electron beam was crucial to the success of the Stanford Linear Collider (SLC) in achieving a precise measurement of the electroweak mixing angle, and polarized electron beams will be required for all future linear colliders. Polarized electrons are readily produced by GaAs photocathode sources. When a circularly polarized laser beam tuned to the bandgap minimum is directed to the negative-electron-affinity (NEA) surface of a GaAs crystal, longitudinally polarized electrons are emitted into vacuum. The electron polarization is easily reversed by reversing the laser polarization. The important properties of these photocathodes for accelerator applications are: degree of polarization of the extracted beam; ability to extract sufficient charge to meet accelerator pulse-structure requirements; efficiency and stability of operation; and absence of any asymmetries in the beam properties (charge, position, energy, etc.) upon polarization reversal. The performance of GaAs photocathodes has improved significantly since they were first introduced in 1978 [1]. The theoretical maximum polarization of 50% for natural GaAs was first exceeded in 1991 using the lattice mismatch of a thin InGaAs layer epitaxially grown over a GaAs substrate to generate a strain in the former that broke the natural degeneracy between the heavy- and light-hole valence bands [2]. Polarizations as high as 78% were produced for the SLC from photocathodes based on a thin GaAs epilayer grown on GaAsP [3,4]. After 10 years of experience with many cathode samples at several laboratories [5], the maximum polarization using the GaAs/GaAsP single strained-layer cathode remained limited to 80%, while the quantum efficiency (QE) for a 100-nm epilayer is only 0.3% or less. Two factors were known to limit the polarization of these cathodes: (1) the limited band splitting; and (2) a relaxation of the strain in the epilayer since the 10-nm critical thickness for maintaining perfect strain is exceeded for a 1 % lattice-mismatch [6]. Strained superlattice structures, consisting of very thin quantum well layers alternating with lattice-mismatched barrier layers are excellent candidates for higher polarization. Due to the difference in the effective mass of the heavy- and light-holes, a superlattice exhibits a natural splitting of the valence band, which adds to the strain-induced splitting. In addition, each of the SL layers is thinner than the critical thickness. Polarized photoemission from strained InGaAs/GaAs [7], InGaAdAlGaAs [8], and GaAs/GaAsP [9,10] superlattice structures have been reported in the literature. For this Phase II program, SVT Associates worked with the Stanford Linear Accelerator Center (SLAC) and University of Wisconsin at Madison to create photocathodes with improved polarization by employing GaAs/GaAsP superlattices. These superlattices consist of alternating thin layers of GaAs and GaAsP. The thicknesses and alloy compositions are designed to create a strained GaAs photoemission layer. Under strain, the heavy-hole and light-hole valence bands in GaAs split, removing degeneracy and allowing high polarization, theoretically 100%. This final report discusses the efforts and results achieved, comparing the device performance of newly created superlattice photocathodes grown by molecular beam epitaxy (MBE) with the devices created by other fabrication technologies, and efforts to optimize and improve the device operation.

Download or read book Resonance Enhancement of Spin Polarized Electron Emission from Strain Compensated AlInGaAs GaAsP Superlattices written by J. S. Roberts and published by . This book was released on 2006 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: Resonance enhancement of the quantum efficiency of new polarized electron photocathodes based on a short-period strain-compensated AlInGaAs/GaAsP superlattice structure is reported. The superlattice is a part of an integrated Fabry-Perot optical cavity. We demonstrate that the Fabry-Perot resonator enhances the quantum efficiency by up to a factor 10 in the wavelength region of the main polarization maximum. The high structural quality implied by these results points to the very promising application of these photocathodes for spin-polarized electron sources.

Download or read book Highly Polarized Electron Emission from Strain Compensated Superlattices and Superlattices with High Valence Band Splitting written by and published by . This book was released on 2004 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results of experimental and theoretical studies of polarized electron emission from new short-period strain-compensated InAlGaAs-GaAsP superlattices and InAlGaAs-AlGaAs superlattices with a high-valence-band splitting are presented. The superlattice structures investigated are found to be very promising for spin-polarized electron sources.

Download or read book Proceedings of the 17th International Spin Physics Symposium written by Kenichi Imai and published by American Inst. of Physics. This book was released on 2007-07-02 with total page 1196 pages. Available in PDF, EPUB and Kindle. Book excerpt: Getting down to the bottom line is what this proceedings digest is all about, as any physicist will tell you: spin is the fundamental concept in physics. The applications are pretty universal due to the fact that, using spin-related phenomena, physicists are trying to reveal the fundamental principles of nature – and things don’t come much more bottom-line than that. This volume is the proceedings of the 17th International Spin Physics Symposium which is a forum to discuss spin physics and related topics.

Download or read book Polarized Sources And Targets Proceedings Of The Eleventh International Workshop written by Akihiro Yoshimi and published by World Scientific. This book was released on 2007-04-26 with total page 269 pages. Available in PDF, EPUB and Kindle. Book excerpt: Polarized beams and targets have been irreplaceable tools in nuclear and particle physics experiments for a long time and have provided us rich information on the role played by spin-degrees of freedom in the sub-nuclear world. In addition, techniques to obtain large nuclear polarization have recently been applied to new fields such as materials and medical sciences.The scope of these proceedings covers recent progress of state-of-the-art techniques in spin polarization, the cryogenic method, the atomic beam method, the optical pumping method and the nuclear reaction method.

Download or read book Strain Compensated A1InGaAs GaAsP Superlattices for Highly Polarized Electron Emission written by J. Clendenin and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Spin-polarized electron emission from the first superlattice photocathodes developed with strain compensation is investigated. An opposite strain in the quantum well and barrier layers is accomplished using an InAlGaAs/GaAsP superlattice structure. The measured values of maximum polarization and quantum yield for the structure with a 0.18 {micro}m-thick working layer are close to the best results reported for any strained superlattice photocathode structure, demonstrating the high potential of strain compensation for future photocathode applications. An analysis of the photoemission spectra is used to estimate the parameters responsible for the polarization losses.

Download or read book Polarized Sources And Targets Proceedings Of The Ninth International Workshop written by Vladimir (Laddie) Derenchuk and published by World Scientific. This book was released on 2002-05-16 with total page 397 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is an up-to-date survey of the science and technology of creating polarized beams and polarized targets. The papers in this collection describe state-of-the-art sources of polarized electrons, ions, atoms, neutrons, and radioactive isotopes, discuss new polarized solid and gas target techniques, present recent advances in polarimetry, and review the use of polarized gas in medical imaging.

Download or read book Photoelectron Spectroscopy written by Shigemasa Suga and published by Springer Nature. This book was released on 2021-08-01 with total page 511 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents photoelectron spectroscopy as a valuable method for studying the electronic structures of various solid materials in the bulk state, on surfaces, and at buried interfaces. This second edition introduces the advanced technique of high-resolution and high-efficiency spin- and momentum-resolved photoelectron spectroscopy using a novel momentum microscope, enabling high-precision measurements down to a length scale of some tens of nanometers. The book also deals with fundamental concepts and approaches to applying this and other complementary techniques, such as inverse photoemission, photoelectron diffraction, scanning tunneling spectroscopy, as well as photon spectroscopy based on (soft) x-ray absorption and resonance inelastic (soft) x-ray scattering. This book is the ideal tool to expand readers’ understanding of this marvelously versatile experimental method, as well as the electronic structures of metals and insulators.

Download or read book Proceedings of the Ninth International Workshop Polarized Sources and Targets written by Vladimir P. Derenchuk and published by World Scientific. This book was released on 2002 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is an up-to-date survey of the science and technology of creating polarized beams and polarized targets. The papers in this collection describe state-of-the-art sources of polarized electrons, ions, atoms, neutrons, and radioactive isotopes, discuss new polarized solid and gas target techniques, present recent advances in polarimetry, and review the use of polarized gas in medical imaging.

Download or read book InP and Related Compounds written by M O Manasreh and published by CRC Press. This book was released on 2000-08-08 with total page 870 pages. Available in PDF, EPUB and Kindle. Book excerpt: InP is a key semiconductor for the production of optoelectronic and photonic devices. Its related compounds, such as InGaAsP alloy, have been realized as very important materials for communication in the 1.3 and 1.55 micron spectral regions. Furthermore, the applications on InP and related compounds have extended to other areas that include laser diodes, light emitting diodes, photodetectors, waveguides, photocathodes, solar cells, and many other applications. The topics presented in this book have been chosen to achieve a balance between the properties of bulk materials, doping, characterization, applications, and devices. This unique volume, featuring chapters written by experts in the field, provides a good starting point for those who are new to the subject and contains detailed results and in depth discussions for those who are experts in the field.

Download or read book Development of Polarized Electron Source for Future Linear Colliders Using AIGaAs GaAs Superlattice written by T. Omori and published by . This book was released on 1992 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Atomic Molecular and Optical Physics Charged Particles written by and published by Academic Press. This book was released on 1995-11-29 with total page 485 pages. Available in PDF, EPUB and Kindle. Book excerpt: With this volume, Methods of Experimental Physics becomes Experimental Methods in the Physical Sciences, a name change which reflects the evolution of todays science. This volume is the first of three which will provide a comprehensive treatment of the key experimental methods of atomic, molecular, and optical physics; the three volumes as a set will form an excellent experimental handbook for the field. The wide availability of tunable lasers in the pastseveral years has revolutionized the field and lead to the introduction of many new experimental methods that are covered in these volumes. Traditional methods are also included to ensure that the volumes will be a complete reference source for the field.

Download or read book Modern Developments in Vacuum Electron Sources written by Georg Gaertner and published by Springer Nature. This book was released on 2020-10-09 with total page 609 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book gives an overview of modern cathodes and electron emitters for vacuum tubes and vacuum electron devices in general. It covers the latest developments in field emission theory as well as new methods towards improving thermionic and cold cathodes. It addresses thermionic cathodes, such as oxide cathodes, impregnated and scandate cathodes, as well as photocathodes and field emitters – the latter comprising carbon nanotubes, graphene and Spindt-type emitter arrays. Despite the rise and fall of the once dominant types of vacuum tubes, such as radio valves and cathode ray tubes, cathodes are continually being improved upon as new applications with increased demands arise, for example in electron beam lithography, high-power and high-frequency microwave tubes, terahertz imaging and electron sources for accelerators. Written by 17 experts in the field, the book presents the latest developments in cathodes needed for these applications, discussing the state of the art and addressing future trends.

Download or read book Polarized Sources Targets and Polarimetry written by Giuseppe Ciullo and published by World Scientific. This book was released on 2011 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book collects the most recent experimental results, new ideas and prototypes in the field of nuclear gaseous and solid polarized targets and polarimetry. It contains the contribution of the biennial meeting on the topics of Polarized Sources, Targets and Polarimetry. Therefore includes the most recent developments and performances in the field and new proposals. The contributing authors are the experts of the field. The topics covered include: Polarized Electron Sources, Polarized Proton and Deuterium Sources, Polarized Internal Targets, Polarized 3He Ion Sources and Targets, Polarimetry (e, p, d) at Low and High Energy, Polarized antiprotons, Polarized Solid Targets.

Download or read book Energy Research Abstracts written by and published by . This book was released on 1994-11 with total page 486 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book International Workshop on Nondestructive Testing and Computer Simulations in Science and Engineering written by and published by . This book was released on 2001 with total page 546 pages. Available in PDF, EPUB and Kindle. Book excerpt: